MAKING SCHOOLS SAFE AGAINST WINDS     6


6.1 INTRODUCTION

A well-designed, constructed, and maintained school may be damaged by a 
wind event that is much stronger than what the building was designed for; however, 
except for tornado damage, this scenario is a very rare occurrence. Rather, most 
damage occurs because various building elements have limited wind resistance due to 
inadequate design, application, or material deterioration. Wind with sufficient speed 
to cause damage to weak schools can occur anywhere in the United States and its 
possessions.1 Although the magnitude and frequency of strong windstorms varies by 
locale, all schools should and can be designed, constructed, and maintained to avoid 
wind damage (other than that associated with tornadoes). In tornado-prone regions, 
consideration should be given to designing and constructing portions of schools to 
provide occupant protection.2
This chapter discusses structural and nonstructural building components and 
illustrates a variety of wind-induced damages. Because of the frequency and 
significant consequences of nonstructural component failure, emphasis is given to 
these elements. 
Numerous examples of best practices pertaining to new and existing schools are 
presented for consideration. Incorporation of those practices that are applicable to a 
specific project will result in greater wind-resistance reliability and will, therefore, 
provide enhanced protection for occupants and decreased expenditures for repair of 
wind-damaged facilities. 



6.2 THE NATURE AND PROBABILITY OF HIGH WINDS

A variety of windstorm types occur in different areas of the U.S. The characteristics of 
the type of storms that can impact the site should be considered by the design team. 
The primary storm types are:

¥ Straight-line wind. This type of wind event is the most common. The wind is 
considered, in general, to blow in a straight line. Straight-line wind speeds range 
from very low to very high. High winds associated with intense low pressure can 
last for upward of a day at a given location. Straight-line winds occur throughout 
the U.S. and its possessions (see Figure 6-1).

¥ Down-slope wind. Wind flowing down the slope of mountains is referred to as down-
slope wind. Down-slope winds with very high wind speeds frequently occur in 
Alaska and Colorado. In the continental U.S., mountainous areas are referred to as 
"special wind regions" (see Figure 6-1). Neither ASCE 7 or model building codes 
provide guidance on wind speeds in special wind regions. If the local building 
department has not established the basic speed, use of regional climatic data and 
consultation with a wind engineer or meteorologist is advised. 
¥ Thunderstorm. This type of storm can rapidly form and produce high wind speeds. 
Approximately 10,000 severe thunderstorms occur in the U.S. each year, typically in 
the spring and summer. They are most common in the Southeast and Midwest. 
Besides producing high winds, they often create heavy rain. Hail and tornadoes 
are also sometimes produced. Thunderstorms commonly move through an area 
quite rapidly, often causing high winds for only a few minutes at a given location. 
However, thunderstorms can also stall and become virtually stationary.

¥ Downburst. Also known as microburst, it is a powerful downdraft associated with a 
thunderstorm. When the downdraft reaches the ground, it spreads out 
horizontally and may form one or more horizontal vortex rings around the 
downdraft. The outflow is typically 6,000 to 12,000 feet across and the vortex ring 
may rise 2,000 feet above the ground. The life-cycle of a downburst is usually 
between 15 to 20 minutes. Observations suggest that approximately 5 percent of all 
thunderstorms produce a downburst, which can result in significant damage in a 
localized area.

¥ Northeaster (nor'easter). This type of storm is cold and violent and occurs along the 
northeastern coast of the U.S. These storms blow in from the Northeast and may 
last for several days.

¥ Hurricane. This is a system of spiraling winds converging with increasing speed 
toward the storm's center (the eye of the hurricane). Hurricanes form over warm 
oceans. The diameter of the storm varies between 50 and 600 miles. A hurricane's 
forward movement (translational speed) can vary between approximately 10 to 25 
miles per hour (mph). Besides being capable of delivering extremely strong winds 
for several hours, many hurricanes also bring very heavy rainfall. Hurricanes also 
occasionally spawn tornadoes. The Saffir-Simpson Hurricane Scale rates the 
intensity of hurricanes. The five-step scale ranges from Category I (the weakest) to 
Category V (the strongest). Hurricane-prone regions are defined in Section 
6.2.1.Of all the storm types, hurricanes have the greatest potential for devastating a 
very large geographical area and, hence, affect great numbers of people. The terms 
"hurricanes, tropical cyclones, and typhoons" are synonymous for the same type of 
storm. See Figure 6-1 for hurricane-prone regions.

¥ Tornado. This is a violently rotating column of air extending from the base of a 
thunderstorm to the ground. The Fujita scale categorizes tornado severity based 
on observed damage. The six-step scale ranges from F0 (light damage) to F5 
(incredible damage). Weak tornadoes (F0 and F1) are most common, but strong 
tornadoes (F2 and F3) frequently occur. Violent tornadoes (F4 and F5) are rare. 
Tornado path widths are typically less than 1,000 feet; however, widths of 
approximately 1 mile have been reported. Wind speed rapidly decreases with 
increased distance from the center of a tornado. A school on the periphery of a 
strong or violent tornado could be subjected to moderate to high wind speeds, 
depending upon the distance from the core of the tornado. However, even though 
the wind speed might not be great, a school on the periphery could still be 
impacted by many large pieces of wind-borne debris. Tornadoes are responsible 
for the greatest number of wind-related deaths each year in the U.S. Figure 6-2 
shows frequency of occurrence for 1950 to 1998 and Figure 6-3 shows the design 
wind speeds used for the design of community tornado shelters.


6.2.1 Wind/Building Interactions 

When wind interacts with a building, both positive and negative (i.e., suction) 
pressures occur simultaneously (see Figure 6-4). (Note: negative pressures are less 
than ambient pressure, and positive pressures are greater than ambient pressure.) 
The school must have sufficient strength to resist the applied loads in order to 
prevent wind-induced building failure. The magnitude of the pressures is a function 
of the following primary factors:

¥ Exposure. The characteristics of the ground roughness and surface irregularities in 
the vicinity of a building influence the wind loading. ASCE 7 defines three 
exposure categories, Exposures B, C, and D.3 Exposure B is the roughest terrain 
and Exposure D is the smoothest. Exposure B includes urban, suburban, and 
wooded areas. Exposure C includes flat open terrain with scattered obstructions 
and areas adjacent to water surfaces in hurricane-prone regions (which are 
defined below under "basic wind speed"). Exposure D includes areas adjacent to 
water surfaces outside hurricane-prone regions, mud flats, salt flats, and unbroken 
ice. Because of the wave conditions generated by hurricanes, areas adjacent to 
water surfaces in hurricane-prone regions are considered to be Exposure C rather 
than the smoother Exposure D.The smoother the terrain, the greater the wind 
load; therefore, schools (with the same basic wind speed) located in Exposure D 
would receive higher wind loads than those located in Exposure C. 

¥ Basic wind speed. ASCE 7 defines the basic wind speed as the wind speed with a 50-
year mean recurrence interval (2 percent annual probability), measured at 33 feet 
above grade in Exposure C (flat open terrain). If the building is located in 
Exposure B or D, rather than C, an adjustment for the actual exposure is made in 
the ASCE 7 calculation procedure.Since the 1995 edition of ASCE 7, the basic wind 
speed has been a peak gust speed. Prior to that time, the basic wind speed was a 
fastest-mile speed (i.e., the speed averaged over the time required for a mile-long 
column of air to pass a fixed point). Because the measuring time for peak gust 
versus fastest-mile is different, peak gust speeds are typically about 20 miles per 
hour (mph) faster than fastest-mile speeds (e.g., a 90-mph peak basic wind speed is 
equivalent to a 70-mph fastest-mile wind speed). Most of the U.S. has a basic wind 
speed (peak gust) of 90 mph, but much higher speeds occur in Alaska and in 
hurricane-prone regions. The highest speed, 170 mph, occurs in Guam. 
Hurricane-prone regions are along the Atlantic and Gulf of Mexico coasts (where 
the basic wind speed is greater than 90 mph), Hawaii, and the U.S. possessions in 
the Caribbean and South Pacific (see Figure 6-1).In determining wind pressures, 
the basic wind speed is squared; therefore, as the velocity is increased, the 
pressures are exponentially increased. For example, the uplift load on a 30-foot 
high roof covering at a corner area of a school in Exposure B is 37.72 pounds per 
square foot (psf) with a basic wind speed of 85 mph (per ASCE 7-02). If the speed is 
doubled to 170 mph, the roof corner load increases by a factor of four to 151 psf.

¥ Topography. Abrupt changes in topography, such as isolated hills, ridges, and 
escarpments, cause wind speed-up; therefore, a school located near a ridge would 
receive higher wind loads than a school located on relatively flat land. ASCE 7 
provides a procedure to account for topographic influences.

¥ Building height. Wind speed increases with height above the ground. Therefore, the 
taller the school, the greater the speed and, hence, the greater the wind loads. 
ASCE 7 provides a procedure to account for building height.

¥ Internal pressure (i.e., building pressurization/depressurization). Wind striking a 
building can cause either an increase in the pressure within the building (i.e., 
positive pressure), or it can cause a decrease in the pressure (i.e., negative 
pressure). Internal pressure changes occur because of the porosity of the building 
envelope. Porosity is caused by openings around doors and window frames, and by 
air infiltration through walls that are not absolutely airtight. A door or window left 
in the open position also contributes to porosity. 

Wind striking an exterior wall exerts a positive pressure on the wall, which forces 
air through openings and into the interior of the building (this is analogous to 
blowing up a balloon). At the same time the windward wall is receiving positive 
pressure, the side and rear walls are receiving negative (suction) pressure; 
therefore, air within the building is being pulled out at openings in these other 
walls. As a result, if the porosity of the windward wall is greater than the combined 
porosity of the side and rear walls, the interior of the building is pressurized. But if 
the porosity of the windward wall is less than the combined porosity of the side 
and rear walls, the interior of the building is depressurized (this is analogous to 
letting air out of a balloon).


When a building is pressurized, the internal pressure pushes up on the roof. This 
push from below the roof is combined with the suction above the roof, resulting 
in an increased wind load on the roof. The internal pressure also pushes on the 
side and rear walls. This outward push is combined with the suction on the 
exterior side of these walls. Therefore, a pressurized building increases the wind 
load on the side and rear walls (see Figure 6-5) as well as on the roof.
 When a building is depressurized, the internal pressure pulls the roof down, which 
reduces the amount of uplift exerted on the roof. The decreased internal pressure 
also pulls inward on the windward wall, which increases the wind load on that wall 
(see Figure 6-6).

 When a school becomes fully pressurized (e.g., due to window breakage), the loads 
applied to the exterior walls and roof are significantly increased. The build-up of 
high internal pressure can also blow down interior partitions and blow ceiling 
boards out of their support grid. The breaching of a small window is typically 
sufficient to cause full pressurization of the school's interior.
 ASCE 7 provides a design procedure to assess the influence of internal pressure on 
the wall and roof loads, and it provides positive and negative internal pressure 
coefficients for use in load calculations. Buildings that can be fully pressurized are 
referred to as partially enclosed buildings. Buildings that have limited internal 
pressurization capability are referred to as enclosed buildings. 

¥ Aerodynamic pressure. Because of building aerodynamics (i.e., the interaction 
between the wind and the building), the highest uplift loads occur at roof corners.  
The roof perimeter has a somewhat lower load, followed by the field of the roof. 
Exterior walls typically have lower loads than the field of the roof. The ends of 
walls have higher suction loads than the portion of wall between the ends. 
However, when the wall is loaded with positive pressure, the entire wall is 
uniformly loaded. Figure 6-7 illustrates these aerodynamic influences. The 
negative values shown in Figure 6-7 indicate suction pressure acting upward from 
the roof surface and outward from the wall surface. Positive values indicate positive 
pressure acting inward on the wall surface.

 Aerodynamic influences are accounted for by use of external pressure coefficients, 
which are used in load calculations. The magnitude of the coefficient is a 
function of the location on the building (e.g., roof corner or field of roof) and 
building shape as discussed below. Positive coefficients represent a positive 
pressure, and negative coefficients represent negative (suction) pressure. External 
pressure coefficients are found in ASCE 7.

 Building shape affects the magnitude of pressure coefficients and, therefore, the 
loads applied to the various building surfaces. For example, the uplift loads on a 
low-slope roof are larger than the loads on a gable or hip roof. The steeper the 
slope, the lower the uplift load. Pressure coefficients for monoslope (shed) roofs, 
sawtooth roofs, and domes are all different from those for low-slope and gable/hip 
roofs.
 Building irregularities such as bay window projections, a stair tower projecting out 
from the main wall, dormers, chimneys, etc., can cause localized turbulence. 
Turbulence causes wind speed-up, which increases the wind loads in the vicinity of 
the building irregularity as shown in Figures 6-8 and 6-9.

