The frost line is the depth at which groundwater in the soil won’t freeze during the winter. So to avoid frozen pipes and the potential for breaks, home builders in northern states must sink their foundations (and the pipes) deeper into the soil to get below the frost line. And once you’ve dug that far down, you might was well put in a basement. However, in Texas the frost line may actually be less than a foot deep below the surface. This means digging any deeper is really an unnecessary expense.
If you paid attention during your Texas History 101 class, then you might remember that much of the Lone Star State was at one time covered by the Gulf of Mexico. And as the coastal waters receded, much of the state was left with “expansive soils”—consisting of clay formations that can heave and flex during the rainy season; exerting up to 15,000 pounds of pressure per square foot! (Source: “Soil Issues and Residential Construction in Texas”). These same soils may also contract and settle during the hot dry months of summer. In fact, it’s not uncommon to see homeowners in Texas actually watering the soil around their foundations to prevent them from cracking during a drought.
In terms of geology, the top layer of an underground formation (soils, rocks, etc.) that is permanently saturated with water is considered the Water Table. And much of the eastern half of Texas, as a result of being only a few feet above sea level, has a water table that is very close to the surface. For example, you can actually strike water just ten feet down in many areas around Houston. So basements sunk too near a high water table, often flood. Even though droughts have pushed the water table to lower depths in recent years across Texas, home builders and contractors must take into account all types of historic climate conditions (dry, wet and ordinary seasons).
Moving from the eastern side of Texas westward, you find another geologic formation that results in a lack of basement building…limestone. Although limestone is actually softer than many other types of rock, it is still rock. And excavating a hole into rock, deep enough to sustain the construction of a basement, will always be more costly than simply digging in dirt. Now don’t get me wrong. I’m not saying that digging out limestone can’t be done. In fact, some of the newest homes in the upscale areas around Austin (Lakeway) are being constructed with basements. However, the expense of rock blasting and removal usually puts the price range of these custom homes much higher than what the average Texan is willing to spend.