Several construction techniques have been shown to improve the resistance of homes to high wind events such as less-severe (EF0-EF2) tornadoes, which are 95% of all tornado events, and intense hurricanes. The Insurance Institute for Business & Home Safety (IBHS) tests under controlled wind tunnel conditions, and both IBHS and the Engineered Wood Association (APA) conduct post-storm assessments to collect data on what performs well in these conditions.
Homes built to the International Residential Code® (IRC®) perform well in high-wind events. However, by focusing on additional strategies to strengthen the roof and provide a continuous load path through the structure to the foundation, builders can provide consumers in areas at high risk of tornadoes and intense hurricanes with homes that will perform even better than a code-compliant home, potentially allowing consumers to remain in their home after a severe storm event and reducing repair costs. These strategies begin in the design phase with material selection and come together with attention to detail during construction.
Sealing the Roof
Keeping air from getting underneath the roof components is key to preventing high winds from tearing off the roofing material and possibly causing catastrophic destruction of the home. IBHS looked at homes in Florida after Hurricane Michael and found those with sealed roof decks fared better. Construction techniques contributing to stronger roofs include taping the roof deck seams, using tighter nail spacing to fasten roof decking to trusses and rafters, and properly fastening drip edges and gutters to minimize the ability of the wind to get up underneath roof covering. Details — such as using ring shank nails A and upgrading the underlayment to 30lb felt, or to a self-adhered or synthetic underlayment — can further improve the resistance of homes to high winds and intense rainfall.
Providing a Continuous Load Path
Wind acting on a home subjects it to several types of load:
- Uplift pressure, which can pull off the roof;
- Shear loads, which can cause racking (leaning); and
- Lateral loads, which can cause the home to slide off the foundation, or even overturning the home.
Using wood structural panels or other structural sheathing permitted by the IRC® as wall bracing can provide protection against racking, and anchors against base shear and hold-downs against overturning. Constructing a continuous load path — connections that tie the floor, walls and roof together — can make it harder for high wind forces to tear a home apart. The graphic from IBHS illustrates typical connection points to protect against uplift.
A recent NAHB study showed that consumers' willingness to pay for these hardening strategies depends on their awareness of the risk(s), while the amount they are willing to pay depends on the risk and on household income. For example, consumers with annual household incomes of $50,000 to $100,000 were willing to pay $1,800 (median value) to mitigate risk from tornadoes and $1,000 (median value) to mitigate risk from hurricanes. This information can be used by builders to inform discussions with their clients as appropriate for their geographical areas and markets.
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