The short answer
A slab leak and a foundation problem can each cause the other. Leaking water swells the clay under part of a slab; a foundation that moves, or is lifted during repair, can crack the pipes cast beneath it. The Texas ASCE guidelines say that whenever a repair includes jacking or lifting, water supply and drain lines should be tested for leaks, and leaks found should be repaired.
How a leak moves a foundation
Clay swells when it gets wet: a Texas licensing bulletin describes it as heave when wet, settle when dry. A leaking drain line under the middle of a house can keep one patch of clay soaked for months. The result is often center heave: a hump in the floor, interior cracks, and doors binding in the middle of the house while the outside walls look fine.
Leaks also undermine repairs. The Foundation Performance Association warns that moisture near a pile from poor drainage or leaking sewer or water lines can cause the pier to move. A house piered without fixing a leak can start moving again.
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Signs that point to a leak
- A water bill that jumps with no change in use.
- The sound of running water when every fixture is off.
- Warm spots on the floor, which can mean a hot water line leaking.
- Damp carpet, lifting floor tiles, or mildew with no visible source.
- A hump or crack pattern in the middle of the house rather than at the edges.
- Slow drains or a sewer smell inside.
None of these proves a leak on its own. A test does.
The tests and what they show
| Test | What it checks | Who does it |
|---|---|---|
| Hydrostatic (drain line) test | The sewer line is plugged and the drains filled with water; a falling level means a leak in the drain system | A plumber; TREC’s addendum for buyers calls for a licensed plumber |
| Water supply pressure test | Fixtures are shut and the supply lines held under pressure; a drop means a supply leak | A plumber |
| Leak location | Acoustic or electronic equipment pinpoints where under the slab the leak is | A plumber or leak-detection company |
| Engineer’s Level C evaluation | Testing an engineer adds when the cause is unclear, which can include soil, plumbing and material testing | A licensed engineer you hire |
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Test before the lift, and after
The order matters. A test before repair answers two questions: is a leak part of what’s moving the house, and were the pipes intact before the lift? A test after the lift catches anything the lift itself cracked. Without the first test, nobody can say which came first, and the warranty and insurance conversations get harder.
Ask the contractor:
- Is a plumbing test included, before, after or both?
- Who runs it, and do I get the written results?
- If a leak turns up mid-job, who repairs it, and how is it priced?
Who can repair the pipes, and the permit
Texas law reserves plumbing work, including repairs to water lines under a slab, for licensed plumbers under the state’s Plumbing License Law. Fort Worth adds a permit: changing, moving or repairing plumbing requires a plumbing permit, separate from the foundation repair’s building permit. Plumbing found broken during a foundation job is therefore its own piece of work, done and permitted by a plumber.
Reaching a pipe under a slab means either breaking through the floor inside or tunneling from outside. Fixr puts the average slab leak repair, including detection, tunneling and patching, at $2,500.
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Insurance: what to do first
Settling from dry or shifting soil is almost never covered, but a sudden plumbing leak can be:
- Under the older Texas HO-B policy, a covered water leak includes the cost of tearing out and replacing the parts of the house needed to reach the pipe. The Texas Supreme Court held in 1998 that the HO-B’s foundation exclusion doesn’t bar a claim for foundation damage caused by a plumbing leak.
- Insurers have written their own forms since 2003, so your policy may differ. Some add a foundation endorsement for plumbing-leak damage.
- The Texas Department of Insurance notes that policies cover sudden discharges but not leakage that went on past a set period: report a leak as soon as you find it.
- Don’t make permanent repairs before the insurer has seen the damage; TDI warns that the company might deny the claim if you do.
The insurance guide lays out what’s usually covered and what isn’t.
Where this fits in a repair plan
For a slab house with signs of heave, a plumbing test is often the first step, ahead of any pier plan. For a house with edge settlement, it’s still worth testing before a lift, especially in older Fort Worth houses where the pipes under the slab are as old as the house. The slab repair page walks through the repair itself.