As shown in Figure 6-9, the built-up roof's base flashing was pulled out from 
underneath the coping and caused a large area of the membrane to lift and peel. 
Some of the wall covering on the stair tower was also blown away. Had the stair tower 
not existed, the built-up roof would not have been damaged.
Loads exerted on the building envelope are transferred to the structural system, 
where they are transferred through the foundation and into the ground.
Information pertaining to load calculations is presented in Section 6.8.2.
For further general information on the nature of wind and wind-building 
interactions, see Buildings at Risk: Wind Design Basics for Practicing Architects, American 
Institute of Architects, 1997.

To avoid damage in the vicinity of building irregularities, attention needs to be given 
to attachment of building elements located in turbulent flow areas.



6.2.2 Probability of Occurrence

Most buildings are designed for a 50-year mean recurrence interval wind event (2 
percent annual probability). A 50-year storm would be expected to happen about once 
every 50 years; however, a 50-year storm can occur more or less frequently. A 50-year 
storm may not occur within any 50-year interval, but two 50-year storms could occur 
within 1 year.
ASCE 7 requires schools with a capacity greater than 250 occupants and schools used 
for hurricane or other emergency shelters to be designed for a 100-year mean 
recurrence interval wind event (1 percent annual probability); therefore, these 
schools are designed to resist stronger, rarer storms than most buildings. The 
importance factor is used to adjust the mean recurrence interval. For a 50-year 
interval, the importance factor is 1.00. For a 100-year interval, the importance factor is 
1.15. 

When designing a school, architects and engineers should consider the following:

¥ Routine winds. In many locations, winds with low to moderate speeds occur daily. 
Damage is not expected to occur during these events.
¥ Stronger winds. At a given site, stronger winds (e.g., winds with a basic wind speed in 
the range of 70 to 80 mph peak gust) may occur from several times a year to only 
once a year or less frequently. 70 to 80 mph is the threshold at which damage 
normally begins to occur to building elements that have limited wind resistance 
due to problems associated with
 inadequate design, strength, application, or material deterioration.
¥  Design level winds. Schools that experience design level events and 
events that are somewhat in excess of design level should 
experience little, if any damage; however, design level storms 
frequently cause extensive building envelope damage. Structural 
damage also occurs, but less often. Damage experienced with 
design level events is typically associated with inadequate design, 
application, or material deterioration. The exceptions are wind-
driven water infiltration and wind-borne debris (missiles) 
damage. Water infiltration is discussed in Sections 6.10.4, 6.11.3, 
and 6.13.3. 
¥ Tornadoes. Although more than 1,200 tornadoes typically occur each year in the 
U.S., the probability of a tornado occurring at any given location is quite small. 
The probability of occurrence is a function of location. As shown in Figure 6-2, 
only a few areas of the U.S. frequently experience tornadoes, and tornadoes are 
very rare in the west. The Oklahoma City area is the most active location in the 
U.S., with 106 recorded tornadoes between the years 1890 and 2000. 

 Except for window breakage, well designed, constructed, and maintained schools 
should experience little if any damage from weak tornadoes. However, because 
many schools have wind-resistance deficiencies, weak tornadoes often cause 
building envelope damage. Most schools experience significant damage if they are 
in the path of a strong or violent tornado (see Figure 6-10). In the classroom wing, 
shown in Figure 6-10, all of the exterior windows were broken, and virtually all of 
the cementitious wood-fiber deck panels were blown away. Much of the metal 
decking over the band and chorus area also blew off. The gymnasium collapsed, as 
did a portion of the multi-purpose room. The school was not in session at the time 
the tornado struck.



6.3 VULNERABILITY: WHAT WIND CAN DO TO SCHOOLS
  
When damaged by wind, schools typically experience the following types of building 
component damage in descending order of frequency of occurrence (see Figures 6-11 
through 6-16):
Ramifications of the above types of damages include: 

¥ Property damage. Including repair/replacement of the damaged components (or 
replacement of the entire facility), plus repair/replacement of interior building 
components, mold remediation, furniture, equipment, and books caused by water 
and/or wind entering the school. Even when damage to the building envelope is 
limited, such as blow-off of a portion of the roof covering or broken glazing, 
substantial water damage frequently occurs because heavy rains often accompany 
strong winds (particularly in the case of thunderstorms, hurricanes, and 
tornadoes; see Figure 6-17).  

 Debris such as roof aggregate, gutters, HVAC equipment, and siding blown from 
schools can damage automobiles, residences, and other buildings in the vicinity 
of the school.
 Debris can travel well in excess of 300 feet in wind events. If non-school property is 
damaged by school building debris, the school district will likely be responsible 
for the damage.
 Portable classrooms are often particularly vulnerable to significant damage because 
they are seldom designed to the same wind loads as permanent school buildings. 
Portable
classrooms are frequently blown over during high-wind events 
because the inexpensive techniques that are typically used are 
inadequate to anchor the units to the ground. Wind-borne debris 
from portables or an entire portable classroom may impact the 
permanent school building and cause serious damage.

¥  Injury or death. Although infrequent, school occupants or people 
outside schools have been injured and killed when struck by 
collapsed building components (such as exterior masonry walls 
or the roof structure) or wind-borne building debris. The greatest 
risk of injury or death is during strong hurricanes and 
strong/violent tornadoes. 

¥  Interrupted use. Depending upon the magnitude of wind and 
water damage, it can take days, months, or more than a year to 
repair the damage or replace a facility (see Figure 6-18). In 
addition to the costs associated with repairing/replacing the 
damage, other financial ramifications related to interrupted use 
of the school can include the cost of bussing students to an 
alternative school and/or rental of temporary facilities. These 
additional costs can be quite substantial. 
There are also social and psychological factors, such as difficulties imposed on 
students, parents, faculty and the administration during the time the school is not 
usable.




6.4 SCOPE, EFFECTIVENESS, AND LIMITATIONS OF BUILDING CODES

In the following section, the IBC is discussed. In some jurisdictions, NFPA 5000 or 
one of the earlier model building codes or a specially written state or local building 
code may be used. The specific scope and/or effectiveness and limitations of these 
other building codes will be somewhat different than that of the IBC. It is incumbent 
upon the architect/engineer to be aware of the specific code (including the edition 
of the code and local amendments) that has been adopted by the authority having 
jurisdiction.  

6.4.1 Scope

With respect to wind performance, the scopes of the model building codes have 
greatly expanded since the mid-1980s. Significant improvements include:
¥ Recognition of increased uplift loads at the roof perimeter and corners. Prior to the 
1982 edition of the Standard Building Code and Uniform Building Code and the 
1987 edition of the National Building Code, these model codes did not account for 
the increased uplift at the roof perimeter and corners. Therefore, schools 
designed in accordance with earlier editions of these codes are very susceptible to 
blow-off of the roof deck and/or roof covering.

¥ Adoption of ASCE 7 for wind design loads. Although the three model codes 
permitted use of ASCE 7, the 2000 edition of the IBC was the first model code to 
require ASCE 7 for determining wind design loads. ASCE 7 has been more 
reflective of the current state of the knowledge than the model codes, and use of 
this procedure has typically resulted in higher design loads. 
¥ Roof coverings. Several performance and prescriptive requirements pertaining to 
wind resistance of roof coverings have been incorporated. The majority of these 
additional provisions were added after Hurricanes Hugo (1989) and Andrew 
(1992). Poor performance of roof coverings was widespread in both of those 
storms. Prior to the 1991 edition of the SBC and UBC and the 1990 edition of the 
NBC, these model codes were essentially silent on roof covering wind loads and 
test methods for determining uplift resistance. Code improvements continued to 
be made through the 2003 edition of the IBC.
¥ Glazing protection. The 2000 edition of the IBC was the first model code to address 
wind-borne debris requirements for buildings located in the wind-borne debris 
regions of hurricane-prone regions (via reference to the 1998 edition of ASCE 7). 
(The 1995 edition of ASCE 7 was the first edition to address wind-borne debris 
requirements).
¥ Parapets and rooftop equipment. The 2003 edition of the IBC was the first model 
code to address wind loads on parapets and rooftop equipment (via reference to 
the 2002 edition of ASCE 7, which was the first edition of ASCE 7 to address these 
elements).


6.4.2 Effectiveness

Except for hurricanes and tornadoes, the 2003 edition of the IBC is believed to be a 
relatively effective code, provided that it is properly followed and enforced. This code 
is also believed to be an effective code for hurricanes, except that it does not account 
for water infiltration due to puncture of the roof membrane by missiles, nor does it 
adequately address the vulnerabilities of brittle roof coverings (such as tile) to 
missile-induced damage and subsequent progressive cascading failure.
The 2003 IBC relies on several referenced standards and test methods developed or 
updated in the 1990s. Most of these standards and test methods have not been 
validated by actual building performance during design level wind events. 

Therefore, 
the actual performance of buildings designed and constructed to the minimum 
provisions of the 2003 IBC remains to be determined. Future post-storm building 
performance evaluations may or may not show the need for further enhancements.
The 2003 IBC does not account for tornadoes; therefore, except for weak tornadoes, it 
is ineffective for this type of storm.


6.4.3 Limitations

Limitations to building codes include the following:

¥ Because codes are adopted on the local or state level, the adopting authority has the 
power to not adopt all wind-related provisions of a model code, or to write their 
own code rather than follow a model code. In either case, important provisions of 
the current model code may be stricken, thereby resulting in schools that are 
more susceptible to wind damage when they are designed and constructed in 
accordance with the minimum requirements of the locally adopted code. Also, 
often there is a significant time lag between the time a model code is updated and 
the time it is implemented by the adopting authority. When lag occurs, schools 
designed to the minimum requirements of the outdated code are not taking 
advantage of the current state of the knowledge. Therefore, these schools are 
prone to poorer wind performance compared to schools designed according to 
the current model code.

¥ Adoption of the current model code does not ensure good wind performance.  
Rather, the code is a minimum tool that should be used by knowledgeable design 
professionals in conjunction with their training, skills, and professional 
judgment. To achieve good wind performance, in addition to good design, the 
construction work must be effectively executed and the school must be adequately 
maintained and repaired.

¥ Specific limitations of the 2003 IBC include lack of provisions pertaining to blow-off 
of aggregate from built-up and sprayed polyurethane foam roofs, and limitations 
of some of the test methods used to assess wind and wind-driven rain resistance of 
building envelope components (improved test methods need to be developed 
before this code limitation can be overcome). In addition, the code does not 
address protection of occupants in schools (and other buildings) located in 
tornado-prone regions.

¥ The 2003 IBC does not address the need for continuity, redundancy, or energy-
dissipating capability (ductility) to limit the effects of local collapse and to prevent 
or minimize progressive collapse in the event of the loss of one or two primary 
structural members such as a column. However, even though this issue is not 
addressed in the IBC, Chapter 1 of ASCE 7 does address general structural 
integrity, and the ASCE 7 Chapter 1 Commentary provides some guidance on this 
issue. 



6.5 PRIORITIES, COSTS, AND BENEFITS: NEW SCHOOLS

Prior to evaluating schools for risk from high winds and beginning the risk 
reduction design process, it is first necessary to consider the priorities, costs, and 
benefits of potential risk reduction measures. These factors, as discussed below, 
should be considered within the context of performance-based wind design as 
discussed in Section 2.12.3.


6.5.1 Priorities

As previously discussed in this manual, the first priority is the implementation of 
measures that will reduce risk of casualties to students, faculty, staff, and visitors. The 
second priority is the reduction of damage that leads to downtime and disruption. 
The third priority is the reduction of damage and repair costs. To realize these priori-
ties, as a minimum the school should be designed and constructed in accordance 
with the latest edition of a current model building code such as the IBC (unless the 
local building code has more conservative wind-related provisions, in which case the 
local building code should be used as the basis for design). In addition, the school 
should be adequately maintained and repaired. 

For schools that will be used for emergency response after a storm and/or those 
schools that will be used for hurricane shelters, measures beyond those required by 
the IBC should be given high priority (see Section 6.15).
For schools in coastal Alaska and other areas that experience frequent high-wind 
events (such as parts of Colorado), measures beyond those required by the IBC should 
be given high priority. Several of the recommendations for schools in hurricane-
prone regions (Section 6.15) are also applicable to these schools, with the exception 
of the wind-borne debris recommendations. (Limited amounts of wind-borne debris 
are generated in storms other than hurricanes and tornadoes.)
For schools located in tornado-prone regions, priority should be given to the 
incorporation of specially designed occupant shelters within the school (see Section 
6.16). The decision to incorporate occupant shelters should be based on the 
assessment of risk (see Section 6.7.1). 
 
For schools located in areas where the basic wind speed is greater than 90 mph, 
priority should be given to incorporation of design, construction, and maintenance 
enhancements. The degree of priority given to these enhancements increases as the 
basic wind speed increases (see Sections 6.8.3 to 6.8.5 and 6.9 to 6.14 for enhancement 
examples).


