Soil and drainage around Spring

North of Houston, the ground changes

The Handbook of Texas describes Harris County as level coastal prairie in its southern half, with the northern half reaching into the rolling East Texas timberlands. Its soil is heavy black coastal clay in the south and sandy loam north of Buffalo Bayou. The land rises from about 55 feet above sea level in the middle of the county to over 200 feet on its northern edge, where Spring Creek forms the county line.

Across Spring Creek, the Handbook describes Montgomery County, home to The Woodlands and Oak Ridge North, as flat to gently rolling Piney Woods country with loamy surface soils over deep, reddish, clayey subsoils.

The Texas Almanac notes that the Coast Prairie's soils are lighter-colored and sandier in a strip along its northwestern edge. Wikipedia's account of Tomball says the railroad stopped there because it sat on the boundary between the low hills and the flat coastal plain.

Loamy on top doesn't mean no clay

A sandy or loamy surface can sit over clay subsoil, and clay is what shrinks and swells with moisture. So soil type alone doesn't tell you whether your slab will move. You can see the mapped soil for your address, subsoil included, in the USDA's free Web Soil Survey.

Drainage you can control

The Texas Section ASCE repair guidelines include several steps that apply around any slab:

• Slope the ground away from the house at 5 percent or more for the first 10 feet. That's 6 inches of fall, by our arithmetic.
• Extend downspouts well beyond the foundation into areas that drain.
• Where subsurface drains are used, give them a continuous slope of at least 1 percent, and 2 percent where practical.
• Keep soil moisture fairly even around the house, without overwatering.

Trees

Montgomery County's Piney Woods put a lot of trees close to houses. The same guidelines warn that removing a large tree can let the soil swell as it regains moisture, and suggest pruning as a possible alternative. Talk to an engineer before you cut down a tree to fix a foundation.