As someone who has never lived in — let alone set foot in — the supercell-friendly plains region between the Rocky and Appalachian Mountains colloquially referred to as Tornado Alley, I always just assumed that an overwhelming majority of homes in the area have basements and storm cellars. You know, somewhere safe where Em, Henry, and the farmhands can scramble to when things start to get hairy outside.

In reality, underground storm shelters are somewhat of a rarity in Oklahoma, the country's third most active tornado belt state, with only 3.5 percent of homes in the greater Oklahoma City metropolitan area having basements and conventional storm cellars, according to Reuters. Included in this figure is the city of Moore, which was pummeled by a violent EF5 tornado that tore through the region earlier this week, claiming at least 24 lives and leveling thousands of homes. Speaking to CNN, Mike Hancock, president of Edmond, Okla.-based Basement Contractors, estimates that "probably less than one tenth of one percent" of homes built in Moore have basements.

And as Moore begins the painful process of digging out, Mayor Glenn Lewis is already vowing to enact an ordinance that would require all newly built single- and multi-family homes in his ravaged city to include an underground storm shelter and/or aboveground safe room. “We’ll try to get it passed as soon as I can,” Lewis told CNN. This is the second time that Moore has been hit by an EF5 tornando, the first being in 1999.

So why then, in a populous, suburban sprawl-heavy region that’s been repeatedly walloped by devastating tornados, are underground storm shelters in private homes not compulsory? The answer is a bit complicated, but boils down to two things: Red clay and red state attitudes.

As explained by The Atlantic’s Megan Garber. the porous, red clay-based soil found in much of Oklahoma isn’t exactly conducive to basement-building:

Here's the problem with that when it comes to building basements and underground shelters: Clay is particularly fickle as a foundation for construction. When loamy soils absorb rainwater, they expand. And when the weather's dry, they contract. This inevitable and yet largely unpredictable variability makes basement-building a particular challenge, since it makes it nearly impossible to establish firm foundations for underground construction.

And while above-ground homes can be built on these somewhat shaky foundations, adding the element of open space in the form of a basement is a nearly impossible feat of engineering. There is a chance your house, its basement surrounded by glorified mud, will eventually simply topple into itself.

To mitigate this, contractors have been experimenting with steel reinforcements for basements, bolstering underground walls with steel beams that are drilled directly into the bedrock below. The problem here, though, is that much of Oklahoma's bedrock is composed of limestone, which, just like the soil above it, absorbs water. And which, when it's sapped of moisture, becomes chalky. 

So, you can try to enforce your basement with steel; ultimately, though, the steel will be anchored to rock that is 'rock' only in the broadest sense of the word. 

Garber goes on to note that constructing an adequate, steel-reinforced underground shelter or storm-resistant basement capable of withstanding an EF5 tornado like the one that razed much of Moore isn’t cheap in the least: Most projects cost, at a minimum, thousands of dollars. Mayor Lewis even admits that “anybody that lives in any tornado area should have (a storm shelter), but it's just the matter of cost."

Aboveground safe rooms are often cost-prohibitive as well, according to NBC News:

But building a steel room on a concrete slab adds thousands to the price of a new home in a market where a typical property is worth $108,000. And for homeowners, spending $2,500 and up to add tornado protection to existing homes often isn’t feasible without assistance in a state where the median income is $44,000 — $8,000 below the national figure.
When it comes to entire tornado-proof homes, they’re not totally impossible to construct. However, most homeowners would find that installing missile-resistant doors capable of deflecting projectiles being hurled through the air at 250 miles per hour to be a touch on the spendy side (save for this guy) and the overall costs of building a tornado-proof home completely unfeasible.

And as mentioned, politics play a role in the dearth of storm shelters in Oklahoma along with prohibitive costs and uncooperative geology. Having introduced several failed bills to the state Legislature that would require safe room and shelter construction in homes, state Rep. Richard Morrissette. D-Oklahoma City, explains to NBC News: “This is a red state. People don’t like anything that is mandated. They don’t like it when the government says they have to do something.”

Like Oklahoma, fellow tornado belt states Kansas and Missouri are without ordinances or building codes that require private homes to have storm shelters. Following a deadly tornado that struck the town of Enterprise, Ala., in 2007, that state now requires all schools  to include a safe room. After singling out soil as "the reason we don't have basements," the National Storm Shelter Association's former president, Tom Bennett, admits to NBC News that "Oklahoma may be headed in the direction of Alabama."

Via [NBC News], [The Atlantic]

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

Gimme shelter: Why storm cellars and basements are a rarity in Oklahoma
There's a dearth of homes with storm shelters in and around tornado-prone Oklahoma City due in part to soil conditions, costs and red state attitudes.