6.5.2 Cost, Budgeting, and Benefits

The cost for complying with the IBC should be considered as the minimum baseline 
cost.  
For schools that will be used for emergency response after a storm and/or those 
schools that will be used for hurricane shelters, the additional cost for implementing 
measures beyond those required by the 2003 edition of the IBC will typically add only 
a small percentage to the total cost of construction. Sections 6.8 and 6.15 discuss ad-
ditional measures that should be considered. 

For all other schools other than those discussed above, the additional cost for 
implementing enhancements will typically add only a very small percentage to the 
total cost of construction. Sections 6.8 to 6.14 discuss additional measures that should 
be considered.

The yearly cost of periodic maintenance and repair will be greater than the 
alternative of not expending any funds for periodic maintenance (i.e., deferred 
maintenance and repair). If, however, the deferred maintenance option is selected, 
eventually maintenance and repairs will be required, and the extent and cost of the 
work will typically be much greater than the costs associated with the periodic option. 
Also, if a windstorm causes damage that would have otherwise been avoided had 
maintenance or repairs been performed, the resulting costs can be significantly 
higher. (Note:  Maintenance and repair costs are reduced when more durable 
materials and systems are used; see Section 6.8.2, under "Step 4: Durability.")
Budgeting. It is important for the school district to give consideration to wind 
enhancement costs early in the development of a new school project. If 
enhancements, particularly those associated with schools used as hurricane shelters, 
emergency response after a storm, and tornado shelters, are not included in the 
initial project budget, often it is very difficult to find funds later during the design of 
the project. If the additional funds are not found, the enhancements may be 
eliminated because of lack of forethought and adequate budgeting. 
Benefits. If strong storms do not occur during the life of a school, there is little 
benefit to spending the money and effort related to wind resistance. However, 
considering the long life of most schools (hence, the greater probability of them 
experiencing a design level event) and considering the importance placed on 
students and the value of the school to the community, clearly it is prudent to invest 
in adequate wind resistance. By doing so, the potential for loss of life and injuries can 
be significantly reduced or virtually eliminated. Investing in wind resistance also 
minimizes future expenditures for repair or replacement of wind-damaged schools 
and avoids costly interrupted building use.
Fortunately, most of the enhancements pertaining to increased wind resistance are 
relatively inexpensive compared to the benefit that they provide. In evaluating what 
enhancements are prudent for a specific school, an enhancement that provides 
greater performance reliability at little cost is an enhancement worthy of 
consideration (see Figure 6-19).
Wind resistance enhancements may also result in decreased insurance premiums. 
The school district's insurer should be consulted to see if premium reductions are 
available, and to see if special enhancements are required in order to avoid paying a 
premium for insurance. For those school districts that self-insure, enhanced wind 
resistance should result in a reduction of future payouts.



6.6 PRIORITIES, COSTS, AND BENEFITS:  EXISTING SCHOOLS

Prior to evaluating existing schools for risk from high winds and beginning the risk 
reduction design process, it is first necessary to consider the priorities, costs, and 
benefits of potential risk reduction measures. These factors, as discussed below, 
should be considered within the context of performance-based wind design as 
discussed in Section 2.12.3. 

 
6.6.1 Priorities

In prioritizing work at existing schools, an assessment should be made on all schools 
within the district to ascertain which schools are vulnerable to damage and therefore 
most in need of remedial work. As part of the assessment, the nature of the 
vulnerability and the needed remedial work should be identified at the various 
schools. In making the district-wide assessment, all applicable hazards should be 
assessed and the needs prioritized. For some districts or some schools within a given 
district, the high priority work may be related to wind, or it may be related to one of 
the other hazards. In some instances, the same remedial work item can mitigate wind 
and other hazards. For example, strengthening the roof deck attachment can 
improve both wind and seismic resistance. 

School districts located in following areas are in greatest need of assessing their 
schools (listed in descending order of priority): hurricane-prone regions and school 
districts outside of hurricane-prone regions that have schools that will be used for 
emergency response after a storm; tornado-prone regions; areas where the basic wind 
speed is in excess of 90 mph (the priority increases as the basic wind speed increases); 
and areas where the basic wind speed is 90 mph or less.
For school districts in hurricane-prone regions, the first priority needs to be given to 
those schools that will be used as hurricane shelters. Other priorities are as discussed 
at the beginning of Section 6.5.1.

For school districts in tornado-prone regions, the first priority needs to be given to 
occupant protection (see Section 6.16). Other priorities are the same as discussed at 
the beginning of Section 6.5.1.
For all other school districts, the priorities are the same as discussed at the 
beginning of Section 6.5.1.

In some instances, perhaps all the funds available for the year for remedial work will 
be spent at one school. In other instances, perhaps the available funds will be used 
for remedial work at several different schools.
See Section 6.17 for specific remedial work guidance.


6.6.2 Cost, Budgeting, and Benefits

Wind-resistance improvements would ideally address all elements in the load path 
from the building envelope to the structural system and into the ground. (Load path 
is discussed in Section 6.8.2 under "Step 3:  Detailed Design"); however, this approach 
can be very expensive if there are many inadequacies throughout the load path. The 
maximum return on dollars invested for wind-resistance improvements is typically 
achieved by performing work related to the building envelope. Obviously if there are 
serious structural deficiencies that could lead to collapse during strong storms, these 
types of deficiencies should receive top priority; however, this scenario is infrequent. 
Because elements of the building envelope are the building components that are 
most likely to fail in the more commonly occurring moderate wind speed events, 
strengthening these elements will avoid damage during those storms. Of course, if a 
storm approaching a design level event occurs, in this scenario, the building 
envelope will remain attached to the structure, but a structural element may fail. For 
example, if the connections between the roof joists and bearing walls are the weak 
link, the roof covering will remain attached to the roof deck and the deck will remain 
attached to the joists, but the entire roof structure will blow off because the joists will 
detach from the wall. Although loss of the entire roof structure is more catastrophic 
than the loss of just the roof covering, much stronger events are typically required to 
cause structural damage. Hence, on a school district-wide level, strengthening 
building envelopes can result in maximum return on funds spent on wind-resistance 
improvements. Of course, for a specific school, the actual scope of wind-resistance 
work should be tailored for that school, commensurate with the findings from the 
evaluation (as discussed in Section 6.6.1) and the benefit/cost analysis (as discussed 
in below under "Benefits").

Costs can be minimized if wind-resistance improvements are executed as part of 
planned repairs or replacement. For example, if the roof deck is inadequately 
attached in the perimeter and corners, and the roof covering has another 10 years of 
remaining service life, it would typically be prudent to hold off performing deck 
attachment upgrade until it is necessary to replace the roof covering. Then, as part of 
the reroofing work, the existing roof system could be torn off, the deck reattached, 
and the new membrane installed.5 With this approach, the full service life of the roof 
membrane (and, hence, its full economic value) is achieved.

Budgeting. As it is with new construction, it is important for the school district to give 
consideration to wind enhancement costs early in the development of a major 
repair/renovation project (see discussion in Section 6.5.2).
Benefits. The benefits for spending money and effort related to wind resistance of 
existing schools are the same as described for new schools in Section 6.5.2.




6.7 EVALUATING SCHOOLS FOR RISK FROM HIGH WINDS

To evaluate risk for wind storms other than tornadoes, the following steps are 
recommended:

¥ Step 1: Determine the basic wind speed from ASCE 7. As the basic wind speed 
increases beyond 90 mph, the risk of damage increases and it continues to 
increase as the speed increases. To compensate for the increased risk of damage, 
design, construction and maintenance enhancements are recommended (see 
Section 6.8). 

¥ Step 2: For schools not located in hurricane-prone regions, 
determine if the school will be used for emergency response after 
a storm (e.g., temporary housing, food or clothing distribution, 
or a place where people can fill out forms for assistance). If so, 
refer to the design, construction, and maintenance 
enhancements recommended for schools in hurricane-prone 
regions (see Section 6.15).

¥ Step 3: For schools in hurricane-prone regions, determine if the 
school will be used for a hurricane shelter and/or for emergency 
response after a storm. If so, refer to the design, construction, and 
maintenance enhancements recommended in Section 6.15. 

¥ Step 4: For existing schools, evaluate the wind resistance of the building. The 
resistance will be a function of its original design and construction, various 
additions or modifications, and condition of building components (which may 
have weakened due to deterioration or fatigue).

 As a first step, calculate the wind loads on the school using ASCE 7 and compare 
these loads with the loads that the school was originally designed for. (The 
original design loads may be noted on the contract drawings. If not, determine 
what building code or standard was used to develop the original design loads and 
calculate the loads using that code or standard.) If the original design loads are 
significantly lower than current loads, upgrading the load resistance of the 
building envelope and/or structure should be considered (see Section 6.6.2). 
(Note:  An alternative to comparing current loads with original design loads is to 
evaluate the resistance of the existing school as a function of the current loads to 
determine what elements are highly overstressed.)

 As a second step, perform a field investigation to evaluate the primary building 
envelope elements and structural system elements to determine if the school was 
generally constructed as indicated on the original contract drawings. As part of 
the investigation, the primary elements should be checked for deterioration. Load 
path continuity should also be checked.
 The above evaluations will allow development of a vulnerability assessment that can 
be used along with the site's wind regime to assess the risk. See Section 6.17 for 
remedial work recommendations.


6.7.1 Tornadoes  

Neither the IBC or ASCE 7 require buildings (including schools) to be designed for 
tornadoes, nor are occupant shelters required in buildings (including schools) 
located in tornado-prone regions. Because of the extremely high pressures and 
missile loads that tornadoes can induce, constructing tornado-resistant schools is 
extremely expensive. Therefore, when consideration is voluntarily given to tornado 
design, the emphasis typically is on occupant protection, which is achieved by 
"hardening" portions of a school for use as safe havens.

In this manual, the term "tornado-prone regions" refers to those areas of the U.S. 
where the number of recorded F3, F4, and F5 tornadoes per 3,700 square miles is six 
or greater (see Figure 6-2). However, a school district may decide to use other 
frequency values (e.g., 1 or greater, 16 or greater, or greater than 25) in defining 
whether or not the district is in a tornado-prone area. In this manual, tornado 
shelters are recommended for schools in tornado-prone regions. 
FEMA 361, Design and Construction Guidance for Community Shelters, includes a 
comprehensive risk assessment procedure that designers can use to assist school 
districts in determining whether a tornado shelter should be included as part of a 
new school. See Section 6.16 for design of tornado shelters.
Where the number of recorded F3, F4, and F5 tornadoes per 3,700 square miles is one 
or greater, if the school does not have a tornado shelter, the best available refuge 
areas should be identified as discussed in Section 6.16.


6.7.2 Portable Classrooms 
 
Unless portables are designed and constructed (including anchorage to the ground) 
to meet the same wind loads as the main school building, students and faculty should 
be considered at risk during high winds. Therefore, portables should not be occupied 
when high winds are forecast (even though the forecast speeds are well below design 
wind conditions for the main building). Also, during winds that are well below 
design wind conditions, it should be recognized that wind-borne debris from 
disintegrating portables could impact and damage the main school building and/or 
nearby residences.




6.8 RISK REDUCTION DESIGN METHODS
  
The keys to enhanced wind performance are devoting sufficient attention to design, 
construction contract administration, construction, maintenance, and repair. Of 
course, it is first necessary for the school district to budget sufficient funds for this 
effort (see Sections 6.5.2 and 6.6.2). This section provides an overview of these 
elements:

6.8.1 Siting

Where possible, a school should not be located in Exposure D. Locating the facility 
on a site in Exposure C or preferably in Exposure B would decrease the wind loads. 
Also, where possible, avoid locating a school on an escarpment or upper half of a hill. 
Otherwise, if the school is located on an escarpment or upper half of a hill, the 
abrupt change in the topography would result in increased wind loads. When siting 
on an escarpment or upper half of a hill is necessary, the ASCE 7 design procedure 
accounts for wind speed-up associated with this abrupt change in topography.
Trees in excess of 6 inches in diameter, poles (e.g., light fixture poles, flag poles, 
power poles), or towers (e.g., electrical transmission and communication towers) 
should not be placed near the school. Blow-down of large trees, poles, and towers can 
severely damage a school and injure occupants.
Providing at least two means of site egress is prudent for all schools, but is 
particularly important for schools used for hurricane shelters and emergency 
response after a storm. Two means of egress facilitate emergency vehicles that need to 
reach or leave the site. With multiple site egress roads, if one route becomes blocked 
by trees or other debris or by floodwaters, another access route should be available.
To the extent possible, site portable classrooms so that, if they disintegrate during a 
storm that approaches from the prevailing wind direction, debris will avoid 
impacting the main school building and residences. Debris can travel in excess of 
300 feet. Destructive winds from hurricanes and tornadoes can approach from any di-
rection. These storms can also throw debris much farther.


6.8.2 School Design 

Good wind performance depends on good design (including detailing and 
specifying), materials, application, maintenance, and repair. A significant 
shortcoming of any of these five elements could jeopardize the performance of a 
school against wind. Design, however, is the key element to achieving good 
performance of a school against wind.  Design inadequacies frequently cannot be 
compensated for by the other four elements. Good design, however, can compensate 
for other inadequacies to some extent.

