Flat roof in Montréal: white roof rules, membranes, permits

In Montréal, redoing a flat roof is about more than the membrane. Most boroughs require a white, highly reflective or green covering, and a permit to replace it. This guide summarizes the City of Montréal page Rénover un toit plat ou à faible pente (in French, updated February 2, 2026) and the City of Laval page on exterior home renovation (in French), both read on November 3, 2026. The rules change from one borough to the next: the City page shows those of your address once you pick your borough.

1. What counts as a flat roof?

The City’s page covers flat or low-slope roofs, meaning a slope under 2:12 (16.7%). Standards vary with the borough, the type of building and the nature of the work.

2. Maintenance without a permit, replacement with one

• Rosemont–La Petite-Patrie: no permit to maintain or repair (replacing a few shingles, adding tar); a permit to replace the covering of a flat roof.
• Saint-Laurent and LaSalle: same idea, but a permit is required as soon as the work touches the roof’s insulation or structure.
• Le Plateau-Mont-Royal: replacing the membrane needs no permit, except on a building with heritage status. A permit is needed to change the insulation or structure, for instance to change the slope, add mechanical equipment or skylights.

3. White roofs, SRI and green roofs: what the boroughs require

The solar reflectance index (SRI), shown on the manufacturer’s product sheet or, in several boroughs, by a professional’s opinion, is at the heart of the rules. The threshold varies: at least 66 in Ahuntsic-Cartierville, at least 78 in Rosemont–La Petite-Patrie, Verdun, Saint-Laurent and Le Sud-Ouest, at least 82 in Saint-Léonard for buildings other than single-family homes. In Rosemont–La Petite-Patrie, the allowed options are a white material, painted white or covered with a reflective coating or white gravel, a material with an SRI of at least 78, a green roof, or a combination; on a new building, tar and white gravel roofs are banned there. These requirements do not cover the part of the roof taken up by mechanical equipment (air conditioner, heat pump) or a deck.

On the Plateau, the minimum SRI of 56 (white or light grey) applies to new buildings, additions and changes of volume or slope. In Le Sud-Ouest, built-up roofs with asphalt and gravel remain allowed if the top layer is marble ballast or white gravel. For a green roof, several boroughs ask you to apply in person at the permit counter.

4. Elastomeric and TPO membranes: what the rules say

The City’s page does not rank membranes by brand or technique: it sets a result (colour or SRI). In LaSalle, for a flat roof under 300 m², the list of allowed new materials expressly names elastomeric membrane and thermoplastic polyolefin (TPO) membrane, alongside asphalt and gravel; above 300 m², a white material or one with an SRI of at least 56 is required. In Le Sud-Ouest, the quote filed with the application must describe the membrane and its colour, with the product sheet showing the SRI. Ask for both details in every quote: without them you can neither compare offers nor get the permit.

5. Fees, timelines and documents

In most boroughs, the review fee is $9.80 per $1,000 of work, on an estimated cost that must include plans, labour, equipment and taxes, with a minimum of $167.40 for a residential-only building; it is non-refundable. The documents usually requested include the quote or a cost estimate grid, the certificate of location and the product sheet showing the SRI. In Rosemont–La Petite-Patrie, the average review time is 2 to 4 weeks once the file is complete, and the page notes that an authorization from the Service de l’eau may be required for a lot with more than 1,000 m² of impervious surfaces. Villeray–Saint-Michel–Parc-Extension asks owners to wait for the permit before buying materials.

6. In Laval

According to the City of Laval, replacing the roof covering with the same material while adding insulation needs no permit; replacing it with a new material does. If a quote proposes a different type of roofing, plan for that step.

7. What Montréal’s permits show

In the City’s open permit data (in French), out of 20,621 permits issued from October 27, 2025 to October 26, 2026, 564 describe a white gravel or “white roof”, 349 an elastomeric membrane, 34 a TPO membrane and 20 a green or vegetated roof. Roofing falls under RBQ subclass 7 (insulation, waterproofing, roofing and exterior cladding): check the company’s licence. To find a roofer, see roofers in Montréal, in Saint-Léonard or in Laval, or describe your flat roof so licensed companies can reply. The directory prepares no quotes and picks no company for you. See also choosing a roofer and attic insulation.