Hurricane Opal in Florida
A Building Performance Assessment
Federal Emergency Management Agency 
Mitigation Directorate 
FEMA 281/August 30, 1996


The Building Performance Assessment Team Process

In response to hurricanes, floods, earthquakes, and other disasters, the Federal 
Emergency Management Agency (FEMA) often deploys Building Performance Assessment 
Teams (BPATs) to conduct field investigations at disaster sites. The members of 
a BPAT include representatives of public sector and private sector entities who 
are experts in specific technical fields such as structural and civil 
engineering, building design and construction, and building code development and 
enforcement. BPATs inspect disaster-induced damages incurred by residential and 
commercial buildings and other manmade structures; evaluate local design 
practices, construction methods and materials, building codes, and building 
inspection and code enforcement processes; and make recommendations regarding 
design, construction, and code issues. With the goal of reducing the damage 
caused by future disasters, the BPAT process is an important part of FEMA’s 
hazard mitigation activities.

About the Cover

This photograph was taken along the gulf coast in the City of Pensacola Beach, 
Florida, after the passage of Hurricane Opal. In the foreground are the remains 
of a structure built before the city adopted the floodplain management ordinance 
required for participation in the National Flood Insurance Program (NFIP).The 
structure in the background was built after the adoption of the required 
ordinance and was therefore required to meet NFIP standards for construction in 
the Coastal High Hazard Area. The dramatic difference between the post-storm 
conditions of these two structures underscores the importance of proper 
construction in coastal areas subject to hurricanes.




TABLE OF CONTENTS

EXECUTIVE SUMMARY 1

1 INTRODUCTION 1-1
1.1 Purpose 1-1
1.2 Background 1-1
1.3 Hurricane Opal — Storm Conditions 1-3
1.4 Local, State, and Federal Siting and Building Code Requirements 1-3

2 SITE OBSERVATIONS 2-1
2.1 Typical Pre-FIRM and Post-FIRM Construction 2-1 
2.2 Observations of Wind Damage 2-1
2.3 Observations of Flood Damage 2-1
2.3.1 Erosion and Scour 2-3
2.3.2 Debris 2-3
2.3.3 Slab Foundations 2-3
2.3.4 Pile and Pier Foundations 2-6
2.3.5 Framing Systems 2-6
2.3.6 Connections 2-7
2.3.7 Bracing 2-7
2.3.8 Breakaway Construction and Enclosures 2-9
2.3.9 Stairs, Decks, and Porches 2-9
2.3.10 Utilities 2-9
2.3.11 Seawalls 2-12
2.3.12 Drainage and Drainage Structures 2-13
2.4 Incorporation of Pre-FIRM Construction into New Construction 2-13
2.5 Design, Construction, and Workmanship 2-13

3 RECOMMENDATIONS 3-1
3.1 Application of V-Zone and A-Zone Design and Construction Requirements 3-1
 3.1.1 FEMA to Issue Revised FIRMs 3-1
 3.1.2 Communities Using Higher Standards in Coastal A-Zones 3-1
3.2 Permitting, Plan Review, and Inspection 3-3
3.3 Construction Materials 3-3
3.4 Repair and Retrofit of Damaged Structures 3-4
3.5 New Construction and Substantial Improvements 3-4
3.5.1 Pile, Post, Column, and Pier Foundations 3-4
3.5.2 Slabs and Grade Beams 3-5
3.5.3 Framing Systems 3-12
3.5.4 Connections 3-12
3.5.5 Bracing 3-12
3.5.6 Breakaway Construction, Free-Of-Obstruction, and Enclosure Requirements 
Under the NFIP 3-12
3.5.7 Stairs, Decks, and Porches 3-13
3.5.8 Utilities 3-13
3.5.9 Seawalls and Erosion Control Structures 3-13

4 REFERENCES 4-1

APPENDIX — Building Performance Assessment Team Members

Figures

Figure 1-1 Florida counties included in the Hurricane Opal Federal disaster 
declaration. 1-2

Figure 2-1 Debris washed inland as a result of surge action from Hurricane Opal 
(note circled boats). 2-2

Figure 2-2 Beach erosion caused major damage to structures, as well as roads and 
utilities. 2-2

Figure 2-3 Beach erosion eliminated protection for structures. It is important 
that the beach and dunes be rebuilt as soon as possible. 2-4

Figure 2-4 Erosion such as this took place along the gulf coast, causing 
structures to be undermined and resulting in damage. 2-4

Figure 2-5 Debris, consisting of broken concrete and wood framing systems, 
generated by surge action. 2-5

Figure 2-6 Undermining of concrete decks and floor slabs caused the failure of 
many unreinforced concrete structures. 2-5

Figure 2-7 These piles were not embedded deep enough to survive the erosion of 
the sand. 2-6

Figure 2-8 These piles were not long enough and were spliced to add depth. 2-7

Figure 2-9 The floor beam connection and beam support shown here illustrate the 
lack of design and proper construction observed on many damaged structures. 2-8

Figure 2-10 This undamaged threaded rod & turnbuckle cross-bracing continues to 
provide support as designed. 2-8

Figure 2-11 These breakaway walls functioned as designed, lessening the 
pressures of water, sand, and debris on the structure. 2-10

Figure 2-12 Utility lines and boxes dislocated by hurricane forces. 2-10

Figure 2-13 Interior view of breakaway wall blocked by air conditioning unit and 
platform (see Figure 2-11). 2-11

Figure 2-14 These breakaway walls functioned as designed. Note the loss of the 
air conditioning unit platform. 2-11

Figure 2-15 Fractured seawall, damaged by storm forces. 2-12

Figure 3-1 This well-constructed concrete structure survived the storm with 
little or no damage, even with 5 feet of erosion. 3-5

Figure 3-2 Posts are placed in excavated holes and may be anchored in a concrete 
pad at the bottom of the hole. 3-6

Figure 3-3 Posts can also be anchored in concrete encasements. 3-7

Figure 3-4 Post on concrete bearing pad. 3-8

Figure 3-5 Post on earth bearing. 3-8

Figure 3-6 Anchorage of post. 3-9

Figure 3-7 Piles are mechanically driven into the ground and are therefore less 
susceptible to high-velocity flooding, erosion, conical scour, and pullout. 3-10

Figure 3-8 The depth of pile embedment provides stability by enabling the pile 
to resist lateral and vertical loads through passive earth pressure. 3-11

Figure 3-9 Post/pile foundation. 3-11

Figure 3-10 Wood stud breakaway wall (after FEMA 1986). 3-14

Figure 3-11 Light-gauge metal stud breakaway wall (after FEMA 1986). 3-15

Figure 3-12 Installation of cantilevered floor joists as a retrofit for an 
elevated home to allow for a mechanical balcony. 3-16

Figure 3-13 Installation of a mechanical balcony as a retrofit for an elevated 
home. 3-16





EXECUTIVE SUMMARY

On October 4, 1995, Hurricane Opal made landfall on Santa Rosa Island, Florida, 
near Navarre Beach, at approximately 6:00 p.m. c.d.t. (central daylight time.) 
As a result of the damage caused by Hurricane Opal, President Clinton declared 
15 counties in the Florida Panhandle and Lee County, on the southwest Florida 
coast, Federal disaster areas (see Figure 1-1).  

The Federal Emergency Management Agency (FEMA) deployed a Building Performance 
Assessment Team (BPAT) whose mission was to evaluate structural damage and 
recommend mitigation measures that will enhance the performance of buildings in 
future storms. The team was composed of engineers and building construction 
specialists from FEMA, the State of Florida, and the private sector (see the 
Appendix for a list of the team members). The BPAT conducted its evaluation in 
the area where most of the severe damage was concentrated: along a 200-mile 
stretch of Florida’s Gulf of Mexico shoreline, between Pensacola Beach, in 
Escambia County, and St. Joseph Spit, in Gulf County (see Figure 1-1). The 
BPAT’s observations focused on the performance of buildings during the 
hurricane, including both successes and failures. These observations and the 
BPAT’s recommendations are documented in this report.

