Attic insulation in Québec: air sealing, venting, rebates

The attic is often where a house loses the most heat. Adding insulation up there is fairly simple work, but three things make the difference: air sealing, ventilation and what is already in place. Done right, it makes the upstairs rooms more comfortable and cuts down on ice dams.

1. Signs of a poorly insulated attic

• Icicles and ice dams along the roof edge.
• Snow on your roof melts faster than on the neighbours’.
• Frost or mould under the roof deck in winter.
• Cold rooms under the roof and rising heating bills.

2. Air sealing comes first

Warm, moist air from the house rises through recessed lights, the attic hatch, wires, the plumbing stack and ducts. These openings must be sealed before insulation goes in: otherwise moisture condenses under the deck and the insulation loses effectiveness. Our guide on caulking and weatherstripping shows where to look for those leaks.

3. Ventilation

The attic has to stay cold and dry. Baffles at the eaves keep an air channel open between the soffits and the upper vents, even under a thick layer of blown insulation. Ask the contractor how they plan it, and whether they check that the bathroom fan exhausts outdoors rather than into the attic.

4. Watch out for vermiculite

Grey-brown or golden pebble-like insulation in an older house may be vermiculite containing asbestos. Do not touch or move it: have it tested and have a specialized company remove it before any other work. Our guide on asbestos and vermiculite covers the precautions.

5. Permits and rebates in Greater Montréal in 2026

Insulating an existing attic rarely needs a permit, but check. In Boisbriand, insulating attics and exterior walls needs no permit, although standards still apply (construction, renovation or demolition, in French). In Laval, redoing the roof covering with the same material while adding insulation needs none either (exterior home renovation, in French). In Montréal, work that touches the insulation or the structure of a flat roof needs a permit, even where plain maintenance is exempt (City page, in French).

On the funding side, the Rénoclimat program changed on October 1, 2026. According to the page on what is new in the program (in French, updated October 13, 2026, read on November 1, 2026):

• the pre-work energy evaluation is no longer mandatory, but it is recommended;
• roof insulation can qualify for up to $2,000 for a single-family house and up to $5,000 for a duplex, a triplex or a multi-unit residential building;
• only a contractor holding the appropriate licences can do the eligible work, and that contractor fills out and signs the compliance form;
• the online portal for applications was still being built: keep your invoices and that form.

Hydro-Québec also lists roof insulation and caulking work among the LogisVert measures (in French). Read each program’s conditions before you sign the contract.

6. The quote and the licence

• The type of insulation (cellulose, blown wool or other), the thickness and the target insulation value.
• Air sealing, the baffles, and insulating and weatherstripping the attic hatch.
• Removal of the old insulation if needed, and the clean-up.

Insulation is part of RBQ subclass 7: look up the company’s licence before you sign, especially if you are counting on Rénoclimat. To find who does this work near you, see renovation in Montréal, in Boisbriand or in Repentigny, or describe your insulation project and get quotes. See also roof snow and ice dams.