Step 1: Calculate Loads

Calculate loads on the main wind-force resisting system (MWFRS; i.e., the primary 
structural elements such as beams, columns, shear walls, and diaphragms that 
provide support and stability for the overall building), the building envelope, and 
rooftop equipment in accordance with ASCE 7 or the local building code, whichever 
procedure results in the highest loads.6 The importance factor for most schools will 
be required to be 1.15. For schools with an occupant load of 250 or less and not 
intended for use as shelters, a 1.00 importance factor is permitted; however, a value of 
1.15 is recommended for all schools. 

Uplift loads on roof assemblies can also be determined from Factory Mutual Global 
(FMG) Data Sheets. In some instances, the loads derived from ASCE 7 or the local 
code may exceed those derived from FMG, but, in other cases, the FMG loads may be 
higher. If the school is FMG-insured, and the FMG-derived loads are higher than 
those derived from ASCE 7 or the building code, the FMG loads should govern; 
however, if the ASCE 7 or code-derived loads are higher than those from FMG, the 
ASCE 7 or code-derived loads should govern (whichever procedure results in the 
highest loads). 

Step 2: Determine Load Resistance 

After loads have been determined, it is necessary to determine a reasonable safety 
factor (when using allowable stress design) or reasonable load factor (when using 
strength design). For building envelope systems, a minimum safety factor of two is 
recommended; for anchorage of exterior-mounted mechanical, electrical and 
communications equipment (such as satellite dishes), a minimum safety factor of 
three is recommended. 

For structural members and many cladding elements, load resistance can be 
determined by calculations, based on test data. For other elements (such as most 
types of roof coverings), load resistance is primarily obtained from system testing.
Load resistance criteria need to be given in contract documents. For structural 
elements, the designer of record typically accounts for load resistance by indicating 
the material, size, spacing, and connection of elements. For nonstructural elements, 
such as roof coverings or windows, the load and safety factor can be specified. In this 
case, the specifications should require the contractor's submittals to show that the 
system will meet the load resistance criteria. This performance specification 
approach is necessary if, at the time of design, it is unknown who will manufacture 
the system.

Regardless of which approach is used, it is important that the designer of record 
ensure that it can be demonstrated that the structure, nonstructural building 
envelope, and exterior-mounted mechanical, electrical, and communications 
equipment have sufficient strength to resist design wind loads.

Step 3: Detailed Design

Design, detail, and specify the structural system, building envelope, and exterior-
mounted mechanical, electrical, and communications equipment to meet the 
factored design loads (based on appropriate analytical or test methods) and as 
appropriate to respond to the risk assessment discussed in Section 6.7.
As part of the detailed design effort, load path continuity should be clearly indicated 
in the contract documents. Load paths need to accommodate design uplift, racking, 
and overturning loads. Load path continuity obviously applies to MWFRS elements, 
but it also applies to building envelope elements. Figure 6-19 shows a load path 
discontinuity between a piece of HVAC equipment and its equipment curb. Figure 6-
20 illustrates the load path concept. 

Step 4: Durability

Because some locales have very aggressive atmospheric corrosion (such as schools 
located near oceans), special attention needs to be given to specification of adequate 
protection for ferrous metals, or specify alternative metals such as stainless steel. 
Corrosion Protection for Metal Connectors in Coastal Areas, FEMA Technical Bulletin 8-96, 
August 1996, contains information on corrosion protection. Attention also needs to 
be given to dry rot avoidance, for example, by specifying preservative-treated wood.  
Appendix J of the Coastal Construction Manual, FEMA 55, Third Edition, 2000, presents 
information on wood durability.

Durable materials are particularly important for components that are concealed, 
which thereby prohibit knowing that the component is in imminent danger of 
failing.  
Special attention also needs to be given to details. For example, details that do not 
allow water to stand at connections or sills are preferred. Without special attention to 
material selection and details, the demands on maintenance and repair will be 
increased, along with the likelihood of failure of components during high winds.

Step 5: Rain Penetration

Although prevention of building collapse and major building damage is the primary 
goal of wind-resistant design, consideration should also be given to minimizing 
water damage and subsequent development of mold from penetration of wind-driven 
rain. To the extent possible, non-load bearing walls and door and window frames 
should be designed in accordance with rain-screen principles. With this approach, it 
is assumed that some water infiltration will occur. The water is intercepted in an air-
pressure equalized cavity that provides drainage from the cavity to the outer surface of 
the building. See Sections 6.11.3 and 6.13.3, and Figure 6-47 for further discussion and 
an example. Further information on the rain-screen principle can be found in Facts 
and Fictions of Rain-Screen Walls, M.Z. Rousseau, Construction Canada, 1990.  
In conjunction with the rain-screen principle, it is desirable to avoid using sealant as 
the first line of defense against water infiltration. When joints are exposed, obtaining 
long-lasting watertight performance is difficult because of the complexities of sealant 
joint design and application.


6.8.3 Peer Review

If the design team's wind design expertise and experience is limited, wind design 
input and/or peer review should be sought from a qualified individual(s). The design 
input or peer review could be for the entire school or for specific components such as 
the roof or glazing systems that are critical and/or beyond the design team's 
expertise.  
Regardless of the design team's expertise and experience, peer review should be 
considered when the school:

¥ is located in an area where the basic wind speed is greater than 90 mph (peak gust)
¥ will be used for emergency response after a storm
¥ will be used for a hurricane shelter
¥ will incorporate a tornado shelter


6.8.4 Construction Contract Administration

After a suitable design is complete, the design team should ensure the design intent 
is achieved during construction. The key elements of construction contract 
administration are submittal reviews and field observations, as discussed below.
Submittals. The specifications need to stipulate the submittal requirements. This 
includes specifying what systems require submittals (e.g., windows) and test data 
(where appropriate). Each submittal should demonstrate development of a load path 
through the system and into its supporting element. For example, a window submittal 
should show that the glazing has sufficient strength, its attachment to the frame is 
adequate, and the attachment of the frame to the wall is adequate.
During submittal review, it is important for the designer of record to be diligent in 
ensuring that all required submittals are submitted and that they include the 
necessary information. The submittal information needs to be thoroughly checked to 
ensure its validity. For example, if a test method used to demonstrate compliance with 
the design load appears erroneous, the test data should be rejected unless the 
contractor can demonstrate the test method was suitable.
Field Observations. It is recommended that the design team analyze the design to 
determine which elements are critical to ensuring high-wind performance. The 
analysis should include the structural system and exterior-mounted electrical 
equipment, but it should focus on the building envelope and exterior-mounted 
mechanical and communications equipment. After determining the list of critical 
elements to be observed, observation frequency needs to be determined. Observation 
frequency will depend on the magnitude of the results of the risk assessment 
described in Section 6.7, complexity of the facility, and the competency of the general 
contractor, subcontractors, and suppliers.

See Section 6.15.8 for schools located in hurricane-prone regions.

6.8.5 Post-occupancy Inspections, Periodic Maintenance, Repair, and Replacement

The design team should advise the school administration of the importance of 
periodic inspections, maintenance, and timely repair. It is important for the 
administration to understand that, over time, a facility's wind-resistance will degrade 
due to exposure to weather unless it is periodically maintained and repaired.  
The building envelope and exterior-mounted equipment should be inspected once a 
year by persons knowledgeable of the systems/materials they are inspecting. Items 
that require maintenance, repair, or replacement should be documented and 
scheduled for work. [Note:  The deterioration of glazing is often overlooked. After 
several years of exposure, scratches and chips can become extensive enough to 
weaken the glazing.]

The goal is to repair or replace items before they fail in a storm. This approach is less 
expensive than waiting for failure and then repairing the failed components and 
consequential damages.

If unusually high winds occur, a special inspection is recommended. The purpose of 
the inspection is to assess if the strong storm caused damage that needs to be 
repaired to maintain building strength and integrity. In addition to inspecting for 
obvious signs of damage, the inspector should determine if cracks or other openings 
have developed that allow water infiltration, which could lead to corrosion or dry rot 
of concealed components.

See Section 6.15.9 for schools located in hurricane-prone regions.




6.9 STRUCTURAL SYSTEMS

Based on post-storm damage evaluations, with the exception of tornado events, the 
structural systems (i.e., MWFRS and structural components such as roof decking) of 
school buildings have typically performed quite well during design wind events. 
There have, however, been notable exceptions; in these cases, the most common 
problem has been blow-off of the roof deck, but instances of collapse have also been 
documented (Figure 6-15). The structural problems have primarily been due to lack of 
an adequate load path, with connection failure being a common occurrence. 
Problems have also been caused by reduced structural capacity due to termites, 
workmanship errors (commonly associated with steel decks attached by puddle 
welds), and limited uplift resistance of deck connections in roof perimeters and 
corners (due to lack of code-required enhancement in older editions of the model 
codes).
With the exception of tornado events, structural systems designed and constructed in 
accordance with the IBC should typically offer adequate wind resistance, provided 
attention is given to load path continuity and to material durability (with respect to 
corrosion and termites). However, the greatest reliability is offered by cast-in-place 
concrete. There are no reports of any cast-in-place concrete buildings experiencing a 
significant structural problem during wind events, including the strongest 
hurricanes (Category V) and tornadoes (F5).  
The following design parameters are recommended (see Section 6.15.2 for schools 
located in hurricane-prone regions):

¥ If a pre-engineered structure is being contemplated, special steps should be taken to 
ensure the structure has more redundancy than is typically the case with pre-
engineered buildings.7 Steps should be taken to ensure the structure is not 
vulnerable to progressive collapse in the event a primary bent is compromised or 
bracing components fail.

¥ Exterior load bearing walls of masonry or precast concrete should be designed to 
have sufficient strength to resist external and internal loading of components and 
cladding. CMU walls should have vertical and horizontal reinforcing and grout to 
resist wind loads. The connections of precast concrete wall panels should be 
designed to have sufficient strength to resist wind loads.

¥ For roof decks, specify concrete, steel, or wood sheathing (plywood or oriented 
strand board [OSB]). See Section 6.15.2 for schools located in hurricane-prone 
regions.

¥ For steel roof decks, specify screw attachment rather than puddle welds (screws are 
more reliable and much less susceptible to workmanship problems). See Figures 6-
21 and 6-22. The decking shown in Figure 6-21 was attached with puddle welds. 
However, at most of the welds, there was only superficial bonding of the metal 
deck to the joist, as illustrated at this weld. Only a small portion of the deck near 
the center of the weld area (as delineated by the circle) was well fused to the joist.  

At the weld, shown in Figure 6-22, the deck was well bonded to the joist. When the 
decking blew off due to failure of nearby weak welds, at this location the metal 
decking tore and a portion of it remained attached to the joist. Tearing of the 
decking, rather than debonding, is the desired failure mode, but deck tearing is 
rare due to welding reliability problems. Screw attachment is a more reliable 
attachment method.

¥ For attachment of wood sheathed roof decks, specify screws, or ring-shank or screw-
shank nails in the corner regions of the roof. Where the basic wind speed is 
greater than 90 mph, also specify these types of fasteners for the perimeter regions 
of the roof.

¥ For precast concrete decks, design the deck connections to resist the design uplift 
loads (the dead load of the deck itself is often inadequate to resist the uplift load; 
see Figure 6-23).

¥ For precast Tee decks, design the reinforcing to accommodate the uplift loads in 
addition to the gravity loads. Otherwise, large uplift forces can cause Tee failure 
due to the Tee's own prestress forces after the uplift load exceeds the dead load of 
the Tee (see Figure 6-24).

¥ For schools that have mechanically attached single-ply or modified bitumen 
membranes, refer to the decking recommendations presented in the National 
Research Council of Canada, Institute for Research in Construction, Wind Design 
Guide for Mechanically Attached Flexible Membrane Roofs, B1049, 2004.
¥ If an FMG-rated roof assembly is specified, the roof deck also needs to comply with 
the FMG criteria.



 
6.10 EXTERIOR DOORS

This section addresses primary and secondary egress doors, sectional (garage) doors, 
and rolling doors. See Section 6.15.3 for schools located in hurricane-prone regions.

6.10.1 Loads and Resistance

The IBC requires that the door assembly (i.e., door, hardware, frame, and frame 
attachment to the wall) be of sufficient strength to resist the positive and negative 
design wind pressure. Architects should specify that doors comply with wind load 
testing in accordance with ASTM E 1233. Architects should also specifically design 
the attachment of the door frame to the wall (e.g., specify the type, size, and spacing 
of frame fasteners).

See Section 6.15.3 for schools located in hurricane-prone regions.


6.10.2 Durability 

Where corrosion is problematic, anodized aluminum or galvanized doors and frames, 
and stainless steel frame anchors and hardware are recommended. 
6.10.3Exit Door Hardware
For primary swinging entry/exit doors, exit door hardware is recommended to 
minimize the possibility of the doors being pulled open by wind suction. Exit 
hardware with top and bottom rods offers greater securement than exit hardware that 
latches at the jamb.


