Under the slab
Under-slab sewer repair in San Diego
Clairemont, Allied Gardens, Serra Mesa, the flat parts of La Mesa and Chula Vista: post-war ranch houses on a concrete slab, with cast iron drain lines cast into the ground underneath. Sixty years on, the bottoms of those pipes are rusting through, and the fix is a different job from a yard lateral.
How you find out
A slow kitchen sink that a cable fixes for a month. A wet spot on the slab in the hall. A smell in one bathroom that comes and goes. Cockroaches or drain flies from a floor drain. Or nothing at all until a camera inspection before a remodel finds that the last 30 feet of pipe under the house has no bottom. (A "slab leak" with warm flooring is usually the water line, not the drain.)
Cast iron corrodes from the inside, on the floor of the pipe where the water sits. The top of the pipe looks fine on a camera for years after the bottom has opened up. Once it does, wastewater soaks into the soil under the slab, and in expansive clay that means the ground swells. Heaved tile, a door that sticks in winter, and a foundation contractor in the conversation.
Three ways to fix it
Lining in place. If the pipe is still round enough to hold a liner, it's cleaned, descaled and lined with CIPP from a cleanout or a pulled fixture, with the branch connections reinstated by a robotic cutter. No concrete cut at all in most cases. This is the first option to look at for an under-slab line, because it's the least disruptive and the same trenchless methods used in the yard work just as well under a house.
Tunneling. A crew hand-digs a tunnel from outside the foundation, under the footing, along the pipe. The old pipe is replaced with ABS in the tunnel and the soil is packed back. Nothing inside the house is touched. Slower and priced per foot of tunnel, but it keeps the floors intact, which matters when the floors are original oak or the kitchen was just done.
Cutting the slab. Saw-cut the concrete over the pipe, dig, replace the pipe, backfill, pour. Cheapest per foot and the right call when the floor is coming up anyway for a remodel, or when the failed section is short and in a garage or utility room.
Re-routing overhead is the fourth option on some houses: abandoning the under-slab line and running new drains through the attic or along an exterior wall to a new connection. It works for a bathroom on an outside wall and not much else, and a good contractor will say when it's the cheaper path.
Cast iron pipe replacement: San Diego slab homes usually mix these methods, lining the long runs and cutting the slab only where a short section has collapsed.
What it costs
| Method | Typical San Diego range |
|---|---|
| CIPP lining under the slab, per foot | $150 – $300 |
| Tunneling, per foot | $250 – $450 |
| Slab cut and replace, short section | $3,000 – $8,000 |
| Full under-slab re-pipe, 3-bed ranch | $12,000 – $30,000 |
A single failed run under a kitchen is often $4,000–$9,000. A whole-house under-slab job on a 1955 Clairemont ranch, all the cast iron gone, is the top of that table, and it's the job where the difference between lining and cutting the floor is the whole cost of a new kitchen floor. The cost page sets these next to the yard-lateral prices.
Under-slab and the lateral together
The lateral from the house to the street is usually the same age as the pipe under the slab. Camera both on the same visit. Replacing one and leaving the other is the most common way to pay for the same problem twice, so insist on the whole picture, then phase the work if you need to. Sewer line replacement covers the outside half.
The foundation question
If the slab has already heaved or cracked, it may need a foundation contractor as well. A careful contractor won't line a pipe under a slab that's actively moving without a conversation about why; the ground under it is wet for a reason, and the leak is often the reason. Drought, soil shrink and pipe breaks explains how San Diego's clay does this to a slab.
What the job involves, step by step
- Camera and locate. The under-slab lines are cameraed from a cleanout or a pulled fixture, and each problem is marked on the floor with its depth.
- Testing, if needed. Where the camera can't tell, the system is plugged and filled to see whether it holds water.
- Choosing the method. Lining, tunneling, a slab cut, a re-route, or a mix. The footage and the floor finish decide.
- Cleaning. Cast iron is descaled by hydro jetting until the wall is visible. Lining over heavy scale doesn't hold.
- The work itself. A liner cured in place, a tunnel dug from outside, or a saw-cut opening over a short section.
- Branch lines. Each tie-in from a sink, tub or toilet is reopened or reconnected.
- Inspection and an after video. Ask for both, and keep them with the house records.
Questions to ask before you choose a method
- Which runs are still round enough to line, and which are not?
- If the slab must be cut, where exactly, and what flooring sits on top?
- Is tunneling possible from outside the foundation on this side of the house?
- How many branch lines are there, and is each one in the price?
- Will the lateral outside be cameraed and priced on the same visit?
Living in the house during the work
Most lining jobs take one to two days. You'll lose drains for part of that time, so plan meals and showers around the window. A slab cut means dust, noise and furniture moved out of one room. Tunneling is quieter inside but takes longer. Ask for a day-by-day plan in writing, including when water can be used again.
Common mistakes on under-slab jobs
- Cutting the floor before anyone has asked whether the line can be lined
- Lining a pipe that wasn't fully descaled, so the liner can't bond
- Fixing one run and never cameraing the other branches under the house
- Repairing the pipe while the slab is still moving, with no word to a foundation contractor
- Paying for new flooring before the after video confirms the pipe is sound
Other sewer services
Sewer Line Repair
Backups cleared, roots cut, the line hydro jetted and cameraed, and a spot repair where one section is broken and the rest is sound.
Sewer Line Repair →Sewer Line Replacement
A new lateral from the house to the main when the old cast iron or clay is done. Open-trench where it makes sense, trenchless where it doesn't.
Sewer Line Replacement →Trenchless Sewer Repair
Pipe lining and pipe bursting through one or two small pits, so the driveway, the patio and the city sidewalk stay where they are.
Trenchless Sewer Repair →Sewer Camera Inspection
A recorded camera run from the cleanout to the main, with the break located from the surface. The basis for every honest quote, and the first thing to do before buying an old house.
Sewer Camera Inspection →Drain Cleaning
Fixture clogs and main-line clogs told apart, snaking vs hydro jetting explained, and the camera check that shows whether the clog was the whole problem.
Drain Cleaning →Questions plumbers get asked
How do you know a drain leak is under the slab?
A camera inspection with a sonde locate. The camera is run to the bad section and the sonde traced from above to mark the spot on the floor and read the depth. Where the camera can't get through, a hydrostatic test of the under-slab system, plugging the line and watching the water level, confirms whether it's holding.
Will the floors have to be broken up?
Often not. Lining runs from a fixture or cleanout and needs no concrete cut. Tunneling reaches the pipe from outside the foundation. Cutting the slab makes sense when the failed section is short and the floor is cheap or coming up anyway. The camera footage decides; ask to see where each option lands on the quote.
Does homeowners insurance cover an under-slab sewer leak?
Sometimes partly. Many policies exclude the pipe itself but may cover access, the floor and water damage inside; read your policy and ask your agent. A service line endorsement is usually a modest add-on — ask your agent for the price, the limit and the deductible. See does homeowners insurance cover sewer line repair.
Can under-slab cast iron be lined if it has a hole in the bottom?
Often, if the rest of the pipe is still round and the hole is short. The liner bridges small gaps once the line is descaled. A long stretch with no floor at all, or a section that has crushed, usually needs a slab cut or tunnel at that spot first. The camera footage settles it.
Need sewer line work in San Diego?
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