Interior drainage and sump pit

Sometimes the outside of the wall cannot be reached. A driveway runs to the foundation, the neighbour's house is a metre away, a mature maple sits where the trench would go, or the landscaping is worth more than the repair. Interior drainage is the answer in those cases, and it is also the option that can be done in February when a family is dealing with a flooded basement and cannot wait for May.

Be clear about what it does. An interior system does not keep water away from your foundation. Water still reaches the wall and still enters at the footing joint. What the system does is catch it there, below the floor, and move it to a pump before it can reach the room. For a homeowner who wants a dry, usable basement, that is often the outcome that matters. For a homeowner worried about the wall itself, it is a different conversation.

Step one: planning the route and the pit. The crew maps the perimeter, decides where the sump pit goes, usually at the lowest corner near an electrical supply, and identifies what has to be moved. Finished basements need the bottom of the drywall and the baseboards off along the affected walls.

Step two: cutting the slab. A strip of concrete roughly 300 to 400 mm wide is saw-cut and broken out along the wall. This is dusty, loud work, and a contractor should be using dust extraction and poly containment rather than opening windows and hoping. The debris goes out by bucket or conveyor.

Step three: laying the drain. A trench is dug beside the footing, perforated pipe is bedded in clear stone, and it is sloped to the pit. Weep holes are often drilled into the base of block cavities so water trapped inside the block can escape into the new drain rather than sitting there. A vapour barrier is set against the wall to direct water down into the stone.

Step four: pit, pump and re-pour. A pit liner is set, the drain lines enter it, and a pump sized to the house is installed with a check valve and a discharge line that leaves the house and daylights well away from the foundation. The trench is re-poured in concrete, finished flush with the existing slab.

Step five: the backup. In Ottawa this is not an optional extra. The storms that produce the most groundwater are the same storms that take the power out, and a sump pump on a dead circuit is an ornament. A battery backup pump, or a water-powered backup where the plumbing suits, is the difference between a system and a hope.

How long it takes. Most interior perimeter jobs run three to six working days: a day of preparation, two or three of cutting and installing, a day of pouring, then cure time. The concrete needs roughly a week before heavy loads go back on it and around 28 days to reach full strength, so hold off on reinstating a finished floor.

What it costs in Ottawa in 2026. Indicative ranges only. A full interior perimeter system with a sump is commonly $10,000 to $22,000. A partial run along one wall is proportionally less but rarely proportionally cheap, because mobilization, the pit and the pump are fixed costs. A sump pump replacement on its own, in an existing pit, is generally a few hundred dollars plus the pump. What moves the total: the perimeter length, whether a pit already exists, how much finished basement has to come apart and go back, and what the discharge run outside involves.

What makes an Ottawa house different, and a City programme worth knowing. Champlain Sea clay drains badly, which is why sump pits are close to standard in the newer suburbs and why an interior system here is usually pumping rather than gravity-draining. More usefully, the City of Ottawa's Residential Protective Plumbing Program pays a subsidy toward protective plumbing work, including $3,000 toward a sump pump installed in a new pit and $1,500 toward one in an existing pit, plus 100 per cent of the building permit fee (City of Ottawa). Eligibility depends on when the house was built, the work has to be done by a licensed plumbing contractor under a permit, and the application has a deadline, so read the current rules at ottawa.ca/rppp before you sign anything.

Who should do the work. Plumber is a compulsory trade in Ontario, which means the plumbing side of this, the pump, the check valve and the discharge connection, must be done by someone holding a valid Certificate of Qualification, and you can check a name yourself on the Skilled Trades Ontario public register. That is also what the City's subsidy requires. The concrete and drainage work itself is not licensed, so judge it on insurance, WSIB coverage and a written warranty.

What to ask before you hire. What pump, what horsepower, and what is its warranty. Is a battery backup included and how long will it run. Where does the discharge go and how far from the foundation. Will you drill weep holes in block walls. Is the electrical work included, and by a licensed electrician. Does the price cover removing and reinstating finished walls. Will you handle the City rebate paperwork, and is the plumbing being done by someone with a current Certificate of Qualification.