Guide
Slab, post-tension slab or pier and beam: what your Texas house has
Updated
Texas built most of its post-war housing on concrete slabs poured directly on expansive clay. What you have under the floor decides what repair even looks like.
Telling them apart
- Slab on grade
- A single reinforced concrete slab poured on the ground with thickened perimeter and interior beams. No crawl space, no floor vents around the outside of the house, plumbing runs under or through the slab. The default for Texas homes from the 1960s onward.
- Post-tension slab
- A slab on grade with steel tendons run through it and tensioned after the pour. Common in newer Texas subdivisions. Look for small capped or patched circles in a grid around the slab edge, and for a warning plate or stamp near the garage. Nothing may be cut, cored or drilled into a post-tension slab until the tendons have been located: cutting one is dangerous and expensive.
- Pier and beam
- Timber floor structure on beams carried by piers, with a crawl space underneath. You will usually see foundation vents around the perimeter and a crawl space access hatch. Common in older Texas housing stock and in areas where slabs were never the norm.
Why the type changes the repair
- Slab on grade is repaired by installing piers under the perimeter and, where needed, interior beams, then lifting or stabilizing. Interior access means breaking the slab or tunneling.
- Post-tension slabs are repaired the same way at the perimeter, but any interior work needs the tendon layout established first. Expect scanning, and expect a contractor who shrugs at this to be the wrong contractor.
- Pier and beam is often cheaper and less disruptive to correct, because the crew can work in the crawl space: shimming, replacing rotten sill or beam sections, adding or re-supporting interior piers. It brings its own problems, moisture, ventilation, rot and pests under the floor.
- Plumbing sits differently. Under a slab, a leak is invisible and expensive to find. Under a pier and beam house, it is usually visible from the crawl space, which is a genuine advantage.
Which cracks matter
TREC's guidance for Texas inspectors lists the visible indications used to judge foundation performance: doors that bind, do not latch or are out of square, framing or frieze board separations, sloping floors, cracks or separations in walls, ceilings or floors, and buckling or cracking of masonry cladding (TREC). The same guidance draws the distinction that matters most:
- Uniform settlement
- The whole foundation settles evenly. TREC describes this as generally not harmful, maintaining structural stability.
- Differential settlement
- One part settles more than another. This is the uneven movement that leads to cracks, misalignment and structural damage, and it is what repair is trying to correct.
TREC also notes that some movement over time is normal, particularly in areas like Texas where clay soils dominate, because clay expands and contracts with soil moisture. A hairline crack that opens in August and closes in December is telling you about the weather. A stair-step crack in brick that gets wider every year is telling you about the foundation.
What causes the movement
The causes TREC lists are the same ones a Texas engineer will look for: moisture level fluctuations in the soil, poor drainage or plumbing leaks, loss of soil compaction, tree roots or large plants near the foundation, improper or negligent construction, and soil erosion, flooding or natural disasters. Four of those six are water. That is why soil moisture management is the cheapest foundation work you will ever do.
If you cannot tell which foundation type you have, say 'not sure' on the form. Every company that visits will identify it in the first five minutes, and if the house turns out to be post-tension, that is information you want before anyone brings a core drill.