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Implementing the Wind-Resistant Openings Tech Set

Five steps to design, specify and install storm-resistant windows.

1. Consider Wind Zone and Exposure

Building codes contain maps detailing basic wind speeds that can be expected in any area of the United States over a 50-year mean recurrence interval. These are the starting point for calculating an exterior opening's exposure to pressures from high winds. In addition to design wind speed, a building is rated with an exposure classification which indicates the level of sheltering around the building. Exposure classifications range from A (city center with tall buildings surrounding) to D (flat, unobstructed area exposed to wind flowing over open water).

Because vast expanses of open land or water allow unobstructed wind movement, the best practice is to site windows on walls where natural landscape features, like tree buffers or dunes, protect them from direct wind. If tree buffers are created, plantings should be located farther away from the structure than their expected height at maturity.

Obstructions on a building's façade, like bay windows and cantilevered decks, create vortexes for wind movement. Where these architectural features are present, builders should ensure that cladding and structural attachments have been properly designed and attached.

2. Identify Window Products That Work for the Region

[IMAGE: Hurricane Shutters]A. Performance Classification

The building codes require all windows to meet wind-driven rain conditions under the testing standard "Voluntary Specifications for Aluminum, Vinyl (PVC), and Wood Windows and Glass Doors," AAMA/NWWDA 101/I.S.2. The standard establishes five classes of windows based on the (wind) design pressure (DP) that the window was tested to, as detailed in column 2 of Figure 2. A DP of 40 is equal to a 155-mph wind. Determine necessary design pressures from the Table of Equivalent Wind Velocities.

B. Impact Resistance

In addition to the force of wind and wind-driven rain, homes are often struck by airborne debris from compromised structures and landscaping during storms. Therefore, building codes also require that window and door products installed in homes in areas where winds exceed 110 miles per hour meet tests for impact resistance. The tests mimic the window, door, curtain wall, or protective covering being struck by gravel traveling at 80 feet per second (called small missiles) or a 2x4 stud traveling at 50 feet per second (called a large missile) and undergoing repeated strikes. The Florida Building Code (FBC) requires that windows in high wind zones located within 30 feet of the ground meet the large missile test criteria and those higher than 30 feet from ground level meet the small missile test criteria.

C. Energy Efficiency

In addition to resistance to high wind, windows should be selected for energy efficiency and function. The easiest way to select the most energy-efficient window for a climate is to choose one bearing the ENERGY STAR© logo. In the absence of that designation, windows can be selected based on their thermal and other properties. The National Fenestration Rating Council (NFRC) operates a voluntary labeling program which provides efficiency information to consumers.

3. Size Windows for Egress

Bedrooms and habitable sub-grade basements require windows sized for escape or entry (by rescue personnel) in the event of a fire. The International Residential Code (IRC) requires a minimum opening width of 20 inches with 5.7-square-foot minimum free area at a sill no higher than 44 inches from the floor. Depending on the manufacturer, this requirement can usually be met with a 26x48 or larger double-hung unit. It is important to consider that inoperable hurricane shutters, like homemade plywood coverings that are applied from the exterior, will impede quick exit or entry when in place, as will shutters that require power to operate if the power source goes out during a storm.

4. Follow Manufacturer's Installation Instructions

Ultimately the day-to-day and disaster mitigating performance of window and door components depends on competent installation. Manufacturers provide detailed installation instructions. In addition, the American Architectural Manufacturers Association (AAMA) has developed an Installer Training Qualification program for windows and doors that is based on ASTM E-2112, Standard Practice for Installation of Exterior Windows, Doors, and Skylights. Through the program, installers are trained and tested, then issued AAMA installation certification. This and trade contractor quality assurance programs assure builders that the units have been professionally installed.

5. Install Shutters and Other Temporary Coverings

Shutters or other temporary coverings can provide impact resistance to windows and other openings. Miami-Dade County has a searchable database of these products that comply with the FBC.

FEMA has created fact sheets for homeowners, such as Install Shutters or Plywood Window Covers, and Against the Wind (.pdf). The Federal Alliance for Safe Homes (FLASH) also has a publication on DIY opening covers.

Content updated on 8/7/2006

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