Why is it important for homebuilders to understand wind movement and the impact wind has on homes? Consider these statistics: Roughly 1/3 of the U.S. is threatened by high winds. On average, more than 1,000 tornadoes are reported every year. The number of hurricanes per year has reached record levels. And, in recent years, damage from high winds has not only become the leading cause of property loss, it also exceeds the combined total losses of all other natural disasters in the country.
Wind can severely damage a home via uplift, racking, sliding, and overturning. Uplift occurs when the wind flows over the home’s roof, creating a lifting effect. It can separate the home from the foundation, the second story from the first story, and the roof from the home. Racking and sliding occur when the wind exerts pressure on the home’s side, causing it to tilt out of square or move off of its foundation. Overturning occurs when strong wind that is unable to rack or slide a home ultimately rotates the home off of the foundation. Wind also can cause damage indirectly via windborne debris that becomes destructive and deadly missiles.
Site location
The Best Practice for building a home that’s durable and safe from wind damage is for builders to know which wind zone they’re building in, and then fully implement local wind zone building requirements. For more information, FEMA provides a map of wind zones.
In addition to knowing the wind zone, it’s important for a builder to consider the site’s topography, ground roughness, and site exposure. These 3 elements can intensify or minimize the wind’s effect on a home. Consider topography, for example: wind speed increases as it passes over or between hills and through valleys, hence the “wind tunnel” effect felt in cities with many tall buildings. Conversely, wind speed slows as it goes over rough terrain, caused by a drag effect. The shape of the hills and valleys and the amount of shelter upwind also have an effect on the wind speed over a site. Finally, site exposure, which is determined by the protection provided by other buildings or natural obstructions, influences the wind’s impact on a home. Sheltered sites enjoy more wind protection than exposed sites, and most suburban developments on flat or gently sloping topography are considered “sheltered” sites.
Protection against wind
Knowing the wind zone and wind-impacted site conditions for a home will help you to design and orient a home to take advantage of the site’s natural assets. It will also help you to choose the best materials and construction methods to ensure the home is strong enough to withstand the elements. In addition, using appropriately durable materials may mean that less maintenance is required or that the materials will not need to be replaced as soon.
Local building codes also can help with wind protection. They specify material types and thicknesses as well as locations, types, and numbers of fasteners required for the minimum protection for the foundation, floor and wall framing, roof, and more. In high-wind areas, codes also will focus on protecting the home’s openings, such as garage doors, because approximately 80% of residential hurricane damage starts with wind entry through garage doors. For the best protection, consult an architect or professional engineer, in conjunction with local building codes, to determine each home’s individual requirements.
More Best Practices® for planning, designing and constructing your homes to manage wind and other natural forces can be found in BuildIQ University’s online training course, Building for Performance.