6.10.4 Water Infiltration

When heavy rain accompanies high winds (e.g., thunderstorms, tropical storms, and 
hurricanes), it can cause wind-driven water infiltration problems (the magnitude of 
the problem increases with the wind speed). Leakage can occur between the door and 
frame, and frame and wall, and water can be driven between the threshold and door. 
When the basic wind speed is greater than 120 mph, because of the very high design 
wind pressures and numerous opportunities for leakage path development, some 
leakage should be anticipated when design wind speed conditions are approached. 
To minimize infiltration, the following are recommended:

¥ Vestibule. Designing a vestibule is a method to account for the infiltration problem. 
With this approach, both the inner and outer doors can be equipped with 
weatherstripping, and the vestibule itself can be designed to tolerate water. For 
example, water-resistant finishes (e.g., concrete or tile) can be specified and the 
floor can be equipped with a drain.

¥ Door swing. With respect to weatherstripping, out-swinging doors offer an 
advantage compared to in-swinging doors. With out-swinging doors, the 
weatherstripping is located on the interior side of the door, where it is less 
susceptible to degradation. Also, some interlocking weatherstripping assemblies 
are available for out-swinging doors. 
Another challenge with doors is successful integration between the door frame and 
wall. See Section 6.13.3 for discussion of this juncture.  
ASTM E 2112 (Standard Practice for Installation of Exterior Windows, Doors and Skylights) 
provides information pertaining to installation of doors, including the use of sill pan 
flashings with end dams and rear legs (see Figure 6-25). It is recommended that de-
signers use E 2112 as a design resource.


6.10.5 Weatherstripping

A variety of pre-manufactured weatherstripping components are available, including 
drips, door shoes and bottoms, thresholds, and jamb/head weatherstripping. A few 
examples of weatherstripping options are:
¥ Drip. These are intended to shed water away from the opening between the frame 
and door head, and the opening between the door bottom and the threshold (see 
Figures 6-26 and 6-27). Alternatively, a door sweep can be specified (see Figure 6-
28); however, for high-traffic doors, periodic replacement of the neoprene will be 
necessary.

¥ Door shoes and bottoms. These are intended to minimize the gap between the door 
and threshold. Figure 6-27 illustrates a door shoe that incorporates a drip. Figure 
6-29 illustrates an automatic door bottom. Door bottoms can be surface-mounted 
or mortised. For high-traffic doors, periodic replacement of the neoprene will be 
necessary.
¥ Thresholds. These are available to suit a variety of conditions. Thresholds with 
vertical offsets offer enhanced resistance to wind-driven water infiltration. 
However, where Americans with Disabilities Act (ADA)-compliant thresholds are 
required, or at high-traffic doors, the offset is limited. However, at other doors, 
high offsets are preferred.

 Thresholds can be interlocked with the door (see Figure 6-30) or thresholds can have 
a stop and seal (see Figure 6-31). In some instances, the threshold is set directly on 
the floor. Where this is appropriate, specify setting the threshold in butyl sealant 
to avoid water infiltration between the threshold and floor. In other instances, the 
threshold is set on a pan flashing as discussed in Section 6.10.4. If the threshold 
has weep holes, specify that the weep holes should not be obstructed (see Figure 6-
30).

¥ Adjustable jamb/head weatherstripping. This type of jamb/head weatherstripping is 
recommended because these units have wide sponge neoprene that offers good 
contact with the door (see Figure 6-32). The adjustment feature also helps ensure 
good contact, provided the proper adjustment is maintained.
¥ Meeting stile. At the meeting stile of pairs of doors, an overlapping astragal 
weatherstripping offers greater protection than weatherstripping that does not 
overlap.





6.11 NON-LOAD BEARING WALLS, WALL COVERINGS, SOFFITS, AND 
UNDERSIDE OF ELEVATED FLOORS

This section addresses exterior non-load bearing walls and provides guidance for 
interior non-load bearing masonry walls. Exterior wall coverings and soffits, as well as 
the underside of elevated floors, are also discussed.

See Section 6.15.4 for schools located in hurricane-prone regions.



6.11.1 Loads and Resistance

The IBC requires that exterior non-load bearing walls, wall coverings, and soffits (see 
Figure 6-33) have sufficient strength to resist the positive and negative design wind 
pressure. Architects should specify that wall coverings and soffits comply with wind 
load testing in accordance with ASTM E 1233.  

Depending upon wind direction, soffits can experience either positive or negative 
pressure. Besides the cost of repairing damaged soffits, wind-borne soffit debris can 
cause property damage and injuries.

Particular care should be given to the design and construction of exterior non-load 
bearing walls constructed of masonry. Although these walls are not intended to carry 
gravity loads, they must be designed to resist the positive and negative wind loads in 
order to avoid collapse. Because of their great weight, when these types of walls 
collapse, they represent a severe risk to life as shown in Figure 6-14. 
Special consideration should also be given to interior non-load bearing masonry 
walls. Although these walls are not required by building codes to be designed to resist 
wind loads, if glazing is broken, the interior walls could be subjected to significant 
load as the school rapidly becomes fully pressurized. To avoid occupant injury (see 
Figure 6-34), it is recommended that interior non-load bearing masonry walls that are 
adjacent to student areas be designed to accommodate loads exerted by a design wind 
event, using the partially enclosed pressure coefficient. By doing so, wall collapse may 
be prevented if the building envelope is breached. This recommendation is 
applicable to schools in tornado-prone areas that do not have shelter space designed 
in accordance with FEMA 361, to schools located in areas with a basic wind speed 
greater than 120 mph, and to schools that will be used for hurricane shelters.


6.11.2 Durability

Where corrosion is problematic, stainless steel fasteners are recommended for wall 
and soffit systems. For other components (e.g., furring, blocking, struts, and 
hangars), the following are recommended: nonferrous components (such as wood), 
stainless steel, or steel with a minimum of G-90 hot-dipped galvanized coating. In 
addition, if air can freely circulate in a cavity (e.g., above a soffit), access panels are 
recommended so components within the cavity can be periodically observed for 
corrosion.


6.11.3 Wall Coverings

There are a variety of exterior wall covering options. Brick veneer, exterior insulation 
finish systems (EIFS), metal wall panels, and aluminum and vinyl siding have often 
exhibited poor wind performance. Veneers (such as ceramic tile and stucco) over 
concrete and cement-fiber panels and siding have also blown off. Blow-off of wood 
siding and panels is rare.
Figure 6-35 shows brick veneer that was blown off. The bricks were attached to the 
back-up wall with corrugated metal ties. All of the following failure modes are 
commonly found in the vicinity of this type of common failure: 1)The nails pull out 
of the studs (smooth shank nails are typically used, hence they have limited 
withdrawal resistance; 2)The ties do not extend far enough into the mortar joint (i.e., 
the tie is not long enough); 3)Although the ties make contact with the mortar, they 
are not well-bonded to it; 4)The ties are spaced too far apart; and 5)The ties provide 
essentially no resistance to compression. Hence, when a great amount of positive 
pressure is applied to the bricks, the brick joints flex. This flexing weakens the 
mortar joint. Walls that have not had bricks blown away have been found to be 
capable of being deflected with hand pressure. Although they look sound, in this 
condition they are very vulnerable to failure. Good reliable wind performance of brick 
veneer is very demanding on the designer and applicator.
Figure 6-36 shows EIFS blow-off. In this case, the expanded polystyrene (EPS) was 
attached to gypsum board, which was attached to metal studs. The gypsum board 
detached from the studs, which is a common EIFS failure mode. When the gypsum 
board on the exterior side of the studs is blown away, it is common for gypsum board 
on the interior side to also be blown off. This then allows the school to become fully 
pressurized and allows entrance of wind-driven rain. Other common failure modes 
include separation of the EPS from its substrate and separation of the synthetic 
stucco from the EPS. Good reliable wind performance of EIFS is very demanding on 
the designer and applicator. Maintenance of EIFS and associated sealant joints is also 
demanding in order to minimize reduction of EIFS' wind resistance due to water 
infiltration.
Another issue associated with EIFS is the potential for misdiagnosis of the wall 
system. EIFS is sometimes mistaken to be a concrete wall. If school personnel 
believed that an EIFS wall covering was a concrete wall and sought shelter from a 
tornado, instead of being protected by several inches of concrete, only two layers of 
gypsum board (i.e., one layer on each side of the studs) and a layer of EPS would be 
between the occupants and wind-borne debris. The debris could easily penetrate such 
a wall. 

EIFS can also be applied over concrete or CMU. In this scenario, the concrete or 
CMU could provide adequate missile protection provided it was thick enough and 
adequately reinforced. However, with this wall construction, there is still risk of blow-
off of the EIFS. As discussed in Section 6.15.4, if the concrete or CMU is left exposed, 
there is no covering to be blown off.

Wind performance of metal wall panels is highly variable. Performance depends 
upon strength of the specified panel (which is a function of material, panel profile, 
panel width and whether or not the panel is a composite) and the adequacy of the at-
tachment (which can either be by concealed clips or exposed fasteners). A common 
problem is excessive spacing between clips/fasteners. Clip/fastener spacing should 
be specified, along with the specific type and size of fastener to be used. 

Figures 6-13 
and 6-43 illustrate metal wall panel problems.

To minimize water infiltration at metal wall panel joints, it is recommended that 
sealant tape be specified at sidelaps when the basic wind speed is in excess of 90 mph. 
However, end laps should be left unsealed so that moisture behind the panels can 
wick out. End laps should be a minimum of 3 inches (4 inches where the basic wind 
speed is greater than 120 mph) to avoid wind-driven rain infiltration. At the base of 
the wall, a 3-inch (4-inch) flashing should also be detailed, or the panels should be 
detailed to over-lap with the slab or other components by a minimum of 3 inches (4 
inches).
Vinyl siding blow-off is typically caused by nails spaced too far apart and/or the use of 
vinyl siding that has inadequate wind-resistance. Vinyl siding is available with 
enhanced wind resistance features, such as an enhanced nailing hem, greater 
interlocking area, and greater thickness. 
Secondary Protection. Almost all wall coverings permit the passage of some water past 
the exterior surface of the covering, particularly when rain is wind-driven. Hence, 
most wall coverings should be considered as water-shedding, rather than as water-
proofing coverings. To avoid moisture related problems, it is recommended that a 
secondary line of protection with a moisture barrier (such as housewrap or asphalt-
saturated felt) and flashings around door and window openings be provided. 
Designers should specify that horizontal laps of the moisture barrier be installed so 
that water is allowed to drain from the wall (i.e., the top sheet should lap over the 
bottom sheet so that water running down the sheets remains on their outer surface). 
The bottom of the moisture barrier needs to be detailed to allow drainage.
In areas that frequently experience strong winds, enhanced flashing details are 
recommended. Enhancements include use of flashings that have extra-long flanges, 
and use of sealant and tapes. Flashing design should recognize that wind-driven 
water can be pushed vertically. The height to which water can be pushed increases 
with wind speed. Water can also migrate vertically and horizontally by capillary action 
between layers of materials (e.g., between a flashing flange and housewrap). It is 
recommended that designers attempt to determine what type of flashing details have 
successfully been used in the area where the school will be constructed.
If EIFS is specified, it is strongly recommended that it be designed with a drainage 
system that allows for dissipation of water leaks.


6.11.4 Underside of Elevated Floors

If sheathing is applied to the underside of joists or trusses elevated on piles (e.g., to 
protect insulation installed between the joists/trusses), its attachment should be 
specified in order to avoid blow-off. Stainless steel or hot-dip galvanized nails or 
screws are recommended. ASCE 7 does not provide guidance for load determination.




 
6.12 ROOF SYSTEMS

Because roof covering damage has historically been the most frequent and costly type 
of wind damage, special attention needs to be given to roof system design.
Code Requirements. The IBC requires load resistance of the roof assembly to be 
evaluated by one of the test methods listed in IBC's Chapter 15. Architects are 
cautioned that designs that deviate from the tested assembly (either with material 
substitutions or change in thickness or arrangement) may adversely affect the wind 
performance of the assembly. The IBC does not specify a minimum safety factor. 
However, for the roof system, a safety factor of two is recommended. (To apply the 
safety factor, divide the test load by two to determine the allowable design load. 
Conversely, multiply the design load by two to determine the minimum required test 
resistance.)

