When tornado sirens are blaring, wondering where to seek shelter from the storm is the last thing you want to be thinking.
And while your home's basement is the safest place to be in a tornado, they weren't built as storm shelters.
Basements are very much a function of the region of the United States where the house is built, according to Rose Quint, the assistant vice president of survey research at the National Association of Home Builders.
"They are much more popular in the colder Northeast and West than in the warmer South and West," Quint said.
And building a basement in areas where it’s already necessary to dig deep to build foundations that will withstand freezing temperatures also makes economic sense.
"The digging has to happen by code," Quint said.
The International Residential Code, which forms the basis for most residential building codes adopted in the U.S., tabulates how thick a concrete or masonry basement wall needs to be and the amount of any steel reinforcing needed in the wall. The code also specifies measures to protect against groundwater or rainwater leaking into a basement.
"In Florida, the high level of the water table makes it impossible to have a basement," Quint said.
While a basement may provide some protection against weaker tornadoes, houses – and most buildings in general – aren’t designed to resist the most extreme wind speeds associated with tornadoes like the ones that struck Illinois and Kentucky late last year, according to Quint.
"Only a storm shelter or safe room specifically designed to resist tornadoes will keep occupants safe," Quint said. "A portion of a basement could be constructed to those standards if a homeowner desired, or prefabricated units that can be bolted to the concrete floor of a basement are available."
Most basements are reinforced concrete walls buried underground.
"This protects you from flying debris and also walls or roofs that may collapse. There have been several studies on where to go or what corner of the basement do you shelter in. Regardless, being underground is your safest bet," FOX Weather meteorologist Stephen McCloud said.
New homes in the South lack basements
There were 1,374 tornadoes in the U.S. last year, and about 10% of them were reported in Texas. Alabama and Mississippi were a close second and third with more than 200 combined.
When comparing new homes in the U.S. and across the four regions, the United States Census Bureau shows the share with a full or partial basement in 2020 was as high as 68% in the Northeast and as low as 6% in the South.
By code, Quint said, the footings of a house must extend at least 12 inches below the undisturbed ground surface or to the frost line – the depth to which the ground freezes in the winter.
"The frost line is much deeper in the colder Northeast and Midwest regions of the U.S. than in the warmer South and West, as much as 3 or 4 feet below the ground in some places," Quite said. "Once you are excavating down that far and removing that much soil, going down a few more feet to create a basement is cost-effective."
No such thing as guaranteed safety
While the most violent and rare EF-5 tornado can level and blow away almost any house, most tornadoes are much weaker and can be survived using some safety precautions.
There is no such thing as guaranteed safety inside a tornado, according to the National Oceanic and Atmospheric Administration's Storm Prediction Center.
In a house with a basement, NOAA recommends avoiding windows and finding a sturdy object to hide underneath, like a heavy table, or cover yourself with a mattress or sleeping bag.
You also want to avoid staying under any heavy objects that might be placed on the floor above you, like a refrigerator or furniture. A weakened floor might cause those items to crush you.
If you don't have a basement, an interior room of your home with no windows is the next place to go in the event of a tornado. Anyone living in a mobile home should get out and find a more stable structure where they can take shelter.