Preliminary estimates by the insurance industry indicate that Opal may be one of 
the most costly natural disasters to affect the United States (ranking only 
behind Hurricane Andrew; the Northridge, California, earthquake; and Hurricane 
Hugo).  According to State of Florida estimates, more structures were damaged or 
destroyed by the effects of flooding and erosion during Hurricane Opal than in 
all other coastal storms affecting Florida in the past 20 years combined.  

Most of the structural damage associated with the storm appeared to have been 
caused by coastal flood forces — storm surge, wind-generated waves, flood-
induced erosion, and floodborne debris. Wind damage along the coast was confined 
primarily to roof damage, sign damage, tree damage, and similar impacts and was 
judged by the BPAT to be less severe and less extensive than flood damage.  

Construction along and near the shoreline in the study area was generally 
governed by one or more of the following:

- The Standard Building Code, enforced by local or county governments

- National Flood Insurance Program (NFIP) construction requirements — in 
identified Special Flood Hazard Areas — enforced by local or county governments

- State construction requirements for structures seaward of the Coastal 
Construction Control Line, enforced by the Florida Department of Environmental 
Protection

To participate in the NFIP, a community must adopt and enforce a floodplain 
management ordinance based on the Flood Insurance Rate Map (FIRM) issued for the 
community by FEMA. The communities in the study area include structures built 
before the adoption of the floodplain management ordinance and structures built 
after the adoption of the ordinance. The former are referred to as “pre-FIRM” 
structures, the later as “post-FIRM.” Typical pre-FIRM structures in the study 
area are one-story concrete block or wood-frame structures built on slab-on-
grade foundations, one- to three-story concrete block structures, and one- to 
three-story wood-frame structures founded on timber piles. Many of these 
structures were behind concrete sheetpile seawalls. Typical post-FIRM structures 
in the study area are one-, two-, and three-story wood-frame structures elevated 
on timber or concrete pile foundations. Post-FIRM structures, although 
sustaining damage, performed much better than the pre-FIRM structures. 

Flood Damage and Vulnerable Components

Because most of the structural damage observed by the BPAT along the Gulf of 
Mexico shoreline appeared to have been caused by flood forces rather than wind 
forces, the team focused on flood-induced damage. The observations of the team 
presented in this report address following issues:

- storm-induced erosion and scour
- debris flow and impact
- slab foundations
- pile and pier foundations
- framing systems
- connections
- bracing
- breakaway construction and enclosures below elevated buildings
- stairs, decks, and porches
- utilities
- seawalls
- drainage and drainage structures

Other issues discussed in this report include (1) the incorporation of pre-FIRM 
construction into new construction during the improvement of existing structures 
and (2) structures that appear to have been built without the aid of detailed 
plans prepared by a design professional. The BPAT found that poor workmanship 
frequently accompanied the lack of professional design in such instances.

Recommendations

The BPAT developed recommendations that address observed damages and 
vulnerabilities for both new construction and substantial improvements to 
existing structures in areas subject to coastal and hurricane storm forces. 
These recommendations include the following:

- Restudies and FIRM revisions now underway for the affected communities will 
use updated V-Zone mapping procedures and may result in more extensive areas 
being shown as V-Zones. Consequently, until such time as revised FIRMs are 
completed, the affected communities should consider studying local coastal 
flooding conditions that occurred during Hurricane Opal to determine whether 
areas shown as coastal A-Zones on the current FIRMs, as well as areas within 
several hundred feet of the Gulf of Mexico shoreline, are actually subject to V-
Zone flood forces. If such areas are identified, the affected communities should 
strongly encourage the owners of new construction and substantial improvements 
to existing structures within those areas to conform with V-Zone construction 
standards. In addition, if areas shown as A-Zones on the current FIRMs are 
determined to be subject to V-Zone forces, the BFEs shown for those areas are 
likely to increase. Therefore, communities should also strongly encourage the 
owners of new construction and substantial improvements to existing structures 
in such areas to construct the lowest floors of their structures several feet 
above the BFEs shown on the current FIRMs.

- For all areas known to be subject to high-velocity wave action, strong 
currents, erosion, or combinations thereof — regardless of flood zone 
designation — the embedment depths specified for pile foundations should be 
sufficient to ensure that the foundation will withstand anticipated erosion and 
storm forces. Foundations for masonry columns should be designed to withstand 
all anticipated flood, erosion, debris, and wind forces. Shallow footings should 
not be used to support masonry columns where the risk of undermining exists.

- In areas subject to storm-induced erosion, regardless of the flood zone 
designation, any slabs serving as floors for habitable spaces should be designed 
and constructed as structural slabs, to withstand all anticipated erosion, 
scour, and storm forces, and attached to sufficient foundation systems that do 
not rely on underlying soil for support.

- In areas subject to storm-induced erosion, regardless of the flood zone 
designation, slabs used solely for parking should not be attached to structural 
members and should be designed and constructed to break into small pieces in the 
event of undermining, thereby minimizing potential transfer of flood loads to 
the structure.

- All materials should meet or exceed the minimum requirements for building 
materials in the Standard Building Code and FEMA’s Technical Bulletin 2-93, 
Flood-Resistant Materials Requirements for Buildings Located in Special Flood 
Hazard Areas (FEMA 1993b).

- Repairs of damaged structures should be completed in accordance with 
applicable Federal, State, and local codes and regulations and should be 
inspected to ensure conformance with building codes and floodplain management 
requirements.

- Engineered plans signed and sealed by a registered design professional should 
be provided for both new construction and substantial improvements to existing 
structures in areas subject to coastal storm forces. Siting and construction in 
100-year coastal flood hazard areas must meet (and, if possible, exceed) setback 
and elevation requirements.

This report includes photographs taken by the BPAT during the site visit. Also 
included are engineering design drawings that provide details which can be used 
to enhance building performance under hurricane and coastal flood conditions.





1 INTRODUCTION

1.1 Purpose

This report presents the findings of the Building Performance Assessment Team 
(BPAT) regarding building successes and failures during Hurricane Opal and 
recommends mitigation measures that will enhance the performance of buildings in 
future storms. The Appendix lists the BPAT members.

Typical construction types are defined for structures built prior to and after 
the affected communities’ adoption of the floodplain management ordinance 
required for participation in the National Flood Insurance Program (NFIP). 
Because the ordinance is based on flood hazard information shown on the Flood 
Insurance Rate Map (FIRM) issued for each community, these structures are 
referred to as “pre-FIRM” and “post-FIRM,” respectively. The BPAT’s observations 
regarding flood and wind damage caused by the storm are described in detail, and 
recommendations are presented regarding design and construction of new 
structures and substantial improvements to existing structures; permitting, plan 
review, and inspection; construction materials; and repair and retrofit of 
damaged structures.

1.2 Background

Hurricane Opal made landfall on Santa Rosa Island, in Santa Rosa County, 
Florida, near Navarre Beach, at approximately 6:00 p.m. c.d.t. (central daylight 
time) on Wednesday, October 4, 1995. Fifteen counties in the Florida Panhandle 
were declared Federal disaster areas (see Figure 1-1). Most of the damage was 
concentrated in six counties: Escambia, Santa Rosa, Okaloosa, Walton, Bay, and 
Gulf. Lee County, along the gulf coast in southwest Florida, was declared a 
Federal disaster area because of rainfall-induced flooding associated with the 
same storm system.

