Foundation Waterproofing

Foundation waterproofing is the definitive solution for GTA basements that leak — and in a region where the majority of homes have below-grade living space and clay-heavy soils that hold water against foundation walls, it is one of the most frequently needed exterior repairs. Ontario Building Code Section 9.13 establishes requirements for below-grade waterproofing that go beyond simple dampproofing: waterproofing must provide a continuous, impervious barrier that bridges cracks and resists hydrostatic pressure, whereas dampproofing only slows moisture vapour transmission through the foundation wall. The distinction matters because GTA soils — particularly the heavy clay tills found across Mississauga, Brampton, Vaughan, and much of Toronto — retain water after rainfall and snowmelt, creating sustained hydrostatic pressure against foundation walls that dampproofing alone cannot withstand. Exterior waterproofing involves excavating to the foundation footing, cleaning and preparing the wall surface, applying a waterproofing membrane, installing drainage board to protect the membrane and provide a drainage path, and installing or replacing the weeping tile (perimeter drain) at the footing level. The membrane itself is typically a cold-applied rubberized asphalt or polymer-modified asphalt product that remains flexible at GTA winter temperatures and bridges hairline cracks that develop as the foundation settles. Self-adhering sheet membranes are an alternative that provides consistent thickness and factory-controlled quality. Both systems require a continuous, lapped application from the footing to above finished grade, with careful detailing at corners, wall penetrations (water lines, sewer connections, electrical), and the footing-to-wall joint where the majority of basement leaks originate. Weeping tile — the perforated pipe at the base of the foundation that collects groundwater and directs it to the storm sewer, sump pit, or daylight outlet — is a critical component that fails over time. Original clay tile weeping systems on pre-1970 GTA homes are frequently collapsed, clogged with silt and root intrusion, or completely non-functional. Modern weeping tile uses 4-inch perforated PVC or corrugated HDPE pipe wrapped in filter fabric, bedded in clear gravel, and connected to a reliable discharge point. Interior crack injection — injecting polyurethane or epoxy resin into foundation wall cracks from inside the basement — provides a less invasive solution for isolated crack leaks, though it does not address exterior soil drainage or deteriorated weeping tile. Foundation waterproofing across the GTA typically costs $3,000 to $12,000 depending on the length of wall excavated, depth of excavation, soil conditions, weeping tile replacement scope, and whether the project requires shoring or underpinning adjacent structures on tight urban lots.

Find a Parging Contractor