Under the slab
Under-slab sewer repair in Houston: tunnels and reroutes
The drains under a 1960s Houston slab are cast iron sitting in wet clay, and they are failing on a schedule. There are three ways to fix them. The right one depends on where the leak is, how far it is from an outside wall, and what the rest of the pipe looks like — not on which one a contractor happens to sell.
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 phone call from a foundation company: they ran the post-repair hydrostatic test, it failed, and now the homeowner has a second problem.
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.
Overhead reroute. Instead of reaching the old pipe, abandon it. New drains run from the fixtures up through the walls and attic, and down an exterior wall to a new line outside the slab. There is no tunnel and no slab cut. The cost is in opening walls and ceilings, so it favors houses that are being remodeled anyway, or where the failed pipe is far from any outside wall. Typically $8,000–$20,000 for a full reroute of a bathroom group.
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 most 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. We do it when the leak is right under an easily replaced floor and nowhere else.
How we decide
- Hydrostatic test to confirm a leak, then isolation testing to find which run under the slab is losing water.
- Camera through that run with a sonde, so we know the spot to the foot and its distance from the nearest exterior wall.
- A written price for the tunnel and for the reroute where both are possible, so you can see the trade-off on paper.
- A plumbing permit and a city inspection before the tunnel is backfilled. Engineers' letters for post-tension slabs where the tunnel passes near a cable.
- Second hydrostatic test on the finished work. You get both results.
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. Several Houston foundation warranties are written to require a passed plumbing test, and the Texas Department of Insurance guidance on foundation claims points the same way.
What it costs
| Job | Typical Houston price |
|---|---|
| Hydrostatic test and isolation | $250 – $700 |
| Tunnel, per linear foot, with shoring and backfill | $150 – $250 |
| Short tunnel, one section, hall or master bath | $4,000 – $9,000 |
| Long tunnel or two bathrooms | $12,000 – $25,000 |
| Overhead reroute, one bathroom group | $8,000 – $20,000 |
| Slab cut and patch, single fixture | $2,500 – $6,000 |
Typical 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, and under-slab sewer repair on Houston homes goes through a real layout. Bellaire is the neighborhood where we do this most, and the Bellaire page has more on the housing there.
Other sewer services
Sewer Line Repair
One broken, separated or bellied section replaced in PVC after the camera finds it — dig or tunnel to that point only, $1,500–$4,000 typical.
Sewer Line Repair →Sewer Line Replacement
New schedule 40 PVC from the house to the property line, open trench, permitted and inspected — when the whole lateral has failed.
Sewer Line Replacement →Trenchless Sewer Repair
Cured-in-place lining or pipe bursting through one or two access pits — the fix when the line runs under a driveway, a pool deck or a live oak.
Trenchless Sewer Repair →Sewer Camera Inspection
A recorded look inside the line with the break located and marked on the surface — the $250–$500 visit that decides whether you need a $500 job or a $12,000 one.
Sewer Camera Inspection →Questions we get asked
Is tunneling under a slab safe for the foundation?
Yes, done with shoring and backfilled properly. Tunnels are cut from the exterior grade beam inward, the roof of the tunnel is the slab itself, and the tunnel is filled with compacted sand or flowable fill when the plumbing is done. On post-tension slabs we locate the cables first and keep clear of them. Foundation companies tunnel the same way to install their piers.
How long does under-slab sewer repair take?
A short tunnel is two to three days: dig, plumb, inspect, backfill. A 40-foot tunnel or a full overhead reroute is a week to ten days. You keep the use of the house throughout; the drains being worked on are out of service for a day or two at most.
Can I just keep snaking the line instead?
For a while. Cast iron with channel rot catches paper on the rough floor and clogs every few months, and each cable pass takes a little more metal with it. Snaking buys time, but the leak into the clay continues, and a slab that heaves from it costs more than the tunnel would have. The camera will tell you how much time you have.
Need sewer line work in Houston?
Call for a free estimate. Mon–Sat 7am–7pm.