Wind is the most common and most costly cause of damage to homes and other “light frame structures” in the United States. The 75-mile-per-hour-plus winds experienced in hurricanes put tremendous pressure on the roof, walls and foundation, and windblown debris can significantly increase the damage.
Although some measures, such as trimming trees and making sure your yard is clear of objects that could become flying debris, are things you can do right before a storm to protect your home, LSU AgCenter disaster recovery and mitigation specialist Pat Skinner says homeowners can do other things for more long-term protection.
“Studies completed following hurricanes show that typical light frame structures (stick-built homes) have some weak spots,” Skinner said. “By strengthening these crucial points, you can make your house much safer against wind.”
Among the points of where traditional frame houses are most likely to fail are the roof, exterior doors and windows, garage doors and connections between the wall and the roof and the wall and the foundation.
According to Skinner, two types of roofs are common in light frame structures. Those are gabled roofs and hipped roofs. A gabled roof looks like an “A” on the ends, and a hipped roof slopes upward and toward the ridge from all sides of the structure.
Gabled roofs are more vulnerable to wind force. Most gable ends are simple triangular frames set on top of the wall, forming a joint at the level of the ceiling. This joint typically has very little support.
“The gable end wall is pushed and pulled by wind forces and may be pulled completely out of the building if not properly braced,” Skinner explained, adding, “A failed gable end wall causes extensive damage to the structure – allowing the water and wind to go inside.”
Fortunately, installing braces inside the attic can provide the strength necessary to keep the gable end wall in place during hurricanes.
Bracing involves tying several rafters together, tying several ceiling joists together and adding diagonal pieces to strengthen the top and bottom of the gable end. Rafters are tied together by installing 2-by-4 or 2-by-6 “strong backs” between them. A strong back is two pieces of lumber joined with the narrow edge of one piece nailed or screwed to the face of the other piece, and Skinner says ceiling joists can be joined in the same way.
“With these strong backs in place, the movement of the gable end is resisted by the combined strength of the set of braced rafters and joists, not just by the one rafter the gable end is attached to,” Skinner explained, adding that for rafters at the gable end, you should start about 18 inches from the roof ridge.
The gable end wall itself is braced by running 2-by-4s or 2-by-6s from the top of the gable to a ceiling joist that is the same distance from the gable end as the height of the gable. (If the gable is 10 feet high, above the ceiling, the brace point should be 10 feet in from the gable. This will require a board roughly 14 feet long. Then a second brace – of equal length – is run from the bottom of the gable, where it joins the wall framing, to the roof-rafter, forming an X with the first brace.
Exterior doors and windows
Stopping wind from entering your house is very important, Skinner said, even when that wind is not carrying rain.
“When high winds enter a home, they create an internal pressure that can contribute to the roof being pulled off the home,” she said. “All of the exterior doors and windows should be secured properly.”
Storm shutters are one way to secure the housing envelope. Shutters can be installed over all windows and doors that have glass.
“Shutters provide effective protection,” Skinner said, adding, “Several kinds of shutters and impact-resistant screens are available for homeowners. These include panels made of plywood or other materials, which can be bought for a minimal cost but must be stored when not in use. There also are operable impact-rated colonial and bahama shutters, shutters that roll up and down and shutters that close accordion style.”
Replacing windows and doors with impact-resistant units is another measure homeowners can take to protect their homes. These windows or doors may be more expensive than shutters, but they provide a natural-looking alternative and work when no one is home to install them or make sure they’re closed.
Securing garage doors is another step homeowners can take to protect their homes against wind damage. Garage doors, especially double-wide (two-car) doors, can be very dangerous during high winds. They can be pulled off their tracks as a result of wind pressure. So these doors need to be strengthened to withstand high winds, and the framing around the garage door needs to be “beefed up.”
“Commercial retrofit kits are available for garage doors,” Skinner said. “Installing horizontal braces to the panels, replacing existing hinges with stronger ones and checking the center and end support for wind loads will strengthen your garage door against wind.”
Because of the tremendous forces involved in a larger garage door, however, Skinner advises replacing the door with one that is hurricane-rated, if at all possible, and having it installed professionally.
Hurricane winds impose three types of forces on a building – uplift, lateral load and shear. Connections between the framing members (rafters and walls) and between the walls and foundation are important for keeping the house “plumb” and for appropriately transferring all the loads to the ground
“Hurricane straps, clips and anchors provide a very effective solution to this problem,” Skinner explained. “Homeowners can use straps to connect the roof rafters to the studs of exterior walls, as well as using them to connect wall studs to the bottom plate (the piece that sits on the slab, in a slab home). Anchors can be added to hold the bottom plate to the slab.
“For homes with a raised-floor foundation, straps can be used to hold the bottom plate or sill to the foundation framing and the framing to the piers or foundation wall,” she added. “Piers may be the weakest point, depending on their construction.”
Skinner said a block pier with reinforcing bars and concrete-filled cells, set on a continuous grade beam is ideal. If this is not achievable, efforts should be made to anchor the floor framing to the ground.
For more information on home construction and safety, visit www.lsuagcenter.com . You also can learn more about LaHouse, the LSU AgCenter’s Louisiana House – Home and Landscape Resource Center by visiting that site. The LaHouse resource center showcases hurricane-resistant construction, retrofits for homes and a variety of “green” and healthy features, and it’s slated to officially open July 15.
Posted on Tue, August 12, 2014
by LSU AgCenter