Prevent Tornado Damage
By: Amanda Campbell
Updated: August 30, 2010
Michael Holigan taped a segment recently about a tornado that had ravaged a nearby neighborhood a couple weeks earlier. The tornado tore that neighborhood apart in less than 20 seconds. The people living there had no warning whatsoever, not even a minute to prepare. What would you do? Would you know where to go? Do you know what you can do to your house right now to resist the kind of damage we saw around us? There's no way you can completely prevent the destructive forces of nature from damaging your house, but there are a lot of things you can do to minimize the damage that a storm of this magnitude can cause.
Consider safety issues when building a house. There are a number of simple and relatively inexpensive building tools & practices (anchor bolts, corners wrapped in OSB, wind-resistant garage doors & rafter clips) that help tie a house together, foundation to roof. We'll describe each of these for you in detail. The result is greater structural integrity & greater resistance to the kinds of extreme weather conditions we saw everywhere around us. The tornado ripped dozens of houses apart.
Tornados create an immense negative pressure that makes houses literally "explode" outward. Tornadic winds can easily lift roofs off frames. Holes in the roofs leave interiors totally exposed to the elements. The system of safety features we'll describe to you might have prevented some of the tornado damage we witnessed.
Michael took us through a cul-de-sac where the tornado swept some foundations clean of any evidence of a structure. Anchor bolts can help the frame of a house resist these forces. Anchor bolts are L-shaped bolts that are placed in a foundation just after the concrete is poured, while it's still wet. Once the concrete sets, these bolts are anchored in place. They stick out an inch or two above the foundation. Framers build the walls and drill holes in the base plates (the bottom piece of wood on the exterior walls). The entire wall is then lifted in place & lowered onto the bolts, then secured to the foundation with washers and nuts. This creates a much stronger structure than simply nailing base plates into the foundation, a practice many builders still follow. If a wall is simply nailed into a foundation, a strong wind could place a tilting force on the wall and loosen the nails holding it to the foundation like a claw on a hammer can loosen nails.
Experts recommend 2x6 studs as the main structural elements in the walls of a solid frame. 2x6s cost more to a homebuilder up front than smaller 2x4s, but since 2x6s are larger structural members, they contribute to an overall increase in the strength & stability of the frame compared to 2x4s.
Consumer Tip - 2x6s may cost more up front, but since they allow room for more and better insulation, they'll quickly pay for themselves in lower energy bills.
Once the four walls of the frame are built, the next step is bolstering the strength of the corners of the frame. This is done using sheets of Oriented Strand Board (OSB). OSB is an engineered wood product made of narrow strands of wood fiber that are oriented lengthwise and crosswise, then bound in resin for increased strength. The corners of the frame are "wrapped" in OSB, top to bottom, and extending out at least four feet from the corners. The "box" of the frame can now resist shearing and twisting forces better than it can without the reinforcement at the corners. In our segment, Michael held a common cardboard box that he twisted with his hands to demonstrate the racking or twisting forces on a frame that wrapped corners counteract and resist.
Wrapping corners in OSB is a minimum safety step. Michael strongly recommends you wrap your entire frame in OSB, so your house is solid like a tank against the attack of severe wind & weather.
We saw roofs missing everywhere. We saw nails sticking out of most of the rooflines showing where roof rafters used to be nailed in. Rafters are the parallel beams that support the roof above the top floor of the house. Most walls are designed simply to handle the weight of the roof above them - that's a gravitational load in a downward direction. Strong winds can get under the eaves of a roof and exert an upward load that could easily lift the roof off the frame. If a roof is simply nailed to the top of the walls, the wind can pull those nails out like the claw of a hammer can pull nails out of wood.
Hurricane Straps or Rafter Clips form a stronger connection between the walls and the roof to resist those forces. Rafter clips are simply pieces of metal that screw into the top of a wall stud and the bottom of a rafter, where the rafter and wall stud meet. These clips strengthen the connection between wall and roof to withstand three times the wind force of a frame without rafter clips. That increase in strength can literally mean the difference between experiencing minimal roof damage and suffering the total loss of your roof.
Consumer tip - Rafter clips cost about 50 cents apiece. The average 2500 square foot home may need a total of $100 worth of rafter clips. Measure that cost against the cost of roof replacement or repair after a severe storm.
The garage is very often the first part of the exterior to surrender to a tornado. Michael pointed out a couple of homes where a lot of the damage was worse in & around the garage. Even to the untrained eye, it was obvious that strong winds blew through the garage doors first, then funneled through the garage as a point of entry to wreak havoc on the rest of the house. On some houses, the garage roof & garage doors were blown completely away, while the roof over the rest of the house suffered minimal damage. Damage radiated outward from the garage area on a number of homes.