The most severe damage caused by Opal was concentrated along a 200-mile stretch 
of Florida’s Gulf of Mexico shoreline, between Pensacola Beach (Escambia County) 
and St. Joseph Spit (Gulf County). This is the area where the BPAT conducted its 
field inspections (see Figure 1-1). The results of these inspections and the 
BPAT’s review of post-storm video taken by the Florida Department of 
Environmental Protection (FDEP), Bureau of Beaches and Coastal Systems, led to 
the conclusion that most of the structural damage associated with the storm was 
caused by coastal flood forces — storm surge, wind-generated waves, storm-
induced erosion, and floodborne debris. Flood damage also occurred along the 
shorelines of Santa Rosa Sound, Choctawhatchee Bay, and other inland waters.

[Begin figure]
Figure 1. is a map showing Florida counties included in the Hurricane Opal 
Federal disaster declaration.
[End figure]

Wind damage along the coast was confined largely to roof damage, sign damage, 
tree damage, and similar impacts and was judged by the BPAT to be less severe 
and less extensive than the flood damage. However, wind damage extended 
throughout the affected counties. Newspaper accounts indicated that 
approximately 18,000 dwelling units (e.g., homes, apartments, hotel/motel units) 
in 10 panhandle counties were rendered uninhabitable by Hurricane Opal and 
approximately one-fifth of these units were destroyed (Panama City News Herald 
1995). The BPAT was unable to confirm these estimates.

Data from the FDEP (1995) indicate that approximately 990 coastal structures 
along the Gulf of Mexico shoreline incurred 50 percent or more damage (i.e., 
substantial damage). This total includes over 500 single-family dwellings and 
over 300 multi-family structures (containing 1,000 dwelling units and 800 
motel/hotel units). The FDEP data also show that over 3 miles of concrete and 
timber bulkheads and retaining walls were damaged or destroyed. According to 
State of Florida estimates, more structures were damaged or destroyed by the 
effects of flooding and erosion during Hurricane Opal than in all other coastal 
storms affecting Florida in the past 20 years combined.

Preliminary estimates from the insurance industry show total insured losses from 
wind damage from the storm to be approximately $2 billion, making Opal one of 
the most costly natural disasters to affect the United States (ranking only 
behind Hurricane Andrew; the Northridge, California, earthquake; and Hurricane 
Hugo).

1.3 Hurricane Opal — Storm Conditions

Hurricane Opal was classified as a Category 3 storm on the Saffir-Simpson scale 
at the time of landfall, with a central pressure of 940 millibars (mb) and 
recorded sustained wind speeds of approximately 110 to 115 miles per hour (mph). 
Recorded wind speeds rapidly decayed to 86 to 92 mph just inland. The storm was 
moving north-northeast with a forward speed of 22 mph at landfall (National 
Oceanic and Atmospheric Administration 1995).

Water level data from a National Oceanic and Atmospheric Administration (NOAA) 
tide gage on the Panama City Beach pier show a peak water level of approximately 
8.5 feet above Mean Lower Low Water (MLLW) at 6:00 p.m. c.d.t., nearly 8 feet 
above the predicted astronomical tide. Water level data from the NOAA gage at 
Apalachicola show a peak water level of approximately 6.6 feet MLLW at 7:30 p.m. 
c.d.t., approximately 6 feet above the predicted astronomical tide.

High-water mark surveys conducted after Hurricane Opal (Michael Baker, Jr. 1995) 
show that water levels ranged from approximately 8 to 11 feet National Geodetic 
Vertical Datum (NGVD) along Santa Rosa Island between Pensacola Beach and Fort 
Walton Beach, approximately 12 to 20 feet NGVD between Destin and Seagrove 
Beach, and approximately 8 to 12 feet NGVD along Panama City Beach.

1.4 Local, State, and Federal Siting and Building Code Requirements

Construction along and near the shoreline in the study area was generally 
governed by one or more of the following:  the Standard Building Code, enforced 
by local or county governments; NFIP construction requirements — in identified 
Special Flood Hazard Areas — enforced by local or county governments; and State 
construction requirements for structures seaward of the Coastal Construction 
Control Line (CCCL), enforced by FDEP, Bureau of Beaches and Coastal Systems 
(formerly known as the Florida Department of Natural Resources, Division of 
Beaches and Shores).

FIRMs which show Base Flood Elevations (BFEs) that include wave height effects 
were adopted by communities in the study area between June 1983 and August 1987. 
(The base flood, also referred to as the 100-year flood, is the flood that has a 
1-percent probability of being equaled or exceeded in any given year and is the 
basis for the regulatory requirements of the NFIP.) Because the NFIP Flood 
Insurance Studies on which the FIRMs are based were completed at different 
times, during which V-Zone mapping criteria were evolving, some of the studies 
accounted for wave setup, wave runup, and erosion, and others did not.

The Flood Insurance Studies indicate that the predicted 100-year stillwater (or 
storm surge) elevations along the majority of the Gulf of Mexico shoreline in 
the study area range from 4 feet to 6 feet NGVD. In the same area, V-Zones 
generally range from 100 to 300 feet in width and the wave crest elevations in 
the V-Zone range from 7 to 9 feet NGVD. Higher elevations are indicated for the 
Pensacola Beach and Perdido Key areas, where the predicted 100-year stillwater 
elevations range from 8 feet to 12 feet NGVD, V-Zones range from 200 to 400 feet 
in width, and V-Zone wave crest elevations range from 12 to 15 feet NGVD.

The State of Florida established the CCCL along Florida’s sandy beach shorelines 
to delineate those areas subject to erosion or other adverse impacts during a 
100-year storm. Specific elevation and construction requirements are enforced by 
the State seaward of the CCCL. With the exception of Bay County, the portions of 
the CCCL in the study area were adopted by the State between 1982 and 1991 and 
reflect anticipated 100-year storm impact zones. However, the pre-Opal CCCL in 
Bay County was essentially unchanged from a 50-foot setback line established by 
the State in 1975 and did not include all areas subject to 100-year storm 
impacts. After Hurricane Opal, the State adopted a revised CCCL for Bay County 
on an emergency basis. The new line is 100 feet landward of the pre-Opal line 
and became effective on October 16, 1995. Reconstruction of many damaged or 
destroyed structures along the Bay County shoreline will now be subject to CCCL 
construction requirements.

The FDEP has also completed its own studies that predict 100-year stillwater 
elevations along the Gulf of Mexico shoreline.  FDEP studies for the reach 
between Escambia and Bay Counties generally show 100-year stillwater elevations 
ranging between 11 feet and 12 feet NGVD. The 5-foot to 6-foot difference 
between FDEP and NFIP 100-year stillwater levels is attributed to the inclusion 
of dynamic wave setup by FDEP.

A comparison of V-Zone boundaries and the location of the State’s CCCL had not 
been completed at the time this report was prepared (a comparison is expected by 
late 1996). However, the State’s foundation and elevation requirements seaward 
of the CCCL (i.e., pile penetration requirements and lowest floor elevations) 
are known to be more stringent than NFIP V-Zone requirements. Likewise, the 
State’s wind load requirements seaward of the CCCL are known to be more 
stringent than the wind load requirements of the Standard Building Code. 
According to the FDEP (1995), no major habitable structures located seaward of 
the CCCL and permitted by the State under current standards sustained 
significant structural damage during Hurricane Opal. In contrast, the FDEP 
reported that over one-half of the pre-existing major habitable structures 
seaward of the CCCL (i.e., structures either not permitted by the State or 
constructed prior to State permitting requirements) sustained structural damage 
during the storm.





2 SITE OBSERVATIONS

2.1 Typical Pre-FIRM and Post-FIRM Construction

Typical pre-FIRM structures in the study area are one-story concrete block or 
wood-frame structures built on slab-on-grade foundations, one- to three-story 
concrete block structures, and one- to three-story wood-frame structures founded 
on timber piles. Many of these structures are behind concrete sheetpile 
seawalls. Many pre-FIRM structures were substantially damaged by the surge 
accompanying the storm event and were often destroyed because of foundation 
collapse, wave attack, or both.

