← Ontario Building Code FAQ
OBC DIVISION B · PART 9 · SECTION 9.13 — DAMPPROOFING, WATERPROOFING AND SOIL GAS CONTROL

When is waterproofing required instead of dampproofing for a foundation in Ontario?

Dampproofing is the default for below-grade foundation walls and floors in Ontario. Full waterproofing is required where hydrostatic pressure exists, meaning the water table can rise against the wall or slab and push water through the assembly.

Code reference
The OBC requires below-grade walls and floors-on-ground to be dampproofed where they enclose interior space and are not subject to hydrostatic pressure. Where groundwater can create hydrostatic pressure against the foundation, the walls and floor must instead be waterproofed with a membrane system designed to resist water under pressure.
OBC Division B, Subsections 9.13.2. and 9.13.3.

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

On most Ontario sites with decent drainage and a water table below the footing, spray or trowel dampproofing plus weeping tile is sufficient. Waterproofing becomes mandatory on high-water-table or poorly drained sites, and it is a different scope: membrane systems lapped and sealed, often with drainage board and floor-slab protection. Builders commonly discover this at excavation, so a soils report or local knowledge before pricing avoids expensive change orders. Drainage under 9.14 works together with this requirement.

Plain language

If your lot drains well, a basic black coating on the outside of the basement wall usually does the job. If groundwater can actually press against your basement, the code requires a true waterproofing membrane instead, which is a bigger, costlier system.

Related questions

What are the radon and soil gas control requirements for new houses in Ontario?Does foundation dampproofing go on the inside or outside of the wall in Ontario?

Get answers like this for any code question

BUILDAiD Assist searches the building code and answers in plain English with exact citations — in seconds.

Try BUILDAiD Beta

This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.