With respect to freezing and foundations, Texas can be divided into two areas: anyplace where the ground will freeze to a depth below six inches, and the rest of the state.  Generally, the only places where the ground will freeze are west Texas and the panhandle. 

If you have a slab on grade foundation, your pipes will be more than six inches below ground.  Heat from the ground and from the house will keep the temperature of the soils under the foundation above freezing.  You do not need to worry about freezes affecting your underground pipes.  At the same time, the edge of your foundation will almost always be at 12 inches into the ground.  As a result, the freeze will not get below your foundation and freezing soils will not be able to push up on your foundation.

Pier and beam foundations, homes with a space between the floor and the ground (the crawlspace), can have problems.  If a crawlspace is open to the cold air, pipes in a crawlspace can freeze.  If waterlines freeze and burst, water can flood a crawlspace.  In extreme cases, the flooding can cause foundation movement.  Of course, when pipes break, the immediate problem of repairing the breaks gets attention first.

The best way to protect a crawlspace and the pipes in it from freezing is to cover the vents.  Vents are openings in the sides of the wall that forms the edge of the foundation.  The vents allow air to circulate and help to control humidity.  Once the vents are covered, heat from the ground and from the house will be trapped in the crawlspace and pipes will not freeze.  It is also a good idea to let water drip from your faucets.  Dripping faucets will keep water flowing in your pipes and will help prevent freezing.

If you have pipes in your attic, it is very important to keep the temperature in the attic above freezing.  When hard freezes occur in southern Texas and along the gulf coast, there are always burst pipes in attics.