Typical post-FIRM structures in the study area are one-, two-, and three-story 
wood-frame structures elevated on timber or concrete pile foundations. Some of 
these are new structures that either incorporate older, pre-FIRM structures or 
were built over them. Post-FIRM elevated structures sustained some wind and 
flood damage but, overall, performed much better than pre-FIRM structures that 
were at-grade or that were elevated but not to the BFE or CCCL requirements.

2.2 Observations of Wind Damage

Wind damage observed by the BPAT was generally confined to roofing shingles and 
tiles, exterior sheathing, unsecured air conditioning compressors, power poles 
and lines, and signs. However, the wind damage observed did not constitute a 
large portion of the total damage to structures.

2.3 Observations of Flood Damage

Flood damage was observed along the Gulf of Mexico shoreline at all sites 
visited by the BPAT (see Figures 2-1 and 2-2). Structures damaged by flood 
forces generally fell into the following categories:

- pre-FIRM structures founded on slabs or shallow footings and located in mapped 
V-Zones

- post-FIRM structures in mapped A-Zones, B-Zones, C-Zones, and X-Zones founded 
on slabs or shallow footings, but exposed to high-velocity flows, high-velocity 
wave action, flood-induced erosion, floodborne debris, or burial by overwash

- post-FIRM elevated structures not properly constructed or not elevated to or 
above the elevation reached by storm surge and wave effects

- pre- and post-FIRM structures dependent, in part or completely, on failed 
seawalls or bulkheads for protection and foundation support.

[Begin figures]
Figure 2-1 is a photo showing debris washed inland as a result of surge action 
from Hurricane Opal.

Figure 2-2 is a photo showing how beach erosion caused major damage to 
structures, as well as roads and utilities.
[End figures]

2.3.1 Erosion and Scour

Where sand dunes existed before Hurricane Opal, significant loss of dune height 
and width was observed. Many dunes were breached or flattened (see Figure 2-3). 
Those that remained after the storm were scarped and weakened. Duneface retreat 
of 75 feet to 100 feet was observed in several locations. Overwash of eroded 
dune sediments was common, sometimes extending over 500 feet inland and causing 
burial of roads and at-grade construction by 1 to 4 feet of sand.

[Begin figure]
Figure 2-3 is a photo showing how beach erosion eliminated protection for 
structures. It is important that the beach and dunes be rebuilt as soon as 
possible. Arrows point to walkways used to traverse dune that has been washed 
away.
[End figure]

In some cases, an estimated 10 to 20 feet of vertical relief was lost at the 
seaward edge of high dune and bluff areas. Many structures atop high dunes or 
bluffs collapsed because of a loss of support, either from the undermining of 
slab foundations or from inadequate pile embedment (see Figure 2-4).

[Begin figure]
Figure 2-4 is a photo showing how erosion such as this took place along the gulf 
coast, causing structures to be undermined and resulting in damage.
[End figure]

Ground levels at many front-row elevated structures that survived Hurricane Opal 
were typically reduced 3 to 7 feet, or more. In addition, local scour 
depressions were observed at the bases of many piles, indicating that 6 to 12 
inches of additional soil was lost immediately adjacent to the piles. Scour 
during the storm probably rendered greater than 6 to 12 inches of soil around 
the piles unsupporting.

Large scour depressions were observed where large volumes of water flowed during 
the storm. Depressions measuring 10 to 40 feet in length and width and 2 to 4 
feet in depth were observed around some pile-supported structures and near the 
corners of some at-grade construction. Structures that seemed particularly 
vulnerable included the following:

- structures at the landward termination of roads and driveways that funneled 
floodwaters toward the structures

- structures between drainage basins or lakes and larger bodies of water

- structures near locations where floodwaters crossed or breached the barrier 
islands

2.3.2 Debris

Small debris was widespread, ranging from household items to construction 
materials. These items did not cause structural damage to buildings, 
foundations, or other building components. Evidence of much larger debris 
shifted by floodwaters was also observed, including pier piles and braces, 
concrete slabs, dumpsters, automobiles, boats, and collapsed houses (see Figure 
2-5). Many of these objects washed into buildings, and some caused structural 
damage.

[Begin figure]
Figure 2-5 is a photo showing how debris, consisting of broken concrete and wood 
framing systems, was generated by surge action
[End figure]

2.3.3 Slab Foundations

Many slab failures were noted in all types of structures (see Figure 2-6). The 
major reason for these failures was the loss of support coupled with a lack of 
reinforcing in the slabs. Welded reinforcing wire fabric was observed in many 
slabs but did not prevent failure of the slabs once they were undermined.

[Begin figure]
Figure 2-6 is a photo showing how undermining of concrete decks and floor slabs 
caused the failure of many unreinforced concrete structures
[End figure]

2.3.4 Pile and Pier Foundations

Three to seven feet of vertical erosion at the seaward row of piles was common 
(see Figure 2-7). This erosion, coupled with insufficient penetration of the 
piles on many structures, led to structural damage to or collapse of primarily 
pre-FIRM structures. Undersized piles (6-inch diameter timber in some instances) 
were not sufficient to resist storm forces; they generally failed and resulted 
in structural damage or collapse. Piers constructed of concrete blocks on 
shallow footings frequently collapsed as a result of erosion. Well-designed and 
well-constructed pile and pier foundations withstood the forces exerted by the 
storm. Use of splicing techniques was also observed on some eroded piles (see 
Figure 2-8). Although the splicing of piles placed these structures at increased 
risk of failure, no failures related to spliced piles were observed.

[Begin figures]
Figure 2-7 is a photo showing how these piles were not embedded deep enough to 
survive the erosion of the sand. As a result, there is now a large gap between 
the bottoms of the pilings and the ground surface.

Figure 2-8 is a photo showing how these piles were not long enough and were 
spliced to add depth. The splicing was exposed by storm-induced erosion.
[End figures]

2.3.5 Framing Systems

The BPAT found many examples of poor framing of timber floor beams and joists in 
platform-type construction. In particular, poorly fashioned beam-to-beam and 
joist-to-beam connections were common. Typical problems included the following:

- pile notching greater than 50 percent of pile cross-section

- poor alignment of piles, which resulted in unsupported beams at piles

- use of wooden shims to support beams (i.e., to compensate for notches cut too 
low)

- over reliance on nails and thin metal straps/hangers

Glue-laminated beams and joists were observed in exterior applications in some 
recent post-FIRM residential construction. The use of laminated structural 
members in exterior applications is of interest because this practice has not 
been widely observed by previous BPATs. Although laminated structural members 
rated for exterior use are available, the Hurricane Opal BPAT could not 
determine the rating of those it saw. No failures of these beams and joists were 
observed however.

2.3.6 Connections

Many of the connections observed were deficient. The BPAT observed widespread 
corrosion of galvanized straps, hangers, and joist-to-beam ties beneath elevated 
buildings. Some of the corroded connectors had failed either before or during 
the storm.  

The BPAT observed some galvanized strap connectors between piles, beams and 
joists (in otherwise good condition) that failed as a result of insufficient 
nailing or because storm forces exceeded the design forces (see Figure 2-9). 
This was not a common mode of failure, however. The BPAT also found evidence 
that structural components had pulled away from one another when acted on 
simultaneously by flood and wind forces, despite the presence of the galvanized 
connectors. In some instances, foundation piles and beams were well-connected 
and withstood storm forces, while walls or upper structure components were 
poorly connected and were damaged or destroyed by wind forces, flood forces, or 
both.

