Question 1

Does Ontario's Code require dampproofing under a basement slab?

Accepted Answer

Yes, with three exceptions. Ontario's Building Code says floors-on-ground shall be dampproofed (9.13.2.1). The exceptions are floors in garages, floors in unenclosed portions of buildings, and floors installed over granular fill that meets 9.16.2.1, which is the layer of at least 100 mm of coarse clean granular material under a floor-on-ground.

Question 2

Does a waterproofed Ottawa wall also need dampproofing?

Accepted Answer

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.

Question 3

Must a block foundation in Ottawa be parged before a membrane goes on?

Accepted Answer

Yes. Ontario's Building Code requires at least 6 mm of mortar parging on the exterior face of a masonry wall below ground, coved over the footing, before dampproofing or waterproofing is applied (clauses 9.13.2.3 and 9.13.3.3). That requirement applies to block foundations specifically; poured concrete walls have a different rule, which is that holes and recesses must be sealed before the membrane goes on.

Question 4

Can waterproofing replace the drainage layer on an Ottawa foundation?

Accepted Answer

In one specific sense, yes. Ontario's Building Code calls for a drainage layer only where foundation-wall insulation extends more than 900 mm below the ground outside, and says that layer is not required where the wall is waterproofed. But the drainage layer is not the drain tile, and the wall still needs drainage at its base whether or not it is waterproofed.

Dampproofing vs Waterproofing

Does Ontario's Code require dampproofing under a basement slab?

Does a waterproofed Ottawa wall also need dampproofing?

Must a block foundation in Ottawa be parged before a membrane goes on?

Can waterproofing replace the drainage layer on an Ottawa foundation?