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Frequently Asked Questions About Building Science: Wind

Find answers to frequently asked questions regarding FEMA Building Science Wind guidance, or see our other Building Science FAQ collections.

If you need additional information, please email the FEMA Building Science Helpline or call at 866-927-2104.

Wind Guidance

How can I protect the roof of my home from water intrusion?

Installation of a secondary water barrier (SWB) over the structural wood panel sheathing can help prevent water intrusion, even when shingles are blown off of the roof. The SWB should be applied after the roof deck has been adequately strengthened and before a new roof covering is installed. Technical Fact Sheet No. 7.2 in FEMA P-499, Home Builder’s Guide to Coastal Construction (FEMA 2010a), provides guidance on how to install a SWB beneath asphalt shingle roof coverings. Although not specifically addressed, builders can also use Technical Fact Sheet No. 7.2 as guidance on installing SWBs over wood board decking.

Section 4.1.1.2 of FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010b), offers several alternatives to installing underlayments for shingle roofs, metal roofs, and concrete and tile roofs. FEMA P-804 also discusses installing new roof coverings (Section 4.1.1.3). Proper installation of roof coverings is necessary to avoid their being ripped from the home during a high-wind event.

Additional guidance for optimizing roof performance can be found in Technical Fact Sheets No. 7.1 through 7.6 in FEMA P-499 and in Section 12.7.5 of FEMA P-55, Coastal Construction Manual (FEMA 2011).

The use of spray polyurethane foam (SPF) adhesive is another option. As described in Section 4.1.2 of FEMA P-804, SPF adhesive can be applied to the underside of a roof deck at the joints between the roof sheathing panels and along all intersections between the roof deck and framing members. The application of SPF in this case serves two purposes: the connection between the roof deck and supporting structural members is enhanced, and the SPF seals the joints of the roof deck to prevent water intrusion. SPF is not, however, as effective as installing an underlayment, but may be considered when not replacing the entire roof covering.

As always, the manufacturer’s instructions should take precedence oversupersede all recommendations given in FEMA publications.

References:

  • FEMA. 2010a. Home Builder’s Guide to Coastal Construction. FEMA P-499. Washington, DC. December 2010.
  • FEMA. 2010b. Wind Retrofit Guide for Residential Buildings. FEMA P-804. Washington DC. December 2010.
  • FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.

How can the wind and water resistance of roof soffits in homes be improved?

Technical Fact Sheet No. 7.5 in FEMA P- 499, Home Builder’s Guide to Coastal Construction (FEMA 2010a), provides retrofit criteria for each type of attic ventilation opening, including soffits. The most critical soffit installations are those with vinyl or aluminum soffit panels. Aluminum soffit panels may also be vulnerable because of aluminum’s corrosion potential in an environment with salt-laden air. If the house is within 3,000 feet of a body of water that produces salt spray, it is recommended that aluminum soffits be completely removed and replaced with a soffit system installed per the guidance of Technical Fact Sheet No. 7.5. Furthermore, Figure 4-12 of FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010b), shows a typical soffit detail for retrofitting existing soffits to improve wind and water resistance. It should be noted that while many homes may have different soffit configurations than shown in Figure 4-12, the basic intent of the retrofit in the figure—reduction of long spans by installation of intermediate supports and application of continuous edge support—should be applied in any situation. For improved wind and water resistance, soffits should be secured using sealant and screws as described in Technical Fact Sheet No. 7.5. The selected soffit product may have more restrictive installation instructions when installed in high-wind regions, in which case the more restrictive installation method should be followed.

References:

  • FEMA. 2010a. Home Builder’s Guide to Coastal Construction. FEMA P-499. Washington, DC. December 2010.
  • FEMA. 2010b. Wind Retrofit Guide for Residential Buildings. FEMA P-804. Washington DC. December 2010.

Are there any wind-related building code requirements or design standards pertaining to the attachment of rooftop equipment?

Rooftop equipment is typically torn off in high winds because equipment anchorage to the roof is inadequate, the strength of the equipment is inadequate, or the equipment is corroded. FEMA P-55, Coastal Construction Manual (FEMA 2011), includes prescriptive attachment recommendations for small equipment (see Section 12.8.2.1). Such equipment may include exhaust fans, vent hoods, and some residential air conditioning units. FEMA P-55 also provides guidance on job-site strengthening of fan hoods and cowlings through the use of stainless steel cables.

If the mounted equipment is more than 30 inches above the curb, the attachment design should be based on the calculated wind loads from ASCE 7-10, Minimum Design Loads for Buildings and Other Structures. Chapter 29 of ASCE 7-10 contains provisions for determining the lateral force and vertical uplift force on rooftop equipment for buildings with a mean roof height less than or equal to 60 feet. Figure 29.5-1 of ASCE 7-10 provides a force coefficient for chimneys, tanks, rooftop equipment, and similar structures. The force coefficient, Cf, is applied to equations found in Section 29.5.1 of ASCE 7-10 to calculate both the lateral and uplift design wind forces. The lateral force is based on the vertical area of the equipment as projected on a vertical plane perpendicular to the direction of the wind. The uplift force is based on the horizontal area of the equipment as projected on the horizontal plane above the equipment and parallel to the direction of the wind.

To avoid corrosion problems, FEMA P-55 (Section 12.8.2.1) recommends nonferrous metals, stainless steel, or steel with a minimum G-90 hot-dip galvanized coating for the equipment itself, equipment stands, and equipment anchors when located within 3,000 feet of a body of water producing salt spray. Stainless steel fasteners are also recommended.

References:

  • ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE 7-10, Reston, VA, May 2010.
  • FEMA. 2011. Coastal Construction Manual. Washington, DC. FEMA P-55. August 2011.

Does FEMA have any publications that address design and construction guidance for high wind?

FEMA has several publications that address high-wind hazards. The following publications are useful references on residential construction in high-wind areas:

  • FEMA P-320. Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business. Washington, DC. August 2014.
  • FEMA P-550. Recommended Residential Construction for Coastal Areas: Building on Strong and Safe Foundations. Washington DC. December 2009.
  • FEMA P-499. Home Builder’s Guide to Coastal Construction: Technical Fact Sheet Series. Washington, DC. December 2010.
  • FEMA P-804. Wind Retrofit Guide for Residential Buildings. Washington, DC. December 2010.
  • FEMA P-55. Coastal Construction Manual. Washington, DC. August 2011.

FEMA also has many publications that address the high-wind hazard for non-residential construction:

  • FEMA P-424. Design Guide for School Safety in Earthquakes, Floods, and High Winds. Washington, DC. December 2010.
  • FEMA 543. Design Guide for Improving Critical Facility Safety from Flooding and High Winds: Providing Protection to People and Buildings. Washington, DC. January 2007.
  • FEMA 577. Design Guide for Improving Hospital Safety in Earthquakes, Floods and High Winds: Providing Protection to People and Buildings. Washington, DC. June 2007.
  • FEMA P-361. Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms. Washington, DC. March 2015.

Other resources include:

  • ASCE 7. Minimum Design Loads for Buildings and Other Structures. American Society of Civil Engineers (ASCE) 2010.
  • ICC 600. Standard for Residential Construction in High Wind Regions. International Code Council (ICC) 2008.
  • ICC 500. Standard for the Design and Construction of Storm Shelters. International Code Council (ICC) 2014.
  • American Wood Council. Wood Frame Construction Manual Guide to Wood Construction in High Wind Areas for One- and Two-Family Dwellings (Exposure B versions for 90 mph, 100 mph, 110 mph, 120 mph, and 130 mph). 2006.
Last updated September 17, 2020