Does a waterproofed Ottawa wall also need dampproofing?

No. Ontario's Building Code states that dampproofing is not required where the wall is waterproofed. The two are alternatives, not layers stacked on top of each other.

The distinction matters because the Code sets different thresholds for each. Dampproofing is required under clause 9.13.2.1 where finished ground outside sits higher than the ground level inside the foundation walls. Waterproofing is required under clause 9.13.3.1 where hydrostatic pressure occurs. The Code gives no number or test for when hydrostatic pressure occurs, so that determination belongs to the contractor who looks at the site, not to the Code itself.

Where waterproofing is used, clause 9.13.3.4 says it must be continuous across joints and at junctions, and protected from damage during backfilling. For a masonry block wall, clause 9.13.3.3 requires at least 6 mm of mortar parging on the exterior face below ground, coved over the footing, before the waterproofing goes on. For a poured concrete wall, holes and recesses are sealed first.

One thing waterproofing does not replace is the drainage at the bottom of the wall. Clause 9.14.2.1 requires drainage at the bottom of every foundation wall that encloses the building interior, unless it can be shown to be unnecessary. That requirement stands whether the wall is dampproofed or waterproofed. What waterproofing does remove is the drainage layer against the outside face of the wall, which the Code calls for only where foundation-wall insulation extends more than 900 mm below grade; it is a separate element from the drain tile at the footing.

When you are getting a quote for exterior work, ask the contractor to name in writing whether the scope is dampproofing or waterproofing, which clause of the Building Code applies to your wall, whether the drain tile is being replaced and where it discharges, and how the membrane is protected before backfill goes in.

To hear from Ottawa contractors directly, use the request form on this site, which sends your details to local waterproofing contractors listed in the Ottawa Construction Network directory.