[Begin figure]
Figure 2-9 is a photo showing how the floor beam connection and beam support 
illustrates the lack of design and proper construction observed on may damaged 
structures. Note the bolt pullouts. Also, the beam support is attached to the 
pile with lag bolts rather than bolts that extend through the pile
[End figure]

2.3.7 Bracing

The use of 2 x 8 or similar timber cross-bracing between timber piles was common 
beneath elevated wood-frame structures. Some bracing failures were observed that 
were apparently due to horizontal loading from water, debris, or both. The use 
of threaded galvanized rods and turnbuckles as cross-bracing was less common 
(see Figure 2-10). No failures of this type of bracing were noted, but debris 
was trapped by the bracing, and in some instances, the rods were bent by lateral 
loads imposed by the force of flood waters acting on the trapped debris.  

[Begin figure]
Figure 2-10 is a photo showing how this undamaged threaded rod and turnbuckle 
cross-bracing continues to provide additional support as designed.
[End figure]

Use of knee bracing was also prevalent in elevated wood-frame structures. A 
common problem observed with knee bracing was that timber piles had been 
notched, some deeply, to accommodate bearing seats for tie-in purposes. Although 
the BPAT did not observe any structural failures that could be definitively 
linked to this problem, notching of piles can undermine their structural 
integrity and should therefore be avoided.

2.3.8 Breakaway Construction and Enclosures

There were a number of damaged or destroyed enclosures below elevated structures 
(see Figure 2-11), many with electrical wiring attached to breakaway walls. The 
presence of breakaway walls indicates the designer was aware of potential flood 
impacts. However, the placement or attachment of utilities to breakaway walls 
below the elevated portions of the structures demonstrates, at a minimum, lack 
of awareness of local, CCCL, and NFIP regulations by owners or contractors, or 
possibly disregard of those regulations. 

In some post-FIRM structures with breakaway walls below the lowest habitable 
floor, the walls broke away as intended but in doing so, damaged exterior 
sheathing and wall finishes above the lowest floor. The damage above the 
breakaway wall was usually minor but could have been prevented by better design 
and construction of this detail (as shown in Figure 2-11). Rolldown garage doors 
were damaged or destroyed in pre-FIRM and post-FIRM construction alike (see 
Figure 2-11).

[Begin figure]
Figure 2-11 is a photo showing how these breakaway walls functioned as designed, 
lessening the pressures of water, sand, and debris on the structure.
[End figure]

2.3.9 Stairs, Decks, and Porches

Timber stairs and decks were frequent casualties of the storm. Many were 
supported by short, small-diameter shallow posts or piles. Some decks were 
supported by knee braces attached to structural piles supporting the main 
structure. Decks of this design seemed to better resist Opal’s forces. Loss of 
decks sometimes led to roof damage where roof overhangs were supported by posts 
attached to the decks. In one instance, a deck located seaward of the State’s 
CCCL and permitted by the State survived the storm, while the landward habitable 
structure (behind the CCCL and not within the State’s jurisdiction) was 
destroyed.

2.3.10 Utilities

The BPAT noted several problems associated with utilities and utility 
connections at habitable structures:

- Placement of electric meters, panels, boxes, and wiring below a building’s 
lowest habitable floor, rendering that equipment vulnerable to storm surge, 
wave, debris and overwash damage (see Figure 2-12).

- Attachment of wiring, conduit, and electrical panels to breakaway walls (see 
Figure 2-13).

- Failure to adequately support and fasten air conditioning compressor units 
(see Figure 2-14). Many support platforms were destroyed, leading to compressor 
damage.  Some platforms survived, while unfastened compressor units were blown 
or washed away. Units not properly supported and attached were also observed to 
have caused damage to exterior walls of some structures.

- Placement of utility lines, septic systems, and mechanical connections and 
equipment, including air conditioning units, on the sides or seaward of 
buildings, rather than landward of the building. Loss of air conditioning units 
and/or utility/mechanical components sometimes led to damage of the main 
structure.

[Begin figures]
Figure 2-12 is a photo showing utility lines and boxes dislocated by hurricane 
forces. Not that the cross-bracing and pile support system remain in good 
condition after the storm.

Figure 2-13 is a photo showing the interior view of breakaway wall blocked by 
air conditioning unit and support platform. Electric cooling lines were extended 
through the breakaway panel.

Figure 2-14 is a photo showing how breakaway panels functioned as designed. Note 
the loss of the air conditioning unit platform.
[End figures]

2.3.11 Seawalls

The BPAT observed widespread failure of seawalls and bulkheads along the Gulf of 
Mexico shoreline (see Figure 2-15). Damage figures from the State of Florida 
revealed that over 3 miles of seawalls and bulkheads were destroyed by Hurricane 
Opal, including 1.3 miles of concrete walls, 1.0 mile of concrete block walls, 
and 0.8 mile of timber walls (FDEP 1995). Failed walls contributed to damage of 
buildings, pools, and other structures, due to loss of backfill and generation 
of debris.

[Begin figure]
Figure 2-15 is a photo showing a fractured seawall, damaged by storm forces, 
Note the erosion of the bank behind the wall.
[End figure]

Many walls appeared to have failed because wing walls or return walls were 
flanked by erosion and scour. Many seawall returns flanked by erosion and scour 
were no more than 20 to 30 feet long, although some longer returns (50 feet to 
75 feet) were also flanked.

Seawalls were usually destroyed when backfill was washed from behind the walls 
because of overtopping, insufficient wall embedment, or return wall flanking.  
Habitable structures founded on slabs or shallow foundations, swimming pools, 
and other structures that relied on seawalls to retain supporting soil, were 
frequently undermined and destroyed when seawalls failed.
The BPAT noted that retaining walls constructed of concrete blocks were 
particularly vulnerable to damage by Hurricane Opal. Walls most likely to have 
survived were observed to have:


- reinforced concrete slab or sheetpile construction

- sufficient wall height or backfill protection to prevent significant 
overtopping and loss of backfill

- sufficient anchorage and embedment to prevent collapse from seaward rotation 
of the cap or toe

- return walls extending landward of the seaward face of the building or 
structure being protected and landward of the effects of erosion and scour

2.3.12 Drainage and Drainage Structures

The BPAT observed the remains of several new stormwater discharge structures 
adjacent to or between multifamily buildings. These structures consisted of 
large-diameter corrugated plastic pipes, probably intended to carry stormwater 
runoff from parking areas and other impervious areas to the beach.  
Unfortunately, the seaward portions of these pipes were destroyed during the 
storm and their pre-storm configurations are not known with certainty.

It did appear, however, that erosion beneath habitable structures near these 
damaged discharge pipes was more severe than at areas away from the pipes, 
possibly a result of direct discharge of upland stormwater runoff adjacent to or 
beneath the habitable structures. It is likely that the pipes failed because of 
erosion and scour caused by the storm or because of the loss of protective 
seawalls and bulkheads. It is possible, but not known for certain, that the pipe 
failures and discharge adjacent to the multifamily buildings contributed to 
foundation damage at those buildings.

2.4 Incorporation of Pre-FIRM Construction into New Construction

Many single-family structures appeared to have been constructed above or 
adjacent to portions of older pre-FIRM structures and probably resulted from 
efforts to expand and/or reconstruct older, smaller structures. This type of 
construction is vulnerable to storm damage because the foundations of the pre-
FIRM and post-FIRM sections can respond differently to storm forces and erosion. 
For example, the BPAT found a damaged house in Mexico Beach that was supported 
by two types of foundations. One part of the house was supported on concrete 
block piers placed on the old pre-FIRM slab-on-grade. The remainder of the 
house, which extended beyond the original pre-FIRM footprint, was supported on 
timber piles set in concrete encasements. Although the piles and slab survived 
the storm, the concrete block piers did not. With the loss of the piers, the 
house listed to the unsupported side and the floor beams separated from the 
newer, pile foundation. Had the entire house been supported on timber piles, it 
may have survived with little or no damage.

