Interior waterproofing in Toronto manages water after it reaches your foundation rather than stopping it outside. The slab is broken open along the footing, a drain is laid, and everything is routed to a sump pump.
Interior waterproofing in Toronto runs $80 to $150 per linear foot of foundation wall, or $8,000 to $15,000 for a full system. The work involves breaking the perimeter slab, laying perforated drain pipe in clear stone beside the footing, fitting a dimple membrane up the wall, connecting to a sump pit, and repouring concrete. It takes three to six days and requires no excavation outside.
Why most Toronto houses end up here
Not because it is better. Because digging is often impossible.
A large share of this city's housing is semi-detached and row stock on narrow lots, with shared walkways three or four feet wide, no rear access, and a neighbour's wall within arm's reach. You cannot get an excavator in, and hand digging a full perimeter to footing depth costs more than the house needs to spend.
Then there is everything sitting on top of the foundation — interlock, decks, steps, a driveway, thirty years of established garden. Removing and reinstating all of it frequently costs more than the waterproofing itself.
What a proper installation includes
The slab is cut and broken back roughly 12 to 18 inches from the wall, right down to the footing.
Perforated pipe is laid beside the footing — not on top of it — bedded in clear stone and wrapped in filter fabric so clay fines cannot silt it up.
A dimple membrane runs up the inside face of the wall and turns down into the stone bed, so any water coming through the wall is caught and directed into the drain rather than tracking across the floor.
The pipe falls to a sump pit, and a pump discharges it away from the house. Fresh concrete goes back over the trench.
The honest limitations
Two, and neither is a reason to avoid interior work — just to understand it.
First, the wall still gets wet. On a poured concrete foundation that is largely cosmetic. On a block foundation, water sitting in the cores over years produces efflorescence, spalling and eventually mortar deterioration. If your foundation is block and you can dig, exterior waterproofingis the more durable answer.
Second, you now depend on a pump. A sump pump is a mechanical device with a finite service life, and it fails during exactly the storm that needs it, often while the power is out. A battery backup at $300 to $800 is not optional on a system your dry basement depends on — seesump pump installation.
What it costs
| Work | Toronto 2026 range |
|---|---|
| Interior membrane and drain channel | $80 to $150 per linear foot |
| Full interior drainage system | $8,000 to $15,000 |
| Sump pump installed | $650 to $4,000 |
| Battery backup for the pump | $300 to $800 |
| Crack injection, per crack | $450 to $1,100 per crack |
One genuinely useful detail: the sump pump and its battery backup are covered by the City of Toronto Basement Flooding Protection Subsidy, up to $2,250 and $300 respectively. The interior waterproofing system they are attached to is not covered at all.