How big must foundation drain tile be under Ontario's Building Code?

Ontario's Building Code requires foundation drain tile or pipe to be at least 100 mm in diameter (clause 9.14.3.2).

The pipe is laid so its top sits below the bottom of the floor slab. Butt joints are left open between 6 mm and 10 mm. The pipe must be covered on the top and sides with at least 150 mm of crushed stone or other coarse clean granular material, where no more than 10 per cent of the material passes a 4 mm sieve (clause 9.14.3.3). The Code also sets out an alternative: a granular layer at least 125 mm deep under the footing, extending at least 300 mm beyond its outside edge (clause 9.14.4.2).

Where the drain tile goes matters too. The Code says foundation drains discharge to a sewer, a drainage ditch, or a dry well (clause 9.14.5.1). A dry well is only permitted where natural groundwater sits below its bottom, and it must be at least 5 m from the foundation. The City of Ottawa notes that in some older homes the foundation drain may connect to the sanitary or combined sewer, or may not be present at all, and that foundation drains should not be connected to the sanitary sewer.

One thing worth knowing: the Code requires drainage at the bottom of every foundation wall that encloses the building interior, unless it can be shown to be unnecessary (clause 9.14.2.1). Replacing drain tile is on the City of Ottawa's permit list, so a building permit is required before that work starts. Ask the contractor who pulls the permit and confirm that the new tile's discharge point complies with both the Code and the City's requirements.

A fair quote for drain tile work should spell out the pipe diameter, the type and depth of granular cover, where the drain discharges, and whether any interior or exterior membrane work is included in the scope.

If you want to hear from Ottawa waterproofing contractors directly, the request form on this site sends your details to contractors listed in the Ottawa Construction Network directory.