2026-03-05 — Ottawa-Gatineau
Adding a basement bathroom, replacing a sewer pipe, installing an interior French drain or a backwater valve: in all these cases, the concrete floor must be opened. Here's exactly how it goes, with photos from one of our real job sites.
Projects that require opening the slab
- New basement bathroom or laundry room — the classic: a trench is opened to run drain and water pipes
- Sewer pipe replacement — common in older Ottawa and Hull homes (cast iron or clay pipes)
- Interior French drain — perimeter trench against water infiltration
- Backwater valve — sometimes required or subsidized by the City of Ottawa or Gatineau
- City service connections — water or sewer
How the job site goes, step by step
1. Layout
We locate existing pipes and mark the cut lines. Precision matters: the less we open, the cheaper it is to close back up.
2. Diamond cutting
The flat saw cuts two straight parallel lines in the slab — usually 4" thick, sometimes more with rebar. Wet cutting: no dust in the house.
3. Breaking and excavation
We break the concrete strip between the cuts, remove the gravel underneath, and the trench is ready for the plumber.
4. Plumbing
The plumber installs the pipes — drains, sewer, water supply. On our job site below, it was a connection to city services.
5. Closing back up
Compacted gravel, then a new concrete pour to level. After a few days of curing, the floor is as good as new — ready for tile, vinyl or epoxy.
How much does it cost?
For cutting and opening a typical basement trench (plumbing and closing are billed separately). A full perimeter trench for a French drain: often $1,500 to $3,000 of cutting depending on house size.
Mistakes to avoid
- Digging without cutting first — jackhammering without pre-cutting leaves jagged edges and cracks the surrounding slab
- Forgetting to locate pipes — cutting a water line or electrical wire under the slab is expensive
- Closing before inspection — if a permit is required, the inspector must see the pipes before the pour
Have a basement plumbing project? See our slab sawing service →