A long standing tornado myth states that if you open windows during a tornado, it will prevent the roof from being blown off. There’s another myth that says you should only open north facing windows. I’m not sure where these myths originated, but they are both pretty silly. It’s really a matter of simple physics.
The roof on well constructed houses are held together by steel “L” brackets, a lot of nails, and 2×4 wood trusses. A window is nothing more than about a 1/4 inch pane of glass. If this myth were true, in that a closed window could be responsible for causing the roof to blow off, that is saying the glass is stronger than the construction of the roof. This simply isn’t true.
If a tornado’s winds are strong enough to hurl a car hundreds of feet through the air, and scour asphalt off the road, then your windows being open or closed won’t make the slightest bit of difference. The other argument that opening the windows on one side of the house and not the other might cause more internal air pressure is also false. The same principal applies. The glass window will give out and break far before the roof or walls do. Despite what some think, the air pressure differential or “sucking” of the tornado doesn’t cause a house to explode. It’s the brute force strength of the wind, which can reach speeds in excess of 250 mph.
The air pressure differential between the inside of your home and inside of a tornado is not that great. The Texas Tech’s Institute for Disaster Research conducted several experiments and concluded that the pressure drop found inside a tornado with a wind speed of 260 mph was only about 10%. That’s about 1.4 pounds per square inch, which really isn’t that much. Most well built houses and buildings can vent this great a pressure change with no ill affects on the dwelling. Even if all the windows and doors are closed. There are attic openings, chimneys, furnace vents, and other small openings underneath doors and closed windows where air can escape. It’s not the pressure differential that destroys a house when a tornado hits, even though it may look like the house is exploding.
There are two things associated with tornadoes that can destroy a house. First and foremost, the wind. A wind clocked at 260 mph is going to flatten just about everything in its path regardless of the windows being open or closed. The broadside of a house is going to act like a sail and a 4’x4′ window sized hole isn’t going to matter. Second, wood beams, trees, large debris, and a million bricks from your neighbors house will become airborne missiles. So again, opening the windows during a tornado isn’t going to minimize the damage to your house one single bit.
The best thing you can do is save the time you would wasted opening the windows by seeking shelter sooner. Watch the news if there is the threat of severe weather. If a tornado is heading your direction and you cannot escape, the safest place to be is below ground in a storm shelter or basement. The the next best places are either in an interior closet on the first floor, or a bathtub. If you see the tornado, do not try to outrun it in your car.