Wind Protection Information

Protecting Your Home from Severe Winds

Damaging winds accompany many types of severe weather, including:

 

  • Hurricanes. Intense hurricanes produce winds over 110 mph that can completely destroy a home.
  • Thunderstorms often produce damaging winds caused by downbursts, or rapid downward rushes of air. When the air hits the ground it is forced to spread out, creating straight-line winds of up to 100 mph. These damaging winds are often mistaken for tornadoes.
  • Tornadoes. The most intense tornadoes, packing winds up to 318 mph, have been known to completely remove homes from foundations and carry objects several hundred yards.

 

While the intensity of those forces will vary, the construction techniques used to protect your home from them will not.

 

This diagram shows a generalized effect of wind forces on a home. The arrows pointing toward the home indicate winds that are pushing on the surface. The arrows pointing away from the home indicate winds that are pulling on the surface.

 

Notice how wind forces impact every surface of your home, not just the ones facing the wind. In many cases, the pulling forces of wind are more critical than the push as evident by the loss of roof coverings in many severe wind events

 

Protecting Your Roof From Severe Wind Damage

 

The roof of your home is one of the most critical lines of defense in protecting your family, pets and possessions from the violent forces of wind. The roof system consists of the roof covering (asphalt shingles, tiles, etc.), the decking (plywood), and the framing (rafters, trusses, etc.).

 

  • Roof Covering. Install roof-covering products that have been tested to ASTM D 3161 for wind resistance; and UL 2218 for impact (hail) resistance. Be sure to specify these standards and look for labels on the product packaging because wind- and impact-resistant roofing products do not look much different than untested products.
  • Secondary Water Barrier. Install a self-adhesive waterproofing material, such as flashing tape, over the joints in your roof deck. This will provide an effective secondary layer of protection from rainwater in the event the roof covering is damaged or removed by hail or wind.
  • Underlayment. Make sure there is a layer of asphalt roofing felt underneath the roof covering. The felt acts as a drainage plane in the event water gets under the roof covering.
  • Roof Decking. Install 5/8-inch-thick plywood roof decking panels with 10d nails spaced at 4 inches on center around the perimeter and 6 inches on center over intermediate framing. This will greatly improve the impact and wind resistance of your roof.

 

Gabled Roofs vs. Hipped Roofs

 

Keeping the Roof from Blowing Off and Keeping the House on the Foundation.

 

A gabled roof can be characterized as a roof with two slopes that come together to form a ridge or peak. A hipped roof is one that slopes upward from all sides of a building. Due to aerodynamic properties and conventional construction techniques, most hipped roofs will perform better in windstorms than most gabled roofs.

 

The intersection of the gable (triangular portion of the wall beneath the sloping roof surfaces) and end wall is a particularly weak point of gabled roofs unless full-height stud, concrete or masonry walls are used. If you have a gabled end wall, one of the following techniques should be used.

 

  • Balloon framing of the gable end wall. The best technique is to use full height studs or solid masonry or concrete from the floor below all the way to the roof. This is often called balloon framing.
  • Brace the intersection of the gable and the end wall. This point must be braced as it is extremely susceptible to failure from high winds. The amount and type of bracing should be determined by a professional engineer or see the Blueprint for Safety™ Contractor's Field Manual.

 

Connections

Severe winds can subject your home's roof to high uplift forces strong enough to remove the entire roof system or portions of it. To mitigate its vulnerability to this type of damage, the roof system has to be adequately attached to the exterior walls of your home. Conventional framing methods that use toe-nail connections to secure the roof framing to the exterior walls are not strong enough in most cases. The use of hurricane straps or clips are the most effective method for securing the roof.

 

While the roof is one of the most critical lines of defense in protecting your home, all joints — roof-to-wall, floor-to-floor, and wall-to-foundation — must be secured to create a "continuous load path" to the building's foundation. Your home's ability to resist wind forces is only as good as its weakest link. The only sure way to create a wind-resistant home is to secure the connections as described below:

 

  • Roof-To-Wall Connections. Use straps or clips, in addition to toe-nails, to connect the roof to the exterior walls.
  • Floor-to-Floor connections. Make sure each floor is also connected to the floor below with straps or clips in addition to any other code required nailing schedule.
  • Wall-to-foundation connections. Exterior walls should be securely anchored to the foundation (slab-on-grade, stem-wall) through the use of anchor bolts or mud-sill anchors.

 

Protecting Your Home's Openings From Severe Wind Damage

 

Windows and doors are susceptible to damage from flying debris during severe windstorms. When windows and doors fail, the protective envelope of your home is breached. This allows debris, wind and wind-driven rain inside the home, potentially causing extensive damage to its contents and interior finishes.

 

Even more critical is the potential for internal pressurization. When windows and doors fail, the opening created in the building envelope allows wind to enter and push on all the interior walls and the roof. This internal pressurization is similar to what happens when a balloon is being filled with air. Coupled with the forces of wind outside the home, the increase in internal pressure can lead to a catastrophic failure. This scenario is depicted below.

 

Wind coming in through opening may raise the roof

 

To prevent internal pressurization and the entrance of wind-driven rain and debris, protect windows and doors, including garage doors, by covering them with hurricane shutters or installing impact-resistant windows and doors. Use products that have been tested to the following standards and are designated as such:

 

  • ASTM E 1886 and ASTM E 1996 
  • SBCCI SSTD 12 
  • Miami-Dade PA 201, 202 and 203

 

Emergency Board-Up Procedures

 

The Federal Alliance for Safe Homes (FLASH) recommends that you install tested and certified impact-resistant devices to provide the highest level of protection from windborne debris. However, in an extreme emergency where a temporary measure is the only option, FLASH recommends use of the following emergency board-up procedure:                                                                    

 

  • Measure and cut 5/8 inch, exterior grade plywood that will overlap the wall framing and cover windows and doors.
  • Attach the plywood to cover the opening with 10d common nails, 12d box nails, or 2 1/2-inch #8 wood screws. (If installed over masonry or stucco, vibration-resistant anchors should be used.)If the shortest dimension of the window or door is 4 feet or less, space fasteners at 6 inches on center.
  • If the shortest dimension of the window or door is more than 4 feet and less than or equal to 6 feet, space fasteners at 4 inches on center. Plywood shutters should not be used where the shortest dimension of the window or door exceeds 8 feet.

 

The Federal Alliance for Safe Homes' (FLASH®) Spring 2006 newsletter is now available for you to download.  This issue launches FLASH's 'Retrofitness' campaign and tells you how to retrofit your existing home against hurricanes. Learn the specific steps you can take to strengthen your roof and better protect your windows and doors from severe winds and rain.

 

Check it out at:  www.flash.org/resources/files/FinalSpring06BFSNews.pdf.

 

FLASH's Blueprint for Safety News, Vol. 4, Issue 2 - DIY Wind Inspection takes homeowners through a ten-step do-it-yourself home wind inspection.  Click on the link below to get started.  Please note:  Due to the number of graphics, this may take longer than usual to appear on your screen.  Also, if you want to print out this pdf newsletter, you may have to scale the pages to fit your printer margins.

 

DIY Wind Inspection:  www.flash.org/resources/file/2007BPFS_NewsDIYWindInspection.pdf