2.5 Design, Construction, and Workmanship

After observing hundreds of damaged or destroyed structures, the BPAT has 
concluded that many structures seem either to have been built without the aid of 
detailed design plans (prepared by a design professional) or not to have been 
built in accordance with plans that were available. Failure of non-engineered or 
poorly designed foundations, structural systems, and critical connections often 
led to major damage or complete loss of structures. Such losses are preventable.

Numerous instances of poor workmanship were also noted by the BPAT during its 
inspections. In particular, the BPAT found several examples of misalignment of 
timber foundation piles and poor framing practices in platform-type 
construction. The BPAT also noted recurring problems with concrete construction. 
For example, reinforcing steel was missing from or misplaced in slabs, footers, 
and wall grade beams, and welded wire fabric reinforcement was frequently at the 
bottom of, not centered in, the slabs. Although no damage was observed that 
could be definitively linked to these examples of poor workmanship, such 
practices should be avoided in any construction, especially in areas subject to 
coastal storm forces.





3 RECOMMENDATIONS

The BPAT’s recommendations are presented below. Engineering design drawings are 
also presented that illustrate the recommendations and provide details that can 
be used to enhance building performance under hurricane and coastal flood 
conditions.

3.1 Application of V-Zone and A-Zone Design and Construction Requirements

NFIP V-Zone construction requirements specify that new construction be elevated 
on piles, posts, columns, or piers and that the bottom of the lowest horizontal 
structural member (e.g., floor beam, joist) be at or above the BFE. Depending on 
the dimensions of those structural members, the resulting lowest floor 
elevations can be as much as 1.5 feet above the BFE. By comparison, NFIP A-Zone 
standards for new construction require that the lowest floor of the structure be 
at or above the BFE.

FIRMs accounting for wave effects were adopted by the communities in the study 
area between 1985 and 1987, prior to changes in V-Zone mapping procedures that 
extended coastal V-Zones to the landward toe of the primary frontal dune. The 
BPAT believes that this factor, coupled with a decade of long-term erosion, 
resulted in narrow V-Zones and an underestimation of actual risk along or near 
the shoreline, which increased the exposure of some post-FIRM A-Zone 
construction to V-Zone flood forces.

3.1.1 FEMA to Issue Revised FIRMs

FEMA will address the V-Zone issue discussed above by completing restudies and 
revisions to the FIRMs as necessary for the communities in the study area. 
Preliminary revised maps for the affected communities will not be completed 
until 1997; thus, the majority of post-Opal reconstruction will be governed by 
the FIRMs in effect at the time of the storm and by State CCCL requirements. 
Until the revised FIRMs are completed, the affected communities should consider 
studying local coastal flooding conditions that occurred during Hurricane Opal 
to determine whether areas in coastal A-Zones, as well as areas within several 
hundred feet of the Gulf of Mexico shoreline, are actually subject to V-Zone 
flood forces. If such areas are identified, the affected communities should 
strongly encourage the owners of new construction and substantial improvements 
to existing structures within those areas to conform with V-Zone construction 
standards and to provide several feet of freeboard above the BFEs shown on the 
current FIRMs.

3.1.2 Communities Using Higher Standards in Coastal A-Zones

The benefit of applying more stringent requirements to new construction in 
coastal A-Zones in the study area was illustrated by the performance of recent 
post-FIRM A-Zone construction in the City of Pensacola Beach during Hurricane 
Opal. Under the jurisdiction of the Santa Rosa Island Authority (SRIA), the city 
enforces V-Zone construction standards in all of the barrier island areas shown 
as A-Zones on its current FIRM. Within the same A-Zones, the SRIA also requires 
that the lowest horizontal structural member of all new construction be at or 
above an elevation of 10 feet NGVD. Therefore, the lowest floor elevation would 
be approximately 11.5 feet NGVD or higher. The A-Zone BFE ranges from a minimum 
of 6 feet NGVD to a maximum of 10 feet NGVD. Therefore, the SRIA’s requirement 
results in lowest floor elevations up to 5.5 feet higher than what would 
otherwise be obtained. During Hurricane Opal, flooding occurred in V-Zone and A-
Zone areas shown on the city’s FIRM. Recent post-FIRM A-Zone construction 
generally performed well, as evidenced by the survival of elevated structures in 
A-Zones and the destruction of nearby pre-FIRM, at-grade structures. The BPAT 
believes that the higher elevations of lowest floors, coupled with the 
requirement for construction on piles, helped to significantly reduce the extent 
of damage in the city’s barrier island A-Zones.

Communities that are considering adopting more restrictive requirements in their 
coastal A-Zones, such as V-Zone construction requirements or freeboard 
requirements, may want to contact the FEMA Region IV Office or the State of 
Florida Department of Community Affairs for technical assistance. Communities 
should also consider that by adopting these more restrictive requirements, they 
can earn community-wide reductions in flood insurance premiums under the NFIP’s 
Community Rating System. In addition, lower flood insurance premiums can be 
obtained for individual structures when the structures are built to provide 
freeboard above the BFE. Such structures, if designed and constructed in 
accordance with the NFIP requirements, will receive lower premiums in 1-foot 
increments for up to 4 feet of freeboard above the BFE.

Communities are encouraged to reexamine foundation design requirements for 
structures in areas near the Gulf of Mexico shoreline in light of damage caused 
by Hurricane Opal. Structures in these areas should be designed to withstand all 
anticipated flood, erosion, debris, and wind forces. Foundation designs for 
structures in A-Zones, B-Zones, C-Zones, and X-Zones should be considered 
carefully to ensure that the designs reflect actual risks. Therefore, the BPAT 
recommends that communities and individuals consider the following:

- For all areas subject to high-velocity wave action, strong currents, erosion, 
or combinations thereof — regardless of flood zone designation — the embedment 
depths specified for pile foundations should be sufficient to ensure that the 
foundation will withstand anticipated erosion, conical scour, and storm forces.

- Foundations for masonry columns should be designed to withstand all 
anticipated flood, erosion, conical scour, debris, and wind forces. Shallow 
footings should not be used to support masonry columns where the risk of 
undermining exists.

- In areas known to be subject to storm-induced scour and erosion, any slabs 
serving as floors for habitable spaces should be designed and constructed to 
withstand all anticipated erosion, scour, and storm forces. Therefore, if the 
potential for undermining exists, slabs should be designed and constructed as 
structural slabs and attached to sufficient foundation systems that do not rely 
on underlying soil for support.

- In areas known to be subject to storm-induced scour and erosion, slabs used 
solely for parking should not be attached to structural members and should be 
designed and constructed to break into small pieces in the event of undermining, 
thereby minimizing potential transfer of flood loads to the structure.

3.2 Permitting, Plan Review, and Inspection

From the nature and extent of damage observed during its inspections, the BPAT 
has concluded that the quality of new construction can and should be improved. 
The specific recommendations of the Hurricane Opal BPAT regarding this issue, 
listed below, are similar to recommendations made by the BPAT that assessed 
damage resulting from Hurricane Andrew (FEMA 1992).

- Designers, building officials, and contractors must ensure that all 
anticipated storm forces are taken into consideration and must avoid practices 
that have led to common building failures. Most building failures are 
predictable from the actual performance of similar structures during previous 
storms. Communities may want to consider requiring designers and contractors, 
through certification, registration, or continuing education, to demonstrate 
knowledge of all anticipated storm loads (e.g., wind, flood, debris, erosion) 
and proper design and construction methods that enable structures to withstand 
those forces.

- Quality of construction workmanship should be improved. Contractors and 
subcontractors should construct strictly according to design plans, and they 
should not attempt to compensate for changed site conditions or construction 
flaws and errors with non-engineered adjustments and repairs. Attempts to devise 
and implement rapid fixes to construction problems may render a structure 
vulnerable to storm forces and may lead to structural damage or destruction. 
Field representatives of building departments should require that plans be 
resubmitted when such concerns are identified in the field.

