Why Don't Homes in Texas Have Basements?
Elevation Map of Texas
I've Always Wondered
My mother is a Texan, and I remember sheltering in an inner hallway of my grandparents' house while tornado sirens went off. It was pretty clear to me at the time that we were not safe if the house took a direct hit: the walls were too flimsy, and the easy-peel roof was right over our heads.
I have always wondered why homes in Texas don't have basements as emergency protection against tornadoes. Tornadoes churn across the surface and move quickly; they skip over ditches and holes.
After the April 2012 spate of tornadoes that hit Dallas suburbs — and the Dallas airport while my uncle was in it — I once again started wondering. Basements are the best way to shelter from tornadoes, and yet many parts of Tornado Alley don't have them.
I'm not an architect or a home builder, but I'm a compulsive researcher. So I've been scouring for trustworthy answers from actual builders and architects. I hope the answers I've found here are right, but since I'm not an expert, I'd welcome any real homebuilders from Texas double-checking me and leaving a note in the guestbook below.
1) The Frost Line
In the north, housing regulations require home foundations to be dug below the frost line, which may be 5 to 6 feet down. Builders must sink the pipes that far down so they won't freeze and break. At that point, one might as well build a basement. In the south, the frost line tends to be less than a foot, so digging down is an unnecessary expense.
2) Expansive Clay Soils of Texas Shrink and Swell
Texas was formerly under the Gulf of Mexico, and a lot of the eastern half of the state has what are called "expansive soils," a kind of clay that heaves and flexes and plays havoc even when houses are placed on slab foundations. These clays expand up to 30% when wet, and dry quickly. Texas homeowners are known to water their lawns on hot, dry days to try to prevent their foundations from cracking. The pressure exerted by these swelling soils can exert up to 15,000 pounds of pressure per square foot! (Source: "Soil Issues and Residential Construction in Texas" from this site.)
That makes it very difficult and expensive to engineer basements for Texas houses.
3) High Water Table in Eastern Half of State
Historically, the water table in half of Texas has been very close to the surface, because the state is not that high above sea level. In Houston, for example, you can strike water just ten feet down in many areas. Basements too near the water table are often flooded. Recent droughts have pushed the water table lower, but homebuilding construction has to account for ordinary and wet years, not just drought.
4) Limestone Bedrock Is Difficult to Dig
This may be an excuse rather than a valid reason, but there are widespread complaints about the limestone (old seabed) in central and western parts of the state making it hard to dig, even to plant trees in the back yard. Limestone is the same kind of rock that forms the Alps! In many parts of Texas, there's only a thin layer of dirt above limestone.
Limestone is softer than many kinds of rock, but it's still rock. So it costs more to excavate a basement in limestone than ordinary soil. It can be done, and some new upscale homes in the Austin area do have basements, but I suspect they're out of the price range of most Texans.