Installation

Sewer Reroutes vs Tunnels: Getting Under the Slab

By Houston Sewer Repair · October 25, 2026 · 8 min read

The widest spread in quotes a Houston homeowner will ever see is for the drains under a slab. One contractor says $6,000. Another says $28,000. Both looked at the same house. The difference is usually not honesty; it is that one priced a single failed section and the other priced abandoning every drain in the house, and neither said so. Houston sewer reroutes and under-slab tunnels are the two main ways in, and the choice between them comes down to a few measurements. Here is how the decision gets made, on a typical Houston floor plan.

The house

This is a composite example, not a specific job. A 1963 one-story ranch in Meyerland, about 2,100 square feet, three bedrooms, two baths, kitchen in the middle of the house. Slab foundation, cast iron drains, no cleanout. The foundation was leveled with pressed piers in the spring after doors started sticking. The foundation company ran a hydrostatic test afterward and it failed. The homeowner has a sewer smell in the hall bath and a warranty that says the plumbing has to pass.

Step one: find which run is leaking

A hydrostatic test says "something under the slab leaks." It does not say where. The drains under this house form a tree: the hall bath group on one branch, the master bath on another, the kitchen and laundry on a third, all meeting at the building drain that leaves the slab on the east side.

Isolation testing plugs each branch in turn, through a pulled toilet or a tub drain, and fills only that section. On this house the hall bath holds; the master bath holds; the kitchen and laundry run drops an inch in ten minutes. That is the leak. It took an hour and it changed the job from "the drains under the house" to "the kitchen line."

Step two: camera the run

Through the pulled kitchen sink trap, the camera goes into the 2-inch kitchen branch and follows it to where it joins the 3-inch main run under the slab. At 19 feet from the sink it finds a separated hub — the camera shows a gap and clay behind it. The locator on the floor above marks the spot: under the hallway between the kitchen and the utility room, 31 feet from the east grade beam and 14 feet from the north one.

That second measurement is the whole cost question. The leak is 14 feet from the nearest exterior wall.

Step three: price the ways in — sewer reroute vs tunnel

Tunnel from the north wall. A hand-dug tunnel, about 3 feet wide and 3 feet high, from the north grade beam 14 feet in to the hub, shored as it goes, roof of the tunnel being the slab itself. Replace the failed hub and the sections either side in PVC, tie into the sound cast iron with proper transition couplings, inspect, backfill with sand in compacted lifts. On post-tension slabs the cables get located first and the tunnel routed between them; this 1963 slab is conventional.

Tunnel, 14 ft at $150–$250/ft: $2,100–$3,500
Plumbing, permit, inspection, second hydrostatic test: $2,000–$3,500
Total $4,500–$7,500, three days.

So the under-slab tunneling cost on this house is set mostly by those 14 feet.

Reroute of the kitchen and laundry. Abandon the cast iron under the slab for that branch. Run new PVC drains from the kitchen sink and the washer out through the north exterior wall to a new line trenched outside the slab, keeping the downhill fall a gravity drain needs, and tie it into the lateral. No tunnel, but the wall gets opened in two places and the drywall repaired.

Plumbing, permit, inspection: $6,000–$10,000
Drywall and paint: $800–$1,500
Total $7,000–$11,500, four to five days.

Whole-house replacement. Tunnel to every run and replace all the cast iron under the slab. About 90 feet of tunnel on this plan.

$22,000–$30,000, two weeks.

Cut the slab from inside. Break the floor in the hallway, dig down to the hub, repair, patch the slab.

$2,500–$5,000, two days, if the floor is sheet vinyl over concrete. On terrazzo or wood, the floor repair costs more than the tunnel.

Step four: how Houston sewer reroutes compare on this house

On this house the camera passed clean through the hall bath and master runs. The cast iron is rough but round and holding water. So the whole-house number is the wrong job for this year. The reroute would make sense if the kitchen run were failing along its whole length, or if the kitchen were being remodeled anyway. It is not. The slab cut would save money if the hallway floor were cheap; it is original terrazzo.

The tunnel wins: $4,500–$7,500, and the hall bath and master runs go on a watch list, with a camera every few years so the next failure is planned rather than met as an emergency. That is the difference between the $6,000 quote and the $28,000 one, and it is why under slab sewer repair Houston contractors quote should always say which section, which method, and what the rest of the pipe looked like.

What happens on a tunnel job

Texas811 locate along the north wall, and the sprinkler zone there shut off.
The tunnel crew digs by hand, hauling spoil out in buckets, shoring every few feet. Two people, about two days for 14 feet.
A licensed plumber replaces the hub and adjacent sections in PVC, with the camera confirming the connection both ways.
Inspection with the tunnel open, where the city requires it — the permit office will confirm.
Backfill: sand in lifts, compacted, so nothing settles under the slab. Some jobs use flowable fill.
A second hydrostatic test on the whole system. The recording and the test results go to the homeowner, and to the foundation company if its warranty asks for them.

Common questions

Is tunneling under a slab better than breaking the floor?

Often, but not always. A tunnel leaves the inside of the house alone, which matters on terrazzo, tile or wood floors and in a lived-in home. Cutting the slab from inside can be cheaper when the failure is under cheap flooring close to where you can work, so ask for both prices when both are realistic.

How long does an under-slab tunnel take?

A short tunnel of 10–20 feet is usually a two-to-three-day job including the repair, inspection, backfill and retest. Longer tunnels to several runs can take one to two weeks. The contractor should give you the schedule, including the hours or days the drains will be out of use.

Will a reroute leave pipes visible in the house?

Usually not much. A drain reroute leaves the house through a wall near the fixtures and runs in a trench outside the slab, so inside you see patched drywall where the wall was opened. Outside, the new line is buried along the foundation. Ask to see the planned route on the floor plan before you sign.

Can the rest of the cast iron just be lined instead?

Sometimes. Lining needs a pipe that is still round enough to hold a shape, and the camera decides that. Rough but round cast iron can often be lined from inside. Pipe with the bottom rotted through, or a hub that has separated, usually needs that section replaced first.

Mistakes that make an under-slab job cost more

Pricing before isolating. Without a branch-by-branch test, the only safe quote is the whole house. One hour of testing narrows it to one run.
Measuring from the wrong wall. The tunnel starts at the grade beam closest to the failure. Ask for both distances on the plan and the reason for the side chosen.
Forgetting the floor. A slab cut looks cheap until the floor is terrazzo, tile or wood. Price the floor repair before you choose it.
Skipping the second test. The retest proves the repair and the runs left alone. Some foundation warranties ask for it.
Letting the foundation crew and the plumber work blind. Leveling moves the slab. Book the drain test with the foundation job, not months after it.

How to compare two under-slab estimates

Put the quotes side by side and check that they describe the same job. Each one should name the run, the distance from the wall, the method, the footage of tunnel and the pipe being replaced. If one says "replace drains under house" and the other names the kitchen line at 14 feet, they are not the same job and the prices cannot be compared. Ask the higher bidder what they saw that the lower one missed. Sometimes the answer is real, such as a second failing hub. Sometimes it is a guess.

What to ask any under-slab quote

Which run leaks, and how was it isolated?
Where is the failure, and how far from an exterior wall?
What did the camera show on the runs you are not replacing?
Tunnel or reroute, and why that one?
Is the second hydrostatic test included?
What is the permit number?

The under-slab sewer repair page has the ranges for short and long tunnels and reroutes, and the pricing page puts them next to the yard-lateral numbers. On a Bellaire or Meyerland ranch, this is the job; the Bellaire page has more on the housing there.

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