Under-slab sewer repair in Houston: tunnels and reroutes

Why this is a Houston problem

Between about 1950 and 1975, the ranch houses in Meyerland, Bellaire, Oak Forest, Westbury, Sharpstown, Spring Branch and Braeswood were built on post-tension or conventional slabs with cast iron drain lines cast into them. The pipe has spent sixty years in gumbo clay that swells in a wet May and shrinks in a dry August. The slab moves; the cast iron does not. Hubs crack, the pipe floor rusts through, and the drains start leaking into the clay under the middle of the house.

The leak feeds the clay, the clay heaves, and the house gets a foundation repair. The leveling moves the slab again and finishes off the joints that were barely holding. That is why so many under slab sewer repair Houston jobs start with a foundation company: they ran the post-repair hydrostatic test, it failed, and now the homeowner has a second problem.

Sewer leak detection in Houston slab homes

Finding the leak comes before fixing it. Sewer leak detection in Houston starts with a hydrostatic test to confirm the drains are losing water, then isolation testing — plugging branch lines one at a time — to find which run is leaking, then a camera with a sonde down that run to put the failure on the floor plan, with its distance from the nearest exterior wall. Without that, any under-slab quote is a guess.

The three fixes

Tunneling. A crew hand-digs a tunnel about 3 feet wide and 3 feet high from the outside edge of the slab to the failed pipe, shoring as they go, replaces the cast iron with PVC, and backfills. Tunnels in Houston are priced by the foot — typically $150–$250 per foot — plus the plumbing. A leak 15 feet in from the wall under a hall bath is a $4,000–$9,000 job. A leak under a kitchen island in the middle of a 60-foot-wide house is $15,000–$25,000, because the tunnel is the cost.

Reroute around the slab. Instead of reaching the old pipe, abandon it. New drain lines are trenched outside the foundation from the fixtures nearest an exterior wall to a new run that ties into the main, keeping the downhill fall a gravity drain needs (this is different from an overhead repipe of water supply lines, which can go through the attic because they are under pressure). There is no tunnel under the living space. It suits houses where the failed section serves fixtures along an outside wall; fixtures in the middle of the slab still need a tunnel or spot repair. Typically $8,000–$20,000 for a full reroute of a bathroom group. Houston sewer reroutes compares the two on a real layout.

Lining from the inside. When the cast iron is still round and the failure is corrosion rather than a separated hub, a cured-in-place liner can be installed through the cleanouts, then the branch connections reopened with a robotic cutter. No tunnel. It fails when the pipe has collapsed, when the branches are too many to reinstate economically, or when the pipe has a belly. The trenchless page covers it.

Some jobs mix them: tunnel to one section under the master bath, line the run to the kitchen, leave the rest of the house alone because the camera showed it is fine.

Cutting the slab

The fourth option is breaking through the floor from inside. It is fast and cheap for a single fixture, and it is what many plumbers who do not tunnel will offer. Its problem is the floor: terrazzo in a Meyerland ranch, wood over slab, or tile that cannot be matched. It also means living in the dust. It makes most sense when the leak is right under an easily replaced floor and nowhere else.

How the decision usually gets made

1. A hydrostatic test to confirm a leak, then isolation testing to find which run under the slab is losing water.
2. A camera through that run with a sonde, so the spot is known to the foot along with its distance from the nearest exterior wall.
3. A written price for the tunnel and for the reroute where both are possible, so you can see the trade-off on paper. Ask for both.
4. A plumbing permit pulled by the licensed plumber and a city inspection before the tunnel is backfilled. Engineers' letters for post-tension slabs where the tunnel passes near a cable.
5. A second hydrostatic test on the finished work. Ask for both results in writing.

After foundation repair

If a foundation company has just leveled the house, get the drain test before they leave, or within days. The test is $250–$500. A failed test days after leveling is a plumbing fix; a slab that heaves again a year later because a leak was never found is a second foundation bill. Some Houston foundation warranties are written to require a passed plumbing test, so read yours.

Signs the trouble is under the slab

Some symptoms point under the house rather than out to the yard. None of them proves it, but two or three together are worth a hydrostatic test:

• A sewer smell in one bathroom that comes and goes, with no clog to explain it
• A slow drain in a back bathroom or a laundry room, while the drains near the front of the house run fine
• New cracks in tile, sheetrock corners or brick, or doors that start to stick after years of closing fine
• A damp or warm patch in a floor, or a carpet edge that smells musty
• Gnats or small drain flies near a floor drain or a tub that is not used much
• A foundation contractor who has found a leak, or a test that failed after leveling

The camera in the yard will not see any of this, because the problem is upstream of it. Ask for the test, and then for isolation, before anyone prices a tunnel.

What it costs

Typical market ranges, not a quote. The wide spread you see between Houston contractors on this work is usually a tunnel versus a reroute quoted against each other without saying so; the pricing page explains how to line them up. Bellaire is where this work is most concentrated, and the Bellaire page has more on the housing there. Whoever you hire for under-slab work must be a licensed Texas plumbing company — check the license on the TSBPE website.