These workmen are preparing to lay a post-tension foundation. It's a slab foundation that's engineered to withstand the movement of the expansive clay soil. First, sand is brought in to build a stable, level surface. Polyvinyl is then laid over the sand to provide a moisture barrier. Rebar is laid down in the corners to reinforce the concrete, but the real strength of this post-tension foundation will come from the cables being laid down inside the foundation. The cables rest on small platforms called "chairs" that will hold them in the center of the concrete as it's poured. The engineering of most foundation calls for pouring exactly 4 inches of concrete -- no more, and no less.

After the concrete has been allowed to harden and cure for a week or so, it's time to stress -- or put tension -- on the cables. Wedges are applied to one end of the cable to keep it from moving inside the foundation. Then a hydraulic ram pulls the other end with 55-hundred pounds of pressure. That results in 32- thousand pounds of force per square inch holding the foundation in place -- even if the ground shifts around it. Once they're stressed, the cables are cut off and mortared over, so most homeowners don't even know they're there. If you're building your new house on expansive clay soil, be sure to tell your builder you want a post-tension foundation.