A number of manufacturers now build garage doors specifically designed to resist severe wind forces. They look and operate just like normal garage doors. The garage door hinges have springs that go into tension when a strong wind tries to push a door in. That tension counteracts the wind force and tends to push the door back into place, strengthening the most vulnerable point of entry on the exterior of your house. All these features form a cohesive and unified system to strengthen the entire frame of your house. Anchor bolts secure the walls to the foundation. OSB wrapped around the corners ties the entire wall to the base plate, which is anchored to the foundation. Hurricane straps anchor the roof to the walls, completing the system top to bottom. Fortified garage doors strengthen the weakest point of resistance on the exterior. All the individual features work together to fortify the frame against destructive forces.
Some policies may reward a homebuilder who incorporates safety devices like anchor bolts & rafter clips with reduced rates. Most people unfortunately don't learn about their mistakes until they file a claim after a storm like this and find out they don't have the coverage they thought they did. For instance, you may buy insurance for a certain amount of coverage based on the purchase price of your home, but you may never tell the insurance company about improvements you make that add value to your house. Sometimes home prices shoot up in a neighborhood & that increased value isn't reflected in the coverage unless you call the insurance company to update your policy.
We met a homeowner who could not rebuild his house as it stood because his policy was undervalued. Beware of predatory contractors who follow storms and offer quick fixes to survivors, only to do shoddy work or skip town without doing work you've already paid for in advance. The insurance companies cannot reimburse you again to compensate for this criminal activity once they've paid money for a repair. So the lesson is - make sure you get repair work done by a reputable and locally known contractor.
The neighborhood we visited is no different from yours or mine. The people who lived through this tornado are no different from you or me. They've spent their lives watching disasters happen to other people on TV, and suddenly the disaster became real for them. This same thing could happen to you at any time, with absolutely no warning. Now's the time to do what you can to beef up the strength and integrity of your house. Chances are, most of you won't ever have to face the kinds of weather extremes that tore this neighborhood apart, but why take chances? A minor initial investment now (about $2000 on an average house for all the safety features we've described) could mean the difference later between survival & catastrophe.
Luckily, everyone survived in the neighborhood we visited, but you can't count on luck alone when you're facing the kinds of severe forces that did so much damage. Make sure everyone in your family knows exactly what to do and where to go in your house if bad weather hits without warning, like it did here. Go find the paperwork for your insurance policy right now and make sure you're adequately covered for the value of your house now, not when you bought it or built it. It's never too early to think about safety when you're building your new house.
Consider safety issues when building a house. There are a number of simple and relatively inexpensive building tools & practices (anchor bolts, corners wrapped in OSB, wind-resistant garage doors & rafter clips) that help tie a house together, foundation to roof. We'll describe each of these for you in detail. The result is greater structural integrity & greater resistance to the kinds of extreme weather conditions we saw everywhere around us. The tornado ripped dozens of houses apart.
Tornados create an immense negative pressure that makes houses literally "explode" outward. Tornadic winds can easily lift roofs off frames. Holes in the roofs leave interiors totally exposed to the elements. The system of safety features we'll describe to you might have prevented some of the tornado damage we witnessed.
Michael took us through a cul-de-sac where the tornado swept some foundations clean of any evidence of a structure. Anchor bolts can help the frame of a house resist these forces. Anchor bolts are L-shaped bolts that are placed in a foundation just after the concrete is poured, while it's still wet. Once the concrete sets, these bolts are anchored in place. They stick out an inch or two above the foundation. Framers build the walls and drill holes in the base plates (the bottom piece of wood on the exterior walls). The entire wall is then lifted in place & lowered onto the bolts, then secured to the foundation with washers and nuts. This creates a much stronger structure than simply nailing base plates into the foundation, a practice many builders still follow. If a wall is simply nailed into a foundation, a strong wind could place a tilting force on the wall and loosen the nails holding it to the foundation like a claw on a hammer can loosen nails.
Experts recommend 2x6 studs as the main structural elements in the walls of a solid frame. 2x6s cost more to a homebuilder up front than smaller 2x4s, but since 2x6s are larger structural members, they contribute to an overall increase in the strength & stability of the frame compared to 2x4s.
Consumer Tip - 2x6s may cost more up front, but since they allow room for more and better insulation, they'll quickly pay for themselves in lower energy bills.