- Permitting, plan review, and construction inspection procedures should be 
improved. The knowledge and training of reviewers and inspectors should be 
enhanced through certification or continuing education. Building departments 
would need sufficient financial and human resources to ensure that frequent and 
comprehensive inspections occur during construction. Plan review and 
construction inspection tasks should make greater use of licensed design 
professionals. This could be accomplished through various combinations of public 
and private sector responsibilities. For example, a community with adequate 
resources could employ design professionals to support both plan review and 
construction inspection. Alternatively, a community could require that engineers 
and architects of record assume greater responsibility for monitoring and 
inspecting construction. The latter approach was taken in Dade County, Florida, 
after the Hurricane Andrew disaster.

3.3 Construction Materials

All materials should meet or exceed the minimum requirements for building 
materials in the Standard Building Code. All materials subject to flooding 
should resist damage, deterioration, corrosion, and decay due to inundation, 
precipitation, wind-driven water, salt spray, or other corrosive agents. 
Guidance concerning flood- and corrosion-resistant materials can be found in 
FEMA’s Technical Bulletin 2-93, Flood-Resistant Materials Requirements for 
Buildings Located in Special Flood Hazard Areas (FEMA 1993b) and Technical 
Bulletin 8-96, Corrosion Protection for Metal Connectors in Coastal Areas (FEMA 
1996). For example:

- Special consideration should be given to structural connectors such as 
hurricane straps and hangers to ensure they are specified properly and that 
precautions are taken with metal structural components to ensure that structural 
integrity is not compromised by corrosion (FEMA 1996).  
• Where used to provide structural support for elevated structures, laminated or 
structural composite beams and joists should be properly specified, 
manufactured, treated, and installed for exterior use to avoid deterioration, 
delamination, or other problems that may result from use of members intended for 
interior use. Furthermore, designers and contractors should employ connections 
and connectors recommended by the American Institute of Timber Construction and 
allowed by the local building code, since standard connections and connectors 
used with sawn lumber may not be appropriate for laminated or composite lumber. 

- Asphalt roofing shingles should be of sufficient size and weight to meet wind 
resistance requirements in the applicable building code. Roofing tiles should be 
properly nailed, screwed, or fastened in accordance with the manufacturer’s 
recommendations. 

- Metal roofing should be properly fastened to reduce damage, which tends to be 
progressive — a small defect can result in loss of the entire metal roof.

3.4 Repair and Retrofit of Damaged Structures

Repairs of damaged structures should be completed in accordance with applicable 
codes and regulations and should be inspected to ensure conformance to the 
applicable building code and floodplain management requirements. Designers and 
contractors should be reminded that if a structure is damaged to the point that 
the cost of repairing it to its pre-damage condition equals or exceeds 50 
percent of its pre-damage market value, repair will be governed by local, State, 
or NFIP substantial damage regulations, as adopted by community floodplain 
ordinance.

Opportunities to retrofit damaged structures should also be aggressively 
pursued. Elevation, relocation, floodproofing, and installation of protective 
structures should be considered as effective means of reducing future damages 
(Florida Department of Community Affairs 1995). Where possible, retrofitting 
measures should be passive measures that do not require human intervention.

3.5 New Construction and Substantial Improvements

In V-Zones, construction plans for all new and substantially improved structures 
must be signed and sealed by a registered design professional. The BPAT 
recommends that in coastal A-Zones, plans for new and substantially improved 
structures also be signed and sealed by a registered design professional. 
Consideration should be given to having building setbacks from the shoreline and 
first floor elevations exceed minimum requirements where current FIRMs and 
construction setbacks do not reflect the actual flood levels, erosion, scour, 
and storm effects experienced during Hurricane Opal.

3.5.1 Pile, Post, Column, and Pier Foundations

Pile, post, column, and pier foundations should be designed to accommodate all 
design flood, wind, and other loads acting simultaneously in accordance with the 
requirements of ASCE 7-95, Minimum Design Loads for Buildings and Other 
Structures (ASCE 1995). Documented amounts of erosion and conical scour from 
Hurricane Opal and earlier storms should be considered in the determination of 
foundation embedment. When cast-in-place concrete piers are poured, measures 
should be used to prevent sand or earth from collapsing into the excavation and 
reducing the pier cross-section. Figure 3-1 shows the survival of a structure 
built on a well-constructed concrete pile foundation that sustained severe 
erosion. Figures 3-2 through 3-9 show recommended pile, post, column, and pier 
foundation designs. While there were no failures observed of spliced wood piles 
(see Figure 2-8), the recommended practice is to install foundation elements in 
a continuous length (i.e., in one piece).

[Begin figures]
Figure 3-1 is a photo showing how this well-constructed concrete structure 
survived the storm with little or no damage, even with 5 feet erosion.

Figure 3-2 is an illustration showing how posts are placed in excavated holes 
and may be anchored in the concrete pad at the bottom of the hole. Where 
possible, lateral bracing should be oriented parallel to the anticipated flow 
path (FEMA 1993a).

Figure 3-3 is an illustration showing how posts can also be anchored in concrete 
encasements. Where possible, lateral bracing should be oriented parallel to the 
anticipated flow path (FEMA 1993a).

Figure 3-4 is an illustration showing a post on concrete bearing pad. Soil depth 
below maximum potential depth of scour is adequate to withstand lateral and 
vertical loads during the base flood (after FEMA 1993a).

Figure 3-5 is an illustration showing a post on earth bearing. Soil depth below 
maximum potential depth of scour is adequate to withstand lateral and vertical 
loads during the base flood (after FEMA 1993a).

Figure 3-6 is an illustration showing an anchorage of post. Soil depth below 
maximum potential depth of scour is adequate to withstand lateral and vertical 
loads during the base flood (after FEMA 1993a).

Figure 3-7 is an illustration showing how piles are mechanically driven into the 
ground and are therefore less susceptible to high-velocity flooding, erosion, 
conical scour, and pullout. Where possible, lateral bracing should be oriented 
parallel to the anticipated flow path (FEMA 1993a).

Figure 3-8 is an illustration showing how the depth of pile embedment provides 
stability by enabling the pile to resist lateral and vertical loads through 
passive earth pressure. Soil depth below maximum potential depth of scour is 
adequate to withstand lateral and vertical loads during the base flood (after 
FEMA 1993a).

Figure 3-9 is an illustration showing a post/pile foundation. Soil depth below 
maximum potential depth of scour is adequate to withstand lateral and vertical 
loads during the base flood (after FEMA 1993a).
[End figures] 

3.5.2 Slabs and Grade Beams

With the exception of at-grade parking slabs, slabs-on-grade in areas known to 
be subject to storm-induced erosion and scour should be designed as freestanding 
structural elements and reinforced to withstand the loss of underlying soil. 
Freestanding structural slabs should be designed and constructed to withstand 
all flood, wind, and debris forces acting simultaneously (in accordance with 
applicable standards and codes) and to minimize debris trapping.

Grade beams should be designed as freestanding structural elements that are 
reinforced to withstand the loss of underlying soil, to withstand all flood, 
wind, and debris forces acting simultaneously, and to minimize debris trapping. 
The design of other structural components must consider the hydrodynamic and 
other forces that will act on grade beams and structural slabs once they are 
exposed to flood forces by storm-induced erosion and scour.

3.5.3 Framing Systems

Framing systems should be designed to support all anticipated loads, and any 
cutting of holes for electrical lines, ductwork, or plumbing piping must be in 
accordance with code requirements. Framing systems should not be compromised by 
the excessive or improper drilling or cutting of holes. If such drilling or 
cutting is necessary, additional support may be required to return the structure 
to its design strength. It is also important that proper bracing and fire stops 
be included.

