Replacing the building drain under a Calgary basement floor

01 /How do you know the problem is under the basement floor?

By comparing two measurements: the footage-counter distance to the defect, and the distance from the cleanout where the camera went in to the inside face of the foundation wall. If the defect reads shorter than the wall distance, it is under your slab. If it reads longer, it is outside, and the usual yard dig applies.

Because the counter follows every bend, a sonde check from inside the house is worth the extra minutes. The operator parks the camera at the defect and finds it with the receiver on the basement floor, so the saw-cut can be marked exactly. Finding the exit wall in the first place is covered in finding where your sewer line runs.

Older Calgary houses often have cast iron or clay under the slab, sometimes with later plastic repairs spliced in. Cast iron can scale and rot along the bottom of the pipe, which a camera shows as a rough, flaking floor and a flat spot of standing water; clay shows the same joint defects it does outside.

02 /Does replacing the building drain need a Calgary plumbing permit?

Plan on one. The City of Calgary's homeowner permit page says a plumbing permit is required when a plumbing system is constructed, extended or altered and when water and sewer lines in or around the home are replaced, while repairing a leak or removing a blockage in the drainage system is listed as not needing one. A new length of building drain under the floor is a replacement, so treat it as permit work and confirm the details for your job with the City.

• Contractor jobs: the plumbing contractor pulls the permit in its own name. Calgary plumbing permits covers who applies and how.
• Owner jobs: the homeowner permit is only for the legal owner who lives in the home, or intends to, and does the work personally.
• Combined jobs: if the yard lateral is also being replaced, ask for one scope that covers both, so the permit, inspections and the joint at the wall are handled together.
• Inspection before the floor is closed: the new pipe, joints, grade and bedding must be visible to the inspector. The concrete patch waits.

03 /What happens inside the house during an under-slab replacement?

An indoor sewer replacement is shallow compared with a yard trench, but every bucket of soil and concrete leaves the house by hand. Expect a crew to spend most of a day on demolition and protection before the old pipe is even visible.

1. Clear and protect

   Furniture and storage come out of the work area and the path to the door. Floors along the path are covered, and the work zone is sealed with plastic sheeting to contain dust.

2. Mark and saw-cut

   The trench line is marked over the pipe, often roughly half a metre wide, and the slab is cut along both edges with a wet or dust-controlled saw.

3. Break out and dig

   The concrete is broken between the cuts and removed; the soil below is dug by hand to the pipe, keeping clear of the footing.

4. Replace the pipe

   The old drain is cut out, soft or disturbed soil is replaced with bedding, and new pipe is laid to a continuous fall toward the exit wall.

5. Reconnect branches

   Floor drain, toilet, stack and any other branches are re-joined with proper fittings, and any backwater valve in the plan is set in place.

6. Camera and inspect

   The new run is filmed and the inspector checks it before anything is buried.

7. Backfill and patch

   Bedding and compacted fill go back in lifts; any sheet or membrane that was under the old slab is restored, and the concrete is patched and left to cure.

04 /Should a backwater valve go in while the floor is open?

It is the obvious time to decide. The City of Calgary's plumbing advisory on backwater valves, dated October 4, 2022, notes that the National Plumbing Code 2020 requires fixtures located below the level of the adjoining street and subject to backflow to be protected. In a Calgary basement, floor drains, basement toilets and showers usually fall in that group.

The City's new-house page adds that all new houses in the floodway, flood fringe or overland flow areas require a backflow valve. Whatever is installed must stay reachable: an access cover over the valve, not flooring laid over it. Day-to-day valve care is covered at CalgarySewers.com, and national backwater-valve pricing at SewerQuotes.com.

05 /How does a basement suite change the job?

It changes both the plumbing layout and the household plan. The same advisory states that secondary suites are considered a separate dwelling unit under the National Plumbing Code 2020 definition, so a normally open backwater valve cannot serve the suite and the main house together. The drain layout under the floor decides where protection can go, which is why suites deserve a separate conversation before the saw comes out.

• Map the branches first. Which fixtures belong to the suite and which to the main house, and where do they join the building drain?
• Decide protection per unit. Ask the plumber and the City how each dwelling unit will be protected under the current code.
• Plan for the occupants. A suite loses its bathroom and floor space for the length of the job; agree dates, access and alternatives with the occupants in writing, and follow the notice rules that apply to your tenancy.
• Keep the paperwork together. The permit, inspection and valve details are part of the suite's record, alongside any suite approvals.

06 /How does indoor work fit with a yard replacement?

When the footage shows defects on both sides of the wall, one continuous scope is cleaner than two separate jobs. The joint at the foundation is the critical point: the indoor pipe and the outdoor lateral should meet at matching grade with a proper coupling, inspected before either side is covered.

The yard side runs as described in what a sewer replacement crew does day by day, and trench protection for the deep part is covered in trench safety on a Calgary sewer dig.

07 /What should you plan for finished basements?

Finishes are usually the slowest part of an indoor sewer job to put back, and they are rarely in a plumbing quote unless you ask. Walk the trench line with the contractor and list everything it crosses.

1. Flooring over the trench line: carpet, laminate, vinyl plank or tile, and whether spare material exists to match.
2. Walls or built-ins the trench passes under, and whether a wall must be opened to reach the stack.
3. Heating ducts, in-floor heat or electrical runs in or under the slab near the pipe.
4. Who restores each finish, and when: the plumber, a flooring trade, or you.
5. Where the old concrete and soil will be staged outside and how the path through the house is protected.

When the indoor section is scoped, add it to the Permit & Locate Checklist and request quotes that list the indoor and outdoor lengths separately.

FAQQuestions people ask