Winds of Change

The hurricanes that pounded the Gulf and Atlantic coasts in 2004 left contractors and their customers pondering how to avoid damage when the next storm blows through. "There's no better time than when rebuilding to incorporate construction changes that will make a property less vulnerable to wind or water," says Bill Carwile, federal coordinating officer for the Federal Emergency Management Age...

December 31, 2004

 

In the wake of Hurricane Charley, homeowners in Port Charlotte, Fla., learned the damage that high winds can do to a roof that has been built improperly or with the wrong materials.

 

A garage door without substantial vertical bracing can be the weakest point of a home, leading to extensive damage.
Data collected from major weather events such as Hurricane Andrew is providing new strategies and insights for fortifying homes against wind damage such as this.
Using thicker plywood and ring shank nails instead of common roofing nails can provide greater wind resistance in a hurricane, according to FEMA.

 

The hurricanes that pounded the Gulf and Atlantic coasts in 2004 left contractors and their customers pondering how to avoid damage when the next storm blows through. "There's no better time than when rebuilding to incorporate construction changes that will make a property less vulnerable to wind or water," says Bill Carwile, federal coordinating officer for the Federal Emergency Management Agency.

Unfortunately, homeowners typically don't focus on preparing for the next storm, says Dennis Shea, the assistant secretary for policy development and research at the U.S. Department of Housing and Urban Development.

"Many times, homeowners in a rush to return to their homes do not take advantage of strategies, technologies or approaches that would improve the long-term performance of their homes," he says.

Whether you are rebuilding after a disaster or doing a regular remodel in a hurricane- or tornado-prone area, here are some of the innovations PATH, which is sponsored by HUD, recommends.

Raising the roof quality

The best place to start is the roof because it is the first line of defense against water, says Shea. He suggests looking at both shingles and sheathing. Replacing old shingles with new wind- and impact-resistant asphalt shingles, available from a variety of manufacturers, is a relatively simple upgrade. Almost all of these premium shingles maintain their integrity - and remain attached to the roof sheathing - in winds of more than 100 mph.

"That's certainly better than the 60 mph standard shingles," says Eric Stafford, engineer for the Federal Alliance for Safe Homes, a nonprofit organization based in Tallahassee, Fla.

The high-wind shingles can be up to 50 percent more costly and require more labor to install, according to the NAHB Research Center's ToolBase Services. However, these shingles often come with 30- to 50-year limited product warranties and 10-year coverage against algae growth. Homeowners in certain areas may also be able to recoup some of the costs through discounts from insurance companies.

Remodelers should also consider replacing some or all of the roof sheathing; FEMA recommends using 5/8-inch plywood as the best option for wind resistance. While traditional fastening patterns spaced no more than 6 inches apart on center-of-roof framing members are acceptable, using ring shank nails instead of common roofing nails can provide greater wind resistance. Ring shank nails are recommended in hurricane-prone areas that see winds up to 110 mph.

Stafford suggests that remodelers in areas with high winds consider using hurricane ties as well. "[FLASH] has a course specifically on retrofitting the roof," he says. "We recommend implementing some wind-resistant technologies, such as attaching hurricane ties to make sure your roof stays in place."

The ties - also called clips or straps - are metal fasteners mounted between the roof and the main house structure. They reduce the likelihood of dangerous wind uplifts that can completely rip the roof off a home during a hurricane or tornado. Ties are significantly more secure than traditional toe nails, which are driven at an angle from the top of a wall into a roof truss or rafter.

"The wind wants to pull the roof off the building," Stafford says, "and those toe nails don't give you as much resistance as metal connectors that wrap around the rafters and then fasten to the wall."

Further preventive measures should be taken when the home has a gabled roof, according to the Institute for Business & Home Safety, a Tampa, Fla.-based nonprofit organization. IBHS warns that the end walls of gabled homes are subject to considerable pressure in high-wind storms.

"The intersection of that gable-end framing or gable-end truss and the wall is particularly vulnerable to wind forces and will fail in severe storms," Stafford says. "In fact, one of the most consistent failures in Hurricane Andrew in 1992 were gabled-end walls." He notes that this pattern was also observed in the 2004 hurricanes.

Bracing for the worst

Fortunately, bracing gable end walls is not particularly difficult. Since the end trusses normally attach to the top of the walls, IBHS recommends securely nailing the bottom of the truss to the top of the wall and to adjacent trusses. This simple bracing measure will prevent the wind from shifting the gable end at its key connection point.

The benefits of bracing are not limited to gable end walls. Simply by connecting wall- and floorboards with properly rated (rating requirements depend on the type of framing and the location) plywood or oriented strand board, the walls are more likely to remain square in high winds and resist excessive racking, or shifting of the frame on its foundation.

FEMA also recommends tying structural frames to foundations with properly sized anchor bolts. In concrete block foundations, anchor bolts should go a minimum of 15 inches into the foundation. This ensures that the bolt reaches the second course of foundation blocks and that bolts will hold during strong winds.

Similarly, the proper nailing schedule - the size, type, and placement of nails - for sheathing and shingling can make an enormous difference. During Hurricane Andrew, widespread damage to roof sheathing was blamed on improper nailing, particularly in older buildings.

Studies of Hurricane Andrew by the NAHB Research Center indicate that nail edge distance tolerance is quite tight, with an acceptable distance from 1/4 to 3/4 inches. However, nail overdrive - when a nail penetrates too far - can actually reduce uplift strength of the connection.

Simple measures

Because of its width, a garage door is one of the weakest points of a home. In high winds, it can shake and even be forced out of its tracks. When this happens, the house is exposed to the full force of the winds and potentially catastrophic damage. Replacing or reinforcing the garage door will improve wind resistance.

Installing vertical bracing into the weakest points of each panel will reinforce a garage door. However, in high-wind areas it may be more practical to install a wind-resistant one with a properly reinforced track, says IBHS vice president of engineering Tim Reinhold. "The garage door needs to be a system that has been properly tested for those types of high winds," he says.

One of the other greatest dangers in tornados and hurricanes is wind-borne debris. Impact-resistant doors and windows can reduce the likelihood of interior wind and water damage, while the proper shutters can provide another layer of protection.

"There are a lot of shutters on the market," Stafford says. "The shutters that [FLASH] recommends have to pass a series of tests on hurricane resistance. One of the biggest things they have to be able to do is resist the passage of a 2-foot by 4-foot cut of wood flying at 35 mph."

Finding what works

"With each major weather event, investigations serve to focus attention on specific performance issues. By working with the industry, PATH addresses those issues and identifies solutions," says Dana Bres, a research engineer with HUD and PATH.

In time, actuarial data will provide new clues as how to best fortify homes against storms. For now, a focus on material durability and attention to details - such as lapping wall top plates at intersections with interior walls and attaching sheathing to a common stud - will give homes a much better chance of weathering high winds.

 


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