The Ontario Building Code | Dampproofing of Floors-on-Ground
220.127.116.11. Dampproofing of floors-on-Ground
(1) Where floors are dampproofed, the dampproofing shall be installed below the floor, except that where a separate floor is provided over a slab, the dampproofing is permitted to be applied to the top of the slab.
(2) Where installed below the floor, dampproofing membranes shall consist of polyethylene not less than 0.15 mm thick, or Type S roll roofing.
(3) Joints in dampproofing membranes described in Sentence (2) shall be lapped not less than 100 mm.
(4) Where installed above the slab, dampproofing shall consist of,
(a) no fewer than 2 mopped-on coats of bitumen,
(b) not less than 0.05 mm polyethylene, or
(c) other material providing equivalent performance.