For metal panel systems, the IBC requires test methods UL 580 or ASTM E 1592. It is 
recommended that architects specify use of E 1592 because it is more likely to give a 
better representation of the system's uplift performance capability. 
Load Resistance. Specifying load resistance is commonly done by specifying a Factory 
Mutual Research (FMR) rating, such as Factory Mutual (FM) 1-75. The first number 
("1") indicates that the roof assembly passed the FMR tests for a Class 1 fire rating. 
The second number ("75") indicates the uplift resistance in psf that the assembly 
achieved during testing. Applying a safety factor of two to this example, this assembly 
would be suitable where the design uplift load is 37.5 psf. 
As previously discussed, because of building aerodynamics, the highest uplift load 
occurs at roof corners. The perimeter has a somewhat lower load; the field of the roof 
has the lowest load. FMG Data Sheets are formatted so that a roof assembly can be 
selected for the field of the roof. That assembly is then adjusted to meet the higher 
loads in the perimeter and corners by increasing the number of fasteners or 
decreasing the spacing of adhesive ribbons by a required amount; however, this 
assumes that the failure is the result of the pulling-out of the fastener from the deck, 
or that failure is in the vicinity of the fastener plate, which may not be the case. Also, 
the increased number of fasteners required by FM may not be sufficient to comply 
with the perimeter and corner loads derived from the building code. Therefore, if FM 
resistance data are specified, it is prudent for the architect to separately specify the 
resistance for the field of the roof (1-75 in the example above), the perimeter (1-130), 
and the corner (1-190).  

Edge Flashings and Copings. Roof membrane blow-off is almost always a result of 
lifting and peeling of the metal edge flashing or coping, which serves to clamp down 
the membrane at the roof edge (see Figure 6-37). Therefore, it is important for the 
architect to carefully consider the design of metal edge flashings, copings, and the 
nailers to which they are attached. ANSI/SPRI ES-1, Wind Design Standard for Edge Systems 
Used in Low Slope Roofing Systems provides general design guidance, including a 
methodology for determining the outward-acting load on the vertical flange of the 
flashing/coping (ASCE 7 does not provide this guidance). A minimum safety factor 
of three for edge flashings, copings, and nailers is recommended for schools. 
ANSI/SPRI ES-1 also includes test methods for assessing flashing/coping resistance. 
For FMG-insured schools, FMR approved flashing should be used and Data Sheet 1-49 
should also be consulted. 
The traditional edge flashing/coping attachment method relies on concealed cleats 
that can deform under wind load and lead to disengagement of the flashing/coping 
(see Figure 6-38) and subsequent lifting and peeling of the roof membrane (as shown 
in Figure 6-11). When a vertical flange disengages and lifts up (as shown in Figure 6-
38), the edge flashing and membrane are very susceptible to failure. Normally, when a 
flange lifts such as shown in Figure 6-38, the failure continues to propagate and the 
metal edge flashing and roof membrane blow off. 

Storm-damage research has revealed that, in lieu of cleat attachment, use of exposed 
fasteners to attach the vertical flanges of copings and edge flashings has been found 
to be a very effective and reliable attachment method (see Figure 6-39). 
If cleats are used for attachment, it is recommended that a bar be placed over the roof 
membrane near the edge flashing/coping as illustrated in Figure 6-40. The purpose 
of the bar is to provide secondary protection against membrane lifting and peeling in 
the event that the edge flashing/coping fails. A robust bar specifically made for bar-
over mechanically attached single-ply systems is recommended. The bar needs to be 
very well anchored to the parapet or deck. Depending upon design wind loads, a 
spacing between 4 and 12 inches on center is recommended. A gap of a few inches 
should be left between each bar to allow for water flow across the membrane. After 
the bar is attached, it is stripped over with a stripping ply.
Gutters. Special design attention needs to be given to uplift attachment of gutters, 
particularly those in excess of 6 inches wide.  Recommendations are provided in 
"Honing in on hangars," Professional Roofing, Thomas L. Smith, October 2002, pp. 32 
(available on-line at www.nrca.net).

Roof System Performance. Storm-damage research has shown that sprayed 
polyurethane foam and liquid-applied roof systems are very reliable high-wind 
performers. If the substrate to which the foam or liquid-applied membrane was 
applied does not lift, it is highly unlikely that the sprayed polyurethane foam (SPF) or 
the liquid-applied membrane will blow-off. Both systems are also more tolerant of 
missiles than other systems. Built-up roofs (BURs) and modified bitumen systems 
have also demonstrated good wind performance provided the edge flashing/coping 
does not fail (edge flashing/coping failure is common). The exception is aggregate 
surfacing, which is prone to blow-off (see Figure 6-11). Modified bitumen adhered to 
a concrete deck has demonstrated excellent resistance to progressive peeling after 
blow-off of the metal edge flashing. Metal panel performance is highly variable. Some 
systems are very wind-resistant, while others are quite vulnerable. 
Of the single-ply attachment methods, the paver-ballasted and fully adhered methods 
are the least problematic. Systems with aggregate ballast are prone to blow-off, unless 
care is taken in the design of the size of aggregate and the parapet height (see Figure 
6-8). Performance of protected membrane roofs (PMRs) with factory-applied 
cementitious coating over insulation boards is highly variable. When these boards 
are installed over a loose-laid membrane, it is critical that an air retarder be 
incorporated to prevent the membrane from ballooning and disengaging the boards. 
ANSI/SPRI RP-4 (which is referenced in the IBC) provides wind guidance for 
ballasted systems using aggregate, pavers, and cementitious-coated boards. 
The National Research Council of Canada, Institute for Research in Construction's 
Wind Design Guide for Mechanically Attached Flexible Membrane Roofs, B1049 (2004) provides 
recommendations related to mechanically attached single-ply and modified 
bituminous systems. B1049 is a very comprehensive wind design guide and includes 
discussion of air retarders, which can be effective in reducing membrane flutter, in 
addition to their beneficial use in ballasted single-ply systems. When a mechanically 
attached system is specified, careful coordination with the structural engineer with 
respect to selection of deck type and thickness is important. If a steel deck is 
specified, it is critical to specify that the membrane fastener rows run perpendicular 
to the steel flanges in order to avoid overstressing attachment of the deck to the deck 
support structure (see Figures 6-41 and 6-42). In Figure 6-42, the flange with 
membrane fasteners carries essentially all of the uplift load because of the deck's 
inability to transfer any significant load to adjacent flanges. Hence, at the joists, the 
deck fasteners on either side of the flange with the membrane fasteners are the only 
connections to the joists that are carrying uplift load. Had the membrane fasteners 
shown in Figure 6-42 been run perpendicular to the deck flanges, each of the 
fasteners connecting the deck to the joists would have been carrying uplift load. 
Recommendations related to metal panels is provided in "Insights on Metal Roof 
Performance in High-wind Regions," Professional Roofing, Thomas L. Smith, February 
1995, pp. 12 (available on-line at  www.nrca.net).

Parapet Base Flashings. Loads on parapet base flashings were first introduced in the 
2002 edition of ASCE 7. The loads on base flashings are greater than the loads on the 
roof covering if the parapet's exterior side is air-permeable. When base flashing is 
fully adhered, it has sufficient wind resistance in most cases. However, when base 
flashing is mechanically fastened, typical fastening patterns may be inadequate, 
depending upon design wind conditions (see Figure 6-43). Therefore, it is imperative 
that base flashing loads be calculated and attachments be designed to accommodate 
the loads. It is also important for designers to recognize and specify different 
attachment spacings in parapet corner regions versus regions between corners. 
Further discussion is provided in "Detailing ASCE 7's changes," Professional Roofing, 
Thomas L.  Smith, July 2003, pp. 26 (available on-line at www.nrca.net).

Lightning Protection Systems. When not adequately integrated into a roof system, a 
lightning protection system can become detached from the roof during high winds. 
The detached system can damage the roof covering (see Figure 6-44). In addition, a 
detached system is no longer capable of providing lightning protection. Most 
manufacturers of lightning protection systems and most roofing manufacturers 
provide vague or inadequate details for securing a lightning protection system to a 
roof.  

During prolonged high winds, repeated slashing of the membrane by loose 
conductors ("cables") and puncturing by air terminals can result in lifting and 
peeling of the membrane. It is, therefore, important to adequately design the 
attachment of the lightning protection system. Recommendations pertaining to 
wind-resistant design, and specification and installation of lightning protection 
systems are provided in  "Integrating a Lightning Protection System in a Roof 
System," Thomas L. Smith, 12th International Roofing and Waterproofing 
Conference Proceedings (CD), National Roofing Contractors Association, 2002.
Hurricane-prone Regions. See Section 6.15.5 for schools in hurricane-prone regions.

Tornado-prone Regions. In order to reduce the number of wind-borne missiles, it is 
recommended that aggregate surfacings, pavers, tile, and slate not be specified on 
schools in tornado-prone regions (as defined in Section 6.7.1; see Figure 6-8).





6.13 WINDOWS AND SKYLIGHTS

This section addresses exterior windows and skylights. See Section 6.15.6 for schools 
located in hurricane-prone regions

6.13.1 Loads and Resistance

The IBC requires the window, curtain wall, or skylight assembly (i.e., the glazing, 
frame, and frame attachment to the wall or roof) to have sufficient strength to resist 
the positive and negative design wind pressure (see Figure 6-45). Architects should 
specify that these assemblies comply with wind load testing in accordance with ASTM 
E 1233. It is important to specify an adequate load path and to check its continuity 
during submittal review.

In tornado-prone regions, some school districts may desire to have laminated glazing 
installed at exterior openings in order to provide wind-borne debris protection 
during weak tornadoes. Laminated glazing may also offer protection during strong 
tornadoes, but should not be relied upon for violent tornadoes. Further discussion is 
provided in Section 6.15.6.

6.13.2 Durability

Where corrosion is problematic, anodized aluminum or stainless steel frames and 
stainless steel frame anchors are recommended.
6.13.3Water Infiltration
When heavy rain accompanies high winds (e.g., thunderstorms, tropical storms, and 
hurricanes), it can cause wind-driven water infiltration problems; the magnitude of 
the problem increases with the wind speed. Leakage can occur at the glazing/frame 
interface, at the frame itself, or between the frame and wall. When the basic wind 
speed is greater than 120 mph, because of the very high design wind pressures and 
numerous opportunities for leakage path development, some leakage should be 
anticipated when design wind speed conditions are approached.  
The challenge with windows and curtain walls is successful integration between these 
elements and the walls. To the extent possible, detailing of the interface between the 
wall and the window or curtain wall units should rely on sealants as the secondary 
line of defense against water infiltration, rather than making the sealant the primary 
protection.  

When designing joints between walls and windows and curtain wall units, consider 
the shape of the sealant joint (i.e., a square joint is typically preferred) and the type of 
sealant to be specified. The sealant joint should be detailed so the sealant is able to 
bond on only two opposing surfaces (i.e., a backer rod or bond-breaker tape should 
be specified). For concealed sealants, butyl is recommended. For exposed sealants, 
polyurethane is recommended. During installation, cleanliness of the sealant 
substrate is important (particularly if polyurethane or silicone sealants are specified), 
as well as tooling of the sealant. ASTM E 2112 provides guidance on design of sealant 
joints, as well other information pertaining to installation of windows, including the 
use of sill pan flashings with end dams and rear legs (see Figure 6-46). It is 
recommended that designers use ASTM E 2112 as a design resource.
Sealant joints can be protected with a removable stop as illustrated in Figure 6-47. The 
stop protects the sealant from direct exposure to the weather and reduces the wind-
driven rain demand on the sealant.

Where water infiltration protection is particularly demanding and important, it is 
recommended that on-site water infiltration testing in accordance with ASTM E 1105 
be specified.


6.14 EXTERIOR-MOUNTED MECHANICAL, ELECTRICAL, AND 
COMMUNICATIONS EQUIPMENT

Exterior-mounted mechanical (e.g., exhaust fans, HVAC units, relief air hoods, boiler 
stacks), electrical, and communications equipment (e.g., light fixtures, antennae, 
satellite dishes) are often damaged during high winds. Damaged equipment can im-
pair the use of the school, the equipment can become missiles, and water can enter 
the facility where equipment was displaced (see Figures 6-19 and 6-48).
Problems typically relate to inadequate equipment anchorage, inadequate strength of 
the equipment itself, and corrosion.


6.14.1 Loads and Attachment

Rooftop Equipment. Criteria for determining loads on rooftop equipment were added 
to the 2002 edition of ASCE 7. A minimum safety factor of three is recommended for 
the design of equipment anchorage.

To anchor membrane fans, small HVAC units, and relief air hoods, the following 
minimum prescriptive attachment schedule is recommended:

¥ For curb-mounted units, specify #14 screws with gasketed washers.
¥ For curbs with sides less than 12 inches, specify one screw at each side of the curb.
¥ For curbs between 12 inches and 24 inches, specify two screws per side. 
¥ For curbs between 24 inches and 36 inches, specify three screws per side. 
¥ For units that have flanges attached directly to the roof, attachment with #14 pan-
head screws is recommended. A minimum of two screws per side, with a maximum 
spacing of 12 inches on center is recommended.
Figure 6-49 illustrates the use of supplemental securement straps to anchor 
equipment. The supplemental attachment was marginal; the straps were too light and 
the fasteners used to secure them were corroded. This illustrates the validity of the 
supplemental securement, and it also illustrates the need to execute the securement 
with attention to detail. In lieu of one screw at each end of the strap, two side-by-side 
screws offer a stronger and more reliable connection (this of course requires a 
slightly wider strap).

