Foundation types

Slabs, crawl spaces, basements and how each one fails.

• How are manufactured homes set on piers in Oklahoma?They rest on a steel chassis carried by concrete-block piers on small pads, held by anchors. Shallow pads ride up and down as Oklahoma clay swells and shrinks.
• How do slab-on-grade foundations move on Oklahoma clay?The slab moves as clay under its edges or center gains or loses moisture, and the shape of that movement decides which repair, if any, fits.
• How does a pier and beam crawl space foundation work?The house sits on a raised wood floor over a crawl space, with a perimeter footing and wall and interior piers carrying beams and joists.
• What are stem wall and grade beam foundations?A stem wall is a short wall on a continuous footing. A grade beam spans drilled piers set below swelling clay, with a gap under it so clay cannot lift it.
• What is a post-tensioned slab and does it move on Oklahoma clay?A PT slab is reinforced with steel tendons pulled tight after pouring; used on expansive clay, it still moves when clay swells or shrinks unevenly.
• Why do driveways, patios and sidewalks move in Oklahoma?Flatwork is thin, lightly loaded and sits on the soil, so swelling clay lifts it and drying or washed-out soil lets it drop more readily than the house.
• Why do Oklahoma basement walls crack and bow?Most trouble comes from sideways pressure: clay that swells when wet and water that builds up in the backfill behind the wall.