Post-Tension Slabs
in Houston, TX

How much does a post-tension slab cost in Houston, and is it more than rebar?

We quote every post-tension slab per job, after we have read the stamped plan. A per-foot rate given before the soil report is a guess, so we do not publish one. Here is what moves the number: slab size, beam depth and beam count (both set by the PVR), tendon count, psi and select fill. Access matters too, along with the vapor retarder and whether old concrete has to come out. Post tension slab cost versus rebar depends on the ground. On clay with a high plasticity index, a stressed slab often costs about the same as a rebar slab built stiff enough for the same movement. It also uses less concrete in the beams. On stable soil, rebar can be the cheaper call. Ask for the free written estimate and you get every line.

Is a post-tension slab better than a rebar slab on Houston clay, and what are the downsides?

Rebar holds a crack tight after it forms. Tendons squeeze the slab together so cracks are less likely to open in the first place. On clay with a plasticity index in the 40s and 50s and an active zone 10 to 25 feet deep, Houston engineers usually pick post-tension. Now the honest limits. You cannot cut or core a stressed slab without scanning it first. Moving a drain line under it costs more. And a bad stressing job is invisible from the surface, which is why the elongation record matters more than any sales pitch. Where the soil report does not call for tendons, a conventional concrete slab with Grade 60 rebar does the job for less. The stamped plan makes that call.

What code does a post-tension slab have to meet in Houston, and do I need a permit?

Houston builds to the 2021 IRC and IBC, effective January 1, 2024. The code calls soil expansive at a plasticity index of 15, and Houston clay is often three times that. The 2021 code Houston uses sends post-tensioned slabs on expansive soil to PTI DC10.5, the Post-Tensioning Institute standard. In Texas a licensed engineer stamps that design, and we build to the stamp. The permit comes from the City of Houston inside city limits. On commercial work the city will issue a Foundation Only Permit so the pad can start during plan review. Outside the city line, the permit comes from the Harris County Engineering Department on Fannin Street. Houston also requires a form survey at the first structural inspection, and the finished floor sits at least 12 inches above the nearest sewer manhole rim. We pull the permit and book the inspections.

Why do post-tension slabs crack or fail, and can they be repaired?

Hairline shrinkage cracks are normal and do not mean the tendons failed. Real post tension slab failure almost always starts at the ends. Think of an anchor that was never capped, a sheath cut before the pour, a pocket grouted with the wrong mix, or water reaching bare strand. Trees are the number one cause of foundation repair work in the Houston area, per the Foundation Performance Association, and a slow plumbing leak wets one spot and lifts it. Houston swung from 24.57 inches of rain in 2011 to 79.69 inches in 2017. Clay that sees both is why tendons earn their keep. Watch for doors that stick, a floor out of level, or a tendon end that has popped at the slab edge. Yes, it can be repaired. Piers, leveling and tendon splicing are all real fixes. Start on our foundation repair page or call (832) 576-3278.

How do I know if my slab is post-tensioned, and what happens if I drill or cut into it?

Look at the garage floor near the door. A stamp that says post-tension slab, do not cut or core, is your answer. No stamp? Look for round grout patches 1.5 to 3 inches across every 2 to 4 feet along the slab edge. Those are tendon ends. A stressed tendon holds tons of force. Cut one and it can whip out of the slab and hurt someone, and the slab loses the squeeze it was designed for at that spot. So scan before you cut, every time. We locate tendons with ground-penetrating radar before any core, saw cut or plumbing move, then cut between them. Need a floor drain, a lift pocket or a trench in an existing post-tension slab? See our concrete cutting and core drilling page before anyone picks up a saw.

How long does a post-tension slab last, and when do the tendons get stressed?

Built to plan and kept at even moisture, a post tension concrete slab lasts the life of the building. The strand is 270 ksi low-relaxation steel, greased and sheathed so water never touches it. Stressing happens once the concrete reaches the strength on the plan. Residential tendons are usually stressed 3 to 10 days after the pour, and owner specs like the University of Houston's say not to stress below 3,000 psi. We mark each strand, pull it, measure how far it moved, and check that number against the engineer's calculation. Tails get cut and pockets get non-shrink grout only after the engineer approves the record. After that, the slab's life is mostly up to the yard. Keep grade sloping 2 to 5 percent away from the slab, fix leaks fast, and keep big trees back from the edge.