Electrical and Communications Equipment.  Damage to exterior-mounted electrical 
equipment is infrequent, in large part, because of the small size of most equipment 
(e.g., disconnect switches). Exceptions are communication masts (see Figure 6-50), 
surveillance cameras, service masts, and satellite dishes. These failures are typically 
caused by failure to perform wind load calculations and anchorage design. Service 
mast failure is typically caused by collapse of overhead power lines; this can be 
avoided by underground service. Where overhead service is provided, it is 
recommended that the service mast not penetrate the roof. Otherwise, a downed 
service line could pull the mast and rupture the roof membrane.

ASCE 7 provides load calculation criteria for trussed towers. The ASCE 7 criteria are 
consistent with ANSI/EIA/TIA-222-E. The ASCE 7 approach is a simplified procedure. 
The IBC allows use of either approach. ASCE 7 does not provide guidance for on-site 
power distribution poles nor for light fixture poles. However, the National Electrical 
Safety Code, ANSI/C2 provides guidance for determining wind loads on power poles. 
The AASHTO Standard Specification for Structural Support for Highway Signs, Luminaries and 
Traffic Signals provides guidance for determining wind loads on light fixture poles.
See Section 6.8.1 regarding siting of light fixture poles, power poles, and electrical 
and communications towers.



6.14.2 Equipment Strength
It is common for equipment components such as fan cowlings and access panels to 
be blown off during storms. Design of these elements is the responsibility of the 
equipment manufacturer. Although poor equipment performance has been 
documented, manufacturers have not offered enhanced equipment for high-wind 
regions. Therefore, it is incumbent upon the architect/engineer to give special 
design attention to equipment strength.

Damage investigations have revealed that cable tie-downs have been effective in 
securing fan cowlings when a sufficiently strong cable and anchor details were used 
(see Figure 6-51). For fan cowlings less than 4 feet in diameter, 1/8-inch diameter 
stainless steel cables are recommended. For larger cowlings, use 3/16-inch diameter 
cables.  When the basic wind speed is 120 mph or less, specify two cables. Where the 
basic wind speed is greater than 120 mph, specify four cables. (As an alternative to 
cables, heavy stainless steel straps could be screwed to the cowling and curb.) To 
minimize leakage potential at the anchor point, it is recommended that the cables be 
anchored to the equipment curb (rather than anchored to the roof deck). The 
attachment of the curb itself also needs to be designed and specified.  
To minimize blow-off of equipment access panels, job-site modification will typically 
be necessary (such as the attachment of hasps and locking devices such as a 
carabineer). The modification details will need to be tailored for the equipment, 
which may necessitate detail design after the equipment has been delivered to the job 
site.  Alternatively, factored loads on the equipment could be specified, along with the 
requirement for the manufacturer to demonstrate compliance with the load 
requirement.


6.14.3 Durability  

To avoid corrosion-induced blow-off, it is recommended that exterior-mounted 
mechanical, electrical, and communications equipment be nonferrous, stainless 
steel, or steel with minimum G-90 hot-dip galvanized coating for the equipment itself, 
equipment stands, anchors, and fasteners. When equipment with enhanced 
corrosion protection is not available, the designer should advise the school district 
that periodic equipment maintenance and inspection is particularly important to 
avoid advanced corrosion and subsequent equipment damage during a windstorm.
The recommendations given in Sections 6.8 through 6.14 are summarized in Table 6-
1.




6.15 SCHOOLS LOCATED IN HURRICANE-PRONE REGIONS 


The IBC, through ASCE 7, prescribes that exterior glazing in schools in wind-borne 
debris regions be provided with wind-borne debris protection (either by use of 
laminated glass or shutters, as discussed in Section 6.15.6). Schools in hurricane-
prone regions also have to be designed for a 100-year mean recurrence interval wind 
event if they are to be used as shelters. These are the only hurricane-related 
requirements currently in the IBC. These requirements do not provide adequate 
protection to occupants in a school during a hurricane, because the missile 
requirements only pertain to glazing. Hence, a code-compliant school can be 
designed, yet still allow the entrance of missiles through the roof or walls. To account 
for this deficiency, recommendations are given below regarding missile penetration 
through exterior walls and the roof. For a more conservative hurricane shelter, refer 
to FEMA 361.

Publication 4496 by the American Red Cross (ARC) provides information regarding 
assessing existing buildings for use as hurricane shelters. Unless a school has been 
specifically designed for use as a shelter, it should only be used as a last resort and 
only if the school meets the criteria given in ARC 4496.
Schools located in hurricane-prone regions should receive special design attention 
because of the unique characteristics of this type of windstorm. In addition to being 
capable of delivering very high winds, hurricanes can cause strong winds for many 
hours, which can eventually lead to fatigue failure. The direction of the wind can also 
change, thereby increasing the probability that the wind will approach the school at 
the most critical angle. Hurricanes also typically generate a large amount of missiles, 
which can be very damaging to schools and cause injury or death.  
For schools in hurricane-prone regions that will be used for a hurricane shelter 
and/or for emergency response after a storm, the following design parameters are 
recommended (these recommendations are in addition to the recommendations 
previously given in Sections 6.8 through 6.14):

1.   During the design phase, the architect should determine from the school district 
whether or not the school will be designated or used as a shelter or emergency 
response facility. The school should only be used for a shelter if it was designed 
for that purpose.  

2.   For schools in coastal Alaska and other areas that experience frequent high wind 
events (such as parts of Colorado), several of the following recommendations are 
also applicable to these schools, with the exception of the wind-borne debris 
recommendations.


6.15.1 Design Loads  

For the importance factor, use a value of 1.15.


6.15.2 Structural Systems
  
Because of the exceptionally good wind performance that reinforced cast-in-place 
concrete structures offer, a reinforced concrete roof deck and reinforced concrete 
and/or reinforced and fully grouted CMU exterior walls are recommended.  
In order to achieve enhanced missile resistance, the following roof decks are 
recommended, in descending order of preference: cast-in-place concrete, precast 
concrete, and concrete topping over steel decking. For exterior walls, the following 
are recommended: 6-inch (minimum) thick concrete reinforced with #4 rebars at 12 
inches on center each way, or 8-inch (minimum) thick fully grouted CMU reinforced 
with #4 rebars in each cell.


6.15.3 Exterior Doors

For glazing in doors, see the recommendations in Section 6.15.6.

Although the ASCE-7 wind-borne debris provisions only apply to glazing within a 
portion of hurricane-prone regions, it is recommended that all schools that will be 
used for evacuation shelters within the entire hurricane-prone region comply with 
the following recommendation: To minimize the potential of missiles penetrating 
exterior doors and striking people within the school, it is recommended that doors 
without glazing and the unglazed portions of doors with glazing  be designed to 
resist the missile loads specified in ASTM E 1996 and that they be tested in 
accordance with ASTM E 1886. The test assembly should include the door, door frame 
and hardware. Further information on missile resistance of doors is found in FEMA 
361, Design and Construction Guidance for Community Shelters.
6.15.4Non-load Bearing Walls, Wall Coverings, and Soffits  
In order to achieve enhanced missile resistance, the following types of exterior walls 
are recommended: reinforced cast-in-place concrete, or reinforced and fully grouted 
CMU. 

To minimize long-term problems with non-load bearing walls, wall coverings, and 
soffits, it is recommended that non-load bearing exterior walls, wall coverings, and 
soffits be avoided to the extent possible. Reinforced concrete or CMU offers greater 
reliability (i.e., they have no coverings that can be blown off). 

 
6.15.5 Roof Systems

The following types of roof systems are recommended on schools in hurricane-prone 
regions because they are more likely to avoid water infiltration if the roof is hit by 
wind-borne debris.  Also, the following systems are less likely to become sources of 
wind-borne debris:

¥ In tropical climates where insulation is not needed above the roof deck: 1) liquid-
applied membrane over cast-in-place concrete deck, or 2) modified bitumen 
membrane torched directly to cast-in-place concrete deck.
¥ Install a secondary membrane over a concrete deck (if another type of deck is 
specified, a cover board may be needed over the deck). Seal the secondary 
membrane at perimeters and penetrations. Specify a minimum 2-inch thick rigid 
insulation and a layer of 5/8-inch thick glass mat gypsum roof board over the 
secondary membrane to absorb missile energy. If the primary membrane is 
punctured during a storm, the secondary membrane should provide watertight 
protection unless the roof is hit with missiles of very high energy. A modified 
bitumen membrane is recommended for the primary membrane because of its 
enhanced resistance to puncture by small missiles.
¥ For an SPF roof system over a concrete deck, specify that the foam be a minimum of 
3 inches thick to avoid missile penetration through the entire layer of foam.
¥ For a PMR, it is recommended that pavers weighing a minimum of 22 psf be 
specified. In addition, base flashings should be protected with metal. Parapets are 
recommended at roof edges. The parapet should be at least 3 feet high or higher if 
so indicated by ANSI/SPRI RP-4. Note: If the basic wind speed exceeds 130 mph, a 
PMR is not recommended on schools in hurricane-prone regions.
¥ For structural metal roof panels with concealed clips, it is recommended that 
mechanically seamed ribs spaced at 12 inches on center over a concrete deck be 
specified. If a steel deck is specified, specify a self-adhering modified bitumen 
membrane and 3-inch thick rigid insulation, followed by the metal panels 
installed on wood nailers. At the self-adhering membrane laps, specify metal strips 
over the deck where the laps do not occur over the deck ribs, or specify a suitable 
cover board between the deck and self-adhering membrane. If the metal panels are 
punctured during a storm, the secondary membrane should provide watertight 
protection unless the roof is hit with missiles of very high energy. Note:  
Architectural metal panels are not recommended on schools in hurricane-prone 
regions.

In order to avoid the possibility of roofing debris blowing off and striking people 
arriving at the school during the storm, the following types of roof coverings are not 
recommended:  aggregate surfacings (either on BUR [shown in Figure 6-11], single-
plies [shown in Figure 6-8] or SPF), lightweight concrete pavers, cementitious-coated 
insulation boards, slate, and tile (see Figure 6-52). Wind-borne debris from heavy roof 
coverings such as tiles have great potential to cause serious injury to people arriving 
at a school during a hurricane or other high wind event.

Because mechanically attached and air-pressure equalized single-ply membrane 
systems are susceptible to massive progressive failure after missile impact (see Figure 
6-53), these systems are not recommended on schools in hurricane-prone regions. 
Fully adhered single-ply membranes are also very vulnerable to missiles (see Figure 6-
54); therefore, they also are not recommended unless they are ballasted with pavers. 


6.15.6 Windows and Skylights

ASCE 7 requires the use of impact-resistant glazing (i.e., laminated glass) or shutters 
in wind-borne debris regions. ASCE 7 refers to ASTM E 1996 for missile loads and to 
ASTM E 1886 for the test method to be used to demonstrate compliance with the E 
1996 load criteria. In addition to testing for impact resistance, the window unit is 
subjected to pressure cycling after missile impact to evaluate whether or not the 
window can still resist wind loads.
If wind-borne debris glazing protection is provided by shutters, the glazing is still 
required by ASCE 7 to meet the positive and negative design air pressures.
For those schools that desire to provide blast-resistant glazing, the windows and 
glazed doors can be designed to accommodate wind pressure, missile loads, and blast 
pressure. However, the window and door units need to be tested for missile loads and 
cyclic air pressure, as well as for blast. A unit that meets blast criteria will not 
necessarily meet the E 1996 and E 1886 criteria, and vice versa. 
With the advent of building codes requiring glazing protection in wind-borne debris 
regions, a variety of shutter designs have entered the market. Figure 6-55 illustrates an 
effective shutter. A metal track was permanently mounted to the wall above and below 
the window frame. Upon notification of an approaching hurricane, the metal shutter 
panels were inserted into the frame and locked into position with wing nuts. 
Shutters typically have a lower initial cost than laminated glass. However, unless the 
shutter is permanently anchored to the school (e.g., an accordion shutter), space will 
be needed to store the shutters. Also, when a hurricane is forecast, costs will also be 
incurred each time shutters are installed and removed afterward. To avoid the 
difficulty of installing shutters on upper-level glazing, motorized shutters could be 
specified, although laminated glass may be more economical in these locations. 


6.15.7 Emergency Power

Schools intended for use as shelters and/or emergency response after a storm should 
be equipped with an emergency generator.


6.15.8 Construction Contract Administration

It is important for the school district to obtain the services of a professional 
contractor who will execute the work described in the contract documents in a 
diligent and technically proficient manner.  
The frequency of field observations and extent of special inspections and testing 
should be greater than those employed on schools that are not designated as shelters.