3.5.4 Connections
All metal connectors should, at a minimum, be constructed of hot-dip galvanized 
steel and should conform to the Standard Building Code specifications; the 
guidance provided in FEMA’s Technical Bulletin 8-96, Corrosion Protection for 
Metal Connectors in Coastal Areas (FEMA 1996); and any other requirements 
specified by the design professional of record. Metal connectors include the 
following:

- wood-to-wood anchors and angles, caps and bases, hangers, and structural 
connectors

- wood-to-masonry foundation straps, masonry hangers, purlin anchors, plates, 
tension ties, truss anchors, and brick anchors

- wood-to-concrete anchors and holddowns; bases for beam seats, post bases, and 
truss seats; hangers; and wedge shims.
Wood should not be used as a shim material since it is subject to compression 
and may lead to connection failure; instead, metal, brick, or mortar can be 
used.

3.5.5 Bracing

It is preferable that structures be designed with deep foundations to withstand 
all anticipated loads without reliance on bracing. However, where used to 
provide additional stiffening, bracing should consist of hot-dip galvanized 
steel rods threaded on both ends and joined in the center with a turnbuckle (see 
Figure 2-10). Alternatively, wood bracing can be used if it is properly designed 
and attached to piles with bolts. All bracing should be designed as part of the 
structure by the designer to survive hydrodynamic and debris impact forces 
generated by the base flood.

3.5.6 Breakaway Construction, Free-Of-Obstruction, and Enclosure Requirements 
Under the NFIP

In general, recently constructed breakaway walls in Coastal High Hazard Areas 
(V-Zones) and seaward of the CCCL performed well.  However, State and local 
building officials and floodplain administrators should be aware of and should 
prevent two problems noted during post-Opal damage assessments: (1) breakaway 
walls attached to walls and other structure elements above the lowest floor and 
(2) attachment of utility lines and similar components to breakaway walls. In 
accordance with V-Zone requirements:

- Breakaway walls and panels below an elevated structure must be separate and 
distinct from walls and construction above the lowest floor elevation. These 
sections are intended to break free and must be able to do so without damaging 
upper walls, sheathing, cladding, and other components.

- No wiring, conduits, plumbing, or utility components may be placed behind or 
fastened to breakaway walls or panels.

- Areas below an elevated building should be designed and constructed in 
accordance with FEMA’s Technical Bulletin 5-93, Free-Of-Obstruction Requirements 
for Buildings Located in Coastal High Hazard Areas (FEMA 1993c).

Figures 3-10 and 3-11 show recommended designs for breakaway wall systems.

[Begin figures]
Figure 3-10 is an illustration showing a wood stud breakaway wall (after FEMA 
1986).

Figure 3-11 is an illustration showing a light-gauge metal stud breakaway wall 
(after FEMA 1986).
[End figures]

3.5.7 Stairs, Decks, and Porches

These structures are frequently damaged by floods and storms. Much of this 
damage can be prevented by the application of a few simple techniques:

- Support elevated decks on piles rather than posts or piers. If a pile 
foundation is not used for the deck, use knee bracing connected to the 
foundation piles that support the main structure; however, do not notch the 
foundation piles to seat the knee bracing.

- Design and construct stairs to hinge at the top, so they can be raised prior 
to a storm.

- Design and construct fixed steps and walkovers with piles and sturdy 
structural members. Consider steps and horizontal decks to be sacrificial, and 
construct them so that they will break loose in small sections when acted on by 
flood forces.

3.5.8 Utilities

All utility components (including electric meters) should be located on the 
landward side of the structure and, according to NFIP requirements for V-Zones, 
must be elevated to or above the BFE and anticipated flood level (including wave 
effects and runup) whenever possible. In A-Zones, utilities may be below the BFE 
provided that the CCCL requirements are also adhered to. Utility components 
below the BFE should be contained in floodproof enclosures.  Figures 3-12 and 3-
13 show recommended designs for mechanical platforms

[Begin figures]
Figure 3-12 is an illustration of cantilevered floor joists as a retrofit for an 
elevated home to allow for a mechanical balcony.

Figure 3-13 is an illustration showing the installation of a mechanical balcony 
as a retrofit for an elevated home.
[End figures]

3.5.9 Seawalls and Erosion Control Structures

Although permitted in many states and jurisdictions, seawalls, bulkheads, and 
other erosion control structures should not be relied on to contain soil 
required for support of a habitable structure. The structure should be supported 
on a foundation that can withstand or accommodate erosion and loss of support.
Where used, seawalls, bulkheads, and erosion control devices should be designed 
to resist failure due to wave and flood forces, overtopping, undermining, and 
debris impact. Wing walls or return walls should extend landward to a point 
beyond that affected by storm-induced erosion.





4 REFERENCES

American Society of Civil Engineers, 1995. ASCE 7-95, Minimum Design Loads for 
Buildings and Other Structures. Washington, DC.

Federal Emergency Management Agency, 1986. Coastal Construction Manual, FEMA-55. 
February 1986.

Federal Emergency Management Agency, 1992. Building Performance: Hurricane 
Andrew in Florida — Observations, Recommendations, and Technical Guidance, FIA-
22. Federal Insurance Administration. Washington, DC. December 21, 1992.

Federal Emergency Management Agency, 1993a. Building Performance: Hurricane 
Iniki in Hawaii - Observations, Recommendations, and Technical Guidance, FIA-23. 
Federal Insurance Administration. Washington, DC. January 29, 1993.

Federal Emergency Management Agency, 1993b. Flood-Resistant Materials 
Requirements for Buildings Located in Special Flood Hazard Areas, Technical 
Bulletin 2-93. Washington, DC.

Federal Emergency Management Agency, 1993c. Free-Of-Obstruction Requirements for 
Buildings Located in Coastal High Hazard Areas, Technical Bulletin 5-93. 
Washington, DC.

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

Florida Department of Community Affairs, 1995. Retrofitting and Flood Mitigation 
in Florida. Division of Emergency Management. Tallahassee, FL.

Florida Department of Environmental Protection, 1995. Hurricane Opal: Executive 
Summary of a Report on Structural Damage and Beach and Dune Erosion Along the 
Panhandle Coast of Florida. Bureau of Beaches and Coastal Systems. Tallahassee, 
FL.

Michael Baker Jr., Inc., 1995. Hurricane Opal Florida Panhandle Wind and Water 
Line Survey. Prepared for the Federal Emergency Management Agency and Property 
Loss Research Bureau. October 1995.

National Oceanic and Atmospheric Administration, 1995. Hurricane Opal, 
Preliminary Best Track and Maximum Sustained 1-min Surface Winds. AOML, 
Hurricane Research Division. Miami, FL.

Panama City News Herald, 1995. “Estimated Insured Losses from Hurricane Rises to 
$1.5 Billion.” October 13, 1995, p. 3c.





APPENDIX

Building Performance Assessment Team Members

Mark A. Vieira, P.E. 
Civil Engineer 
Mitigation Division
Federal Emergency Management Agency, Region IV
Atlanta, GA

Tony Sandifer
Mitigation Division
Federal Emergency Management Agency, Region IV
Atlanta, GA

Donald R. Beaton, Jr.
Chief Underwriter
Federal Insurance Administration
Federal Emergency Management Agency
Washington, DC

Joseph E. Pelczarski
Federal Emergency Management Agency, Region I
Boston, MA

Sanjay Mane
Civil Engineer
Florida Department of Community Affairs
Tallahassee, FL

Charles R. Weeks, P.E.
President
The Wainscot Company
Pensacola, FL

J. Paul Hoofnagle
Senior Civil Engineer
Greenhorne & O’Mara, Inc. 
Greenbelt, MD

Christopher P. Jones, P.E.
Senior Coastal Engineer
Earth Tech, Charlottesville, VA