UPDATED 5/22/13 12:30 pm
The deadly tornadoes that struck outside Oklahoma City on Monday have a lot of people asking why there aren’t more storm cellars and safe rooms in the area, which would have enabled more residents to shelter safely.
Glenn Lewis, the mayor of devastated Moore, Oklahoma, said today that he wants to pass a law requiring either tornado shelters or safe rooms in new homes. “We’ll try to get it passed as soon as I can,” he told CNN.
In the meantime, however, why were so many area residents unable to flee into a conventional storm cellar or basement as the storm approached? To debunk one popular myth: It’s not that these structures can’t be built in the area. But a combination of market and climatological forces makes them expensive and rare.
A key factor behind the dearth of basements in Oklahoma is the region’s frost line. Structural foundations everywhere need to be set below the depth at which the surrounding ground freezes. In most northern states, that means digging as much as six feet down — and if you’ve already gone to that much effort, you might as well just go ahead and build a basement. In Oklahoma, however, the frost line is only about 18 inches below the earth’s surface, and since there’s no structural or financial advantage to digging deeper, most builders don’t. “The main issue is cost,” explains Calvin Taylor, owner of Taylor Concrete Construction in the northeast Oklahoma city of Tahlequah. “They can go down and put a slab floor down for less.”
Then there’s the unusual quality of the earth itself in parts of Oklahoma. In the northeast part of the state, rocky soil often requires builders to use a jackhammer to dig basement, which is more expensive than the conventional process. Other parts of the state have unusually shallow soil covering sandstone bedrock, which means even more heavy-duty excavation. That can add several hundred to a few thousand dollars onto the cost, says Mike Hancock, president of Basement Contractors Inc., in Edmond, another suburb of Oklahoma City. (Hancock, one of just a few builders in the state who specializes in basements, runs classes teaching other contractors how to construct basements that can withstand Oklahoma’s geology.)
None of these problems are insurmountable, Hancock says. You just need more steel reinforcing beams, more concrete, better drainage, and higher-quality waterproofing material if you want a dry, structurally sound basement in the area — and that all adds up to considerable additional expense. Constructing a new basement runs an average of around $60,000, which is about $10,000 more than it costs in other locations and three to four times as much as building a concrete slab foundation. And that doesn’t include the cost of wall framing, sheetrock, electrical wiring, and other niceties.
On top of all that, the market generally isn’t willing to pay extra for homes with storm cellars, despite the safety benefits. Taylor argues that a basement is a cheaper way to add square footage to a home than building a bigger house. But few buyers consider below-ground space as valuable as rooms in the rest of the house. Many appraisers don’t, either: Hancock says home buyers and sellers can run into trouble when they go to take out or refinance a mortgage because living space that’s “below grade,” in technical terms, is often written off as less valuable than above-ground square footage.
Storms like those that hit Monday often bring a renewed interest in basements and safe rooms, but the attention is usually short-lived, says Taylor: “A lot of people roll the dice and hope they’ll never see a tornado.”