6.15.9 Periodic Inspections, Maintenance, and Repair

The recommendations previously given for periodic and post-storm inspections, 
maintenance, and repair are critically important for schools used as shelters and 
emergency response after a storm because, if failure occurs, the risk of injury or death 
to occupants is great, and the needed continued operation of the school would be 
jeopardized.
The recommendations given in Section 6.15 are summarized in Table 6-2.  These 
recommendations are in addition to those given in Sections 6.8 to 6.14, as 
summarized in Table 6-1.




 
6.16 DESIGN FOR TORNADO SHELTERS

Tornado risk assessment and tornado-prone regions were discussed in Section 6.7 
and the cost of tornado shelters was discussed in Section 6.5.2. Following up on those 
discussions, strong and violent tornadoes produce wind speeds that are substantially 
greater than those delivered by the strongest hurricanes; hence, the wind pressures 
that these tornadoes exert on buildings is tremendous and far exceed the minimum 
pressures required by building codes. In addition, strong and violent tornadoes can 
generate very powerful missiles (see Figure 6-56), including vehicles. The missile 
sticking out of the roof in the foreground of Figure 6-56 is a double 2-inch by 6-inch. 
The portion sticking out of the roof is 13 feet long. It penetrated a ballasted ethylene 
propylene diene monomer (EPDM) membrane and approximately 3 inches of 
polyisocyanurate roof insulation and the steel roof deck. The missile laying on the 
roof just beyond is 2 inches by 10 inches by 16 feet long. 
Missile loads that are used for the design of tornado shelters are significantly greater 
than the missile loads used for the design of glazing protection in wind-borne debris 
regions of hurricane-prone regions.

As discussed in Section 6.5.2, FEMA 361, Design and Construction Guidance for Community 
Shelters, includes software for assessing the benefit/cost ratio of incorporating 
specially designed tornado shelters within schools. In addition, it includes 
comprehensive information regarding the design of shelters. If shelter design is 
contemplated, use of FEMA 361 is recommended. 

Existing Schools without Tornado Shelters. Where the number of recorded F3, F4,  and 
F5 tornadoes per 3,700 square miles is one or greater (see Figure 6-2), if the school 
does not have a tornado shelter, the best available refuge areas should be identified. 
FEMA 431, Tornado Protection, Selecting Refuge Areas in Buildings provides useful 
information for school administrators, and for architects and engineers who perform 
evaluations of existing schools.

To minimize deaths and injuries of students, faculty, and other occupants, it is 
critically important that the best available refuge areas be pre-identified by a qualified 
architect/engineer.8  Once identified, those areas need to be clearly marked so that 
occupants can quickly seek refuge. Don't wait for the arrival of a tornado on the 
school grounds to try to find the best available refuge areas; by that time, it is too late. 
If refuge areas have not been pre-identified, occupants can easily take cover in areas 
that can become death traps (see Figure 6-57).
When a true shelter is desired for a school that does not have one, retrofitting a 
shelter within the school can be very expensive. An economical alternative is an 
addition to the existing school that can function as a shelter as well as serve another 
purpose. This approach works well for smaller schools, but, for a very large school, 
construction of two or more shelter additions should be considered in order to 
reduce the time it takes to reach the shelter (often there is ample warning time, but 
sometimes an approaching tornado is not noticed until a couple of minutes before it 
strikes).

The recommendations given in Section 6.16 are summarized in Table 6-3 .





 
6.17 REMEDIAL WORK ON EXISTING SCHOOLS

Section 6.6.1 discussed prioritizing and Section 6.6.2 discussed cost. Following up on 
those discussions, many existing schools need building envelope component 
strengthening or structural strengthening. The need for this work is due either to 
deterioration over time and/or inadequate facility strength at the time the school was 
built.
  
It is prudent for school districts to have their existing facilities evaluated. This also 
applies to recently constructed schools that are located in an area where the basic 
wind speed is greater than 90 mph (peak gust), and those schools that will be used for 
emergency response after a storm and schools that will be used for a hurricane 
shelter.
For new schools, areas of concern would typically be the building envelope and 
exterior-mounted mechanical, electrical, and communications equipment. By 
identifying weaknesses and prioritizing and executing the work, many failures can be 
averted. A proactive approach can save significant sums of money and decrease the 
number of instances when schools are impaired or immobilized after a storm.  
For roofs with weak metal edge flashing or coping attachment, face-attachment of 
the edge flashing/coping (as shown in Figure 6-39) is a cost-effective approach to 
greatly improve wind-resistance of the roof system. Fastening rooftop equipment to 
curbs is a cost-effective approach to avoid the type of problems shown in Figure 6-19.
During planned roof covering replacement, by tearing off the existing roof covering 
rather than re-covering, there is the opportunity to evaluate the structural integrity of 
the deck and deck attachment and upgrade its attachment if necessary. Many older 
decks are poorly attached (Figure 6-58); hence, if their attachment is not upgraded, 
blow-off of the deck and the new roof covering could occur. The two deck panels 
shown in Figure 6-58 blew away because their attachment to the roof structure was 
inadequate. An SPF roof covering was over the deck panels that blew away because of 
the characteristics of this type of covering, membrane propagation failure did not 
occur, as would have been the case with built-up, modified bitumen, or single-ply roof 
membranes. Cementitious wood-fiber decks were commonly used on schools built in 
the 1950s and 1960s. Decks constructed during that era typically had very limited 
uplift resistance due to weak connections to the support structure. 
Design guidance pertaining to existing decks is presented in "Uplift Resistance of 
Existing Roof Decks:  Recommendations for Enhanced Attachment During Reroofing Work," RCI 
Interface, Thomas L. Smith, January 2003, pp. 14.
Weak non-load bearing masonry walls, poorly connected precast concrete panels, 
long-span structures (e.g., at gyms) with limited uplift resistance, and weak glass 
curtain walls are common problems with many older schools. Although the technical 
solutions to these problems are not difficult, the cost of the remedial work is 
normally quite expensive. If remediation funds are not available, it is important to 
minimize the risk of injury and death by evacuating areas that have this type of 
construction when winds above 60 mph are forecast. 
For schools located in wind-borne debris regions, if the exterior glazing is not 
missile-resistant, equipping the openings with shutters is a cost-effective approach to 
provide protection.

The recommendations given in Section 6.17 are summarized in Table 6-4.





6.18 REFERENCES AND SOURCES OF ADDITIONAL INFORMATION 

American Institute of Architects, Buildings at Risk: Wind Design Basics for Practicing 
Architects, 1997.
 
Federal Emergency Management Agency, Building Performance: Hurricane Andrew in 
Florida, FEMA FIA-22, Washington, DC, December 1992.

Federal Emergency Management Agency, Building Performance: Hurricane Iniki in 
Hawaii, FEMA FIA-23, Washington, DC, January 1993.

Federal Emergency Management Agency, Corrosion Protection for Metal Connectors in 
Coastal Areas, FEMA Technical Bulletin 8-96, Washington, DC, August 1996.

Federal Emergency Management Agency, Typhoon Paka: Observations and 
Recommendations on Building Performance and Electrical Power Distribution System, Guam, 
U.S.A., FEMA-1193-DR-GU, Washington, DC, March 1998.

Federal Emergency Management Agency, Hurricane Georges in Puerto Rico, FEMA 339, 
Washington, DC, March 1999.

Federal Emergency Management Agency, Oklahoma and Kansas Midwest Tornadoes of 
May 3, 1999, FEMA 342, Washington, DC, October 1999.

Federal Emergency Management Agency, Coastal Construction Manual, Third Edition, 
FEMA 55, Washington, DC, 2000.

Federal Emergency Management Agency, Design and Construction Guidance for 
Community Shelters, FEMA 361, Washington, DC, July 2000.

Federal Emergency Management Agency, Primer to Design Safe School Projects in Case of 
Terrorist Attacks, FEMA 428, Washington, DC, October 2003.

Federal Emergency Management Agency, Tornado Protection, Selecting Safe Areas in 
Buildings, FEMA 431, Washington, DC, October 2003.

National Research Council of Canada, Institute for Research in Construction, Wind 
Design Guide for Mechanically Attached Flexible Membrane Roofs, B1049, 2004.

Rousseau, M.Z., Facts and Fictions of Rain-Screen Walls, Construction Canada, 1990, pp. 40.
Smith, Thomas L., "Insights on Metal Roof Performance in High-wind Regions,"  
Professional Roofing, February 1995, pp. 12 (available on-line at www.nrca.net).

Smith, Thomas L., "Integrating a Lightning Protection System in a Roof System," 
12th International Roofing and Waterproofing Conference Proceedings (CD), 
National Roofing Contractors Association, 2002.

Smith, Thomas L., "Honing in on hangars,"  Professional Roofing, October 2002, pp. 32 
(available on-line at www.nrca.net).

Smith, Thomas L., "Uplift Resistance of Existing Roof Decks:  Recommendations for 
Enhanced Attachment During Reroofing Work," RCI Interface, January 2003, pp. 14.
Smith, Thomas L., "Detailing ASCE 7's changes," Professional Roofing, July 2003, pp. 26 
(available on-line at www.nrca.net).





6.19 GLOSSARY OF WIND TERMS

Basic wind speed. A 3-second gust speed at 33 feet above the ground in Exposure C.   
(Exposure C is flat open terrain with scattered obstructions having heights generally 
less than 30 feet.) Note: Since 1995, ASCE 7 has used a 3-second peak gust measuring 
time.  A 3-second peak gust is the maximum instantaneous speed with a duration of 
approximately 3 seconds. A 3-second peak gust speed could be associated with a given 
windstorm (e.g., a particular storm could have a 40-mile per hour peak gust speed), or 
a 3-second peak gust speed could be associated with a design-level event (e.g., the 
basic wind speed prescribed in ASCE 7).

Building, enclosed. A building that does not comply with the requirements for open or 
partially enclosed buildings.

Building, open. A building having each wall at least 80 percent open. This condition 
is expressed by an equation in ASCE 7.

Building, partially enclosed. A building that complies with both of the following 
conditions:
1. The total area of openings in a wall that receives positive external pressure exceeds 
the sum of the areas of openings in the balance of the building envelope (walls 
and roof) by more than 10 percent, and   
2. The total area of openings in a wall that receives positive external pressure exceeds 
4 square feet or 1 percent of the area of that wall, whichever is smaller, and the 
percentage of openings in the balance of the building envelope does not exceed 
20 percent.
These conditions are expressed by equations in ASCE 7.

Building, regular shaped. A building having no unusual geometrical irregularity in 
spatial form.
Building, simple diaphragm. An enclosed or partially enclosed building in which wind 
loads are transmitted through floor and roof diaphragms to the vertical main wind-
force resisting system.

Components and cladding. Elements of the building envelope that do not qualify as 
part of the main wind-force resisting system.
Escarpment. Also known as a scarp, with respect to topographic effects, a cliff or steep 
slope generally separating two levels or gently sloping areas. 

Exposure. The characteristics of the ground roughness and surface irregularities in 
the vicinity of a building. ASCE 7 defines three exposure categories - Exposures B, C, 
and D. 

Glazing. Glass or transparent or translucent plastic sheet used in windows, doors, and 
skylights.

Glazing, impact-resistant. Glazing that has been shown by an approved test method to 
withstand the impact of wind-borne missiles likely to be generated in wind-borne 
debris regions during design winds.
Hill. With respect to topographic effects, a land surface characterized by strong relief 
in any horizontal direction.

Hurricane-prone regions. Areas vulnerable to hurricanes; in the U.S. and its territories 
defined as:
1. The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is 
greater than 90 miles per hour, and
2. Hawaii, Puerto Rico, Guam, U.S. Virgin Islands, and American Samoa.

Impact-resistant covering. A covering designed to protect glazing, which has been 
shown by an approved test method to withstand the impact of wind-borne missiles 
likely to be generated in wind-borne debris regions during design winds.
Importance factor, I. A factor that accounts for the degree of hazard to human life 
and damage to property. The importance factor adjusts the mean recurrence interval.  
Importance factors are given in ASCE 7.

Main wind-force resisting system. An assemblage of structural elements assigned to 
provide support and stability for the overall structure. The system generally receives 
wind loading from more than one surface.

Mean roof height, h. The average of the roof eave height and the height to the highest 
point on the roof surface, except that, for roof angles of less than or equal to 10 
degrees, the mean roof height shall be the roof eave height.

Missiles. Debris that became or could become ingested into the wind stream.  

Openings. Apertures or holes in the building envelope that allow air to flow through 
the building envelope and that are designed as "open" during design winds. A door 
that is intended to be in the closed position during a windstorm would not be 
considered an opening. Glazed openings are also not typically considered an 
opening. However, if the building is located in a wind-borne debris region and the 
glazing is not impact-resistant or protected with an impact-resistant covering, the 
glazing is considered an opening.

Ridge. With respect to topographic effects, an elongated crest of a hill characterized 
by strong relief in two directions.

Wind-borne debris regions. Areas within hurricane-prone regions located:
1. Within 1 mile of the coastal mean high water line where the basic wind speed is 
equal to or greater than 110 mph and in Hawaii; or
2.  In areas where the basic wind speed is equal to or greater than 120 mph