Once the four walls of the frame are built, the next step is bolstering the strength of the corners of the frame. This is done using sheets of Oriented Strand Board (OSB). OSB is an engineered wood product made of narrow strands of wood fiber that are oriented lengthwise and crosswise, then bound in resin for increased strength. The corners of the frame are "wrapped" in OSB, top to bottom, and extending out at least four feet from the corners. The "box" of the frame can now resist shearing and twisting forces better than it can without the reinforcement at the corners. In our segment, Michael held a common cardboard box that he twisted with his hands to demonstrate the racking or twisting forces on a frame that wrapped corners counteract and resist.
Wrapping corners in OSB is a minimum safety step. Michael strongly recommends you wrap your entire frame in OSB, so your house is solid like a tank against the attack of severe wind & weather.
We saw roofs missing everywhere. We saw nails sticking out of most of the rooflines showing where roof rafters used to be nailed in. Rafters are the parallel beams that support the roof above the top floor of the house. Most walls are designed simply to handle the weight of the roof above them - that's a gravitational load in a downward direction. Strong winds can get under the eaves of a roof and exert an upward load that could easily lift the roof off the frame. If a roof is simply nailed to the top of the walls, the wind can pull those nails out like the claw of a hammer can pull nails out of wood.
Hurricane Straps or Rafter Clips form a stronger connection between the walls and the roof to resist those forces. Rafter clips are simply pieces of metal that screw into the top of a wall stud and the bottom of a rafter, where the rafter and wall stud meet. These clips strengthen the connection between wall and roof to withstand three times the wind force of a frame without rafter clips. That increase in strength can literally mean the difference between experiencing minimal roof damage and suffering the total loss of your roof.
Consumer tip - Rafter clips cost about 50 cents apiece. The average 2500 square foot home may need a total of $100 worth of rafter clips. Measure that cost against the cost of roof replacement or repair after a severe storm.
The garage is very often the first part of the exterior to surrender to a tornado. Michael pointed out a couple of homes where a lot of the damage was worse in & around the garage. Even to the untrained eye, it was obvious that strong winds blew through the garage doors first, then funneled through the garage as a point of entry to wreak havoc on the rest of the house. On some houses, the garage roof & garage doors were blown completely away, while the roof over the rest of the house suffered minimal damage. Damage radiated outward from the garage area on a number of homes.
A number of manufacturers now build garage doors specifically designed to resist severe wind forces. They look and operate just like normal garage doors. The garage door hinges have springs that go into tension when a strong wind tries to push a door in. That tension counteracts the wind force and tends to push the door back into place, strengthening the most vulnerable point of entry on the exterior of your house. All these features form a cohesive and unified system to strengthen the entire frame of your house. Anchor bolts secure the walls to the foundation. OSB wrapped around the corners ties the entire wall to the base plate, which is anchored to the foundation. Hurricane straps anchor the roof to the walls, completing the system top to bottom. Fortified garage doors strengthen the weakest point of resistance on the exterior. All the individual features work together to fortify the frame against destructive forces.
Some policies may reward a homebuilder who incorporates safety devices like anchor bolts & rafter clips with reduced rates. Most people unfortunately don't learn about their mistakes until they file a claim after a storm like this and find out they don't have the coverage they thought they did. For instance, you may buy insurance for a certain amount of coverage based on the purchase price of your home, but you may never tell the insurance company about improvements you make that add value to your house. Sometimes home prices shoot up in a neighborhood & that increased value isn't reflected in the coverage unless you call the insurance company to update your policy.
We met a homeowner who could not rebuild his house as it stood because his policy was undervalued. Beware of predatory contractors who follow storms and offer quick fixes to survivors, only to do shoddy work or skip town without doing work you've already paid for in advance. The insurance companies cannot reimburse you again to compensate for this criminal activity once they've paid money for a repair. So the lesson is - make sure you get repair work done by a reputable and locally known contractor.
The neighborhood we visited is no different from yours or mine. The people who lived through this tornado are no different from you or me. They've spent their lives watching disasters happen to other people on TV, and suddenly the disaster became real for them. This same thing could happen to you at any time, with absolutely no warning. Now's the time to do what you can to beef up the strength and integrity of your house. Chances are, most of you won't ever have to face the kinds of weather extremes that tore this neighborhood apart, but why take chances? A minor initial investment now (about $2000 on an average house for all the safety features we've described) could mean the difference later between survival & catastrophe.
Luckily, everyone survived in the neighborhood we visited, but you can't count on luck alone when you're facing the kinds of severe forces that did so much damage. Make sure everyone in your family knows exactly what to do and where to go in your house if bad weather hits without warning, like it did here. Go find the paperwork for your insurance policy right now and make sure you're adequately covered for the value of your house now, not when you bought it or built it. It's never too early to think about safety when you're building your new house.
