STORM-PROOFING YOUR HOME II

Michael Holigan: This is what was left of the little town of Jarrell, Texas after a tornado hit last May. Many of the houses were scraped clean off their foundations. On other houses roofs were lifted right off and walls collapsed. But scientists are looking at ways to make houses hold together better. Dr. Ernst Keisling of the Wind Research Center at Texas Tech University studies what happens when a heavy wind hits a house. When a typical tornado hits a home why is it the home almost looks like it explodes?

Ernst Keisling: Good question and the thought for many, many years was that it did literally explode due to external...or due to changes in pressure. But the fact is, even with a straight wind blowing, say, from this direction, the force would be inward on this wall, but on the roof overall the force is upward and one of the highest pressures occurs right in the downwind side of the roof at this point and tends to lift the roof off. Then on the two sidewalls the force is outward and on this leeward wall the force is outward. So, if we look at just a straight wind blowing over this house on four of the five exposed surfaces the forces are outward, on only the windward wall is the force inward.

MH: So, it's sort of like air hitting the airplane wing. It's going faster around the surface.

EK: Same basic phenomenon. And it's even heightened or worsened if, say, a garage door blows in or a window blows in on the windward side. Then you have a slight ballooning effect which adds an internal pressure to the outward forces which are already there.

MH: When the wind hits the house from the front and flying debris shatters a window or blows down a garage door, the wind gets inside the house and the pressure goes outward and upward. This stresses the back and sidewalls and pushes up on the roof. If the wind is strong enough something has to give and the house appears to literally explode. One of the things you can do to help protect your home in a high wind situation is reinforce all openings. That includes front doors and back doors, garage doors, and even your window openings. We're about to test a new type of window right now. The window isn't glass. It's called Paltech, a polycarbonate plastic coated with a special film. The manufacturer says it's shatterproof and even bullet resistant. So we hit it with a board at 50 miles an hour. The board bounced off and almost broke our camera, so we went around to the other side to film and upped the speed to 65 miles an hour. The force knocked the frame out of the holder, but the window stayed intact, exceeding the toughest standards for hurricane resistance. And what are researchers doing to improve strength of the structure of the house itself?

EK: Our attempts to improve structural performance focus on improving the connections to hold that shell or that envelope together to prevent that massive kind of damage.

MH: So bolting the frame down, the hurricane straps, proper corner bracing, anything we can do to keep the envelope together.

EK: Exactly.

MH: So the key thing in making your house stronger is to strengthen the connections that hold the envelope of the house together. There are several things you can do during the framing stage that are inexpensive, but make all the difference in how well your house will stand up during a strong storm. First, have your builder anchor the base plate of the frame to the foundation with bolts. The base plate is the bottom piece of wood on the exterior wall. The bolts should be put in place when the foundation is poured. Some builders just nail the base plate to the foundation, but in a high wind the wall can tip over and pull the nails out of the foundation, just like the handle of claw hammer pullings nails out of wood. To make the frame stronger, holes are drilled in the base plate then the whole wall is then set over the top of the bolts and a washer and nut are fastened down on the bolt. Next, the house needs to be cornerbraced, wrapped from top to bottom in solid sheets of oriented strand board, also called OSB or plywood. The corner bracing should extend out four feet from the corner in both directions. If you do this the whole wall is anchored to the base plate, which is anchored to the foundation. Finally, the rafter needs to be anchored. Many builders just toenail the rafter in place. That's just taking nails and driving them in at an angle. Not much support. And if a wind ever gets inside your home it just lifts the nails straight out of the wood. A great anchor for the rafter is a rafter clip, sometimes called a hurricane clip. You just nail those in place to the top of the wall and to your rafter. This will help hold your roof on in a high wind. And the cost? First, the bolts. All the bolts you need to anchor your walls to the foundation would cost less than $20.00 for the average house. For the corner bracing, OSB should cost less than $300.00 for the average home. And finally, the rafter clips. The average cost for the whole home is less than $50.00. It's sad to say, but most builders don't include these features in their standard homes. So if you want them, you'll probably have to ask for them. So at least for now, if you want a stronger house it's up to you to make it happen.

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Episode 58 1997 - 98 Season

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