Green and White Roofs in Montreal and Laval: The By-laws

Redoing a flat roof in Montreal or Laval is no longer a colour choice. In both cities, the list of permitted coverings is closed: white, vegetated or reflective. In Montreal, the figure required changes from one borough to the next; in Laval, it is the same everywhere. Here is what each city imposes, what the Régie du bâtiment du Québec demands before soil goes onto an existing frame, and what your insurer needs to know.

Montreal: a closed list of coverings for flat roofs

The city’s page “Rénover un toit plat ou à faible pente,” updated on February 2, 2026, starts with the threshold: a slope below 2:12, that is, 16.7%. Below that threshold, the only authorized coverings are a material that is white, painted white or covered with a reflective coating or white gravel, a material whose solar reflectance index reaches your borough’s threshold, a green roof, or a combination of those coverings.

So the by-law does not require you to plant anything. It requires you to reach an index and accepts a green roof as an equivalent.

The permit, on the other hand, depends on the address. In Anjou, no permit is needed to replace a flat roof, but the list of materials applies all the same. In Plateau-Mont-Royal and in Côte-des-Neiges and Notre-Dame-de-Grâce, replacing the membrane counts as maintenance, except for a heritage building. In Plateau-Mont-Royal, the materials list covers only new buildings, extensions and a change of volume or slope. In Pierrefonds-Roxboro and in Rivière-des-Prairies and Pointe-aux-Trembles, redoing an asphalt roof with an identical or similar material requires no permit. In Saint-Léonard, for a single family home, the authorized materials are those permitted by the building code.

Elsewhere, a permit is required to replace the covering, and the manufacturer’s technical sheet stating the index is one of the documents demanded. Review fee: $9.80 per $1,000 of work ($11 in Montréal-Nord), with a minimum of $167.40 for an exclusively residential building and $491.70 for a commercial or mixed building. For a vegetated roof, several boroughs require an application in person at the permit counter. Winter scheduling and permits are covered in winter renovation permits in Montreal and Laval.

The index required changes from one borough to the next

Two neighbouring streets in two different boroughs do not have the same list. Here is what the city’s page showed on October 31, 2026, unchanged since its February 2, 2026 update.

Several boroughs exclude the part of the roof taken up by mechanical equipment or a terrace. The page cites the Règlement d’urbanisme 01-274 and the Règlement sur la construction et la transformation de bâtiments 11-018 in the Ahuntsic-Cartierville entry; for any other address, the by-law involved is confirmed at the borough’s permit counter. For the rest of the climate adaptation work, see climate resilient renovations.

Laval: the urban planning code also requires white or green

Since November 11, 2022, Laval has applied its urban planning code (Code de l’urbanisme), by-law CDU-1, which replaced the old zoning by-law L-2000. Its section 380 is Laval’s counterpart to the Montreal list. A main or accessory building with a flat roof must carry one of the following coverings:

• a green roof;
• a material that is white, painted white or covered with a reflective coating or white ballast;
• a material with an SRI of at least 78, attested by the manufacturer’s specifications or by a professional’s specification;
• a combination of those coverings.

The code defines a flat roof as one with a slope of 16.7% (2:12) or less. Three exemptions: structures and equipment authorized on a roof, accessory buildings to a dwelling with a footprint under 40 m², and farm buildings. Unlike Montreal, the threshold is the same in every neighbourhood: 78.

The permit. Laval’s exterior residential renovation permit sheet separates two cases. Replacing the roof covering with the same material, and adding insulation, requires no permit. Replacing it with a new material requires one: stated processing time of 30 days, cost of $92 for the first $20,000 of work, plus $2.50 per $1,000 or part of $1,000. Going from a black membrane to a white one, or to a green roof, is precisely the case that triggers the permit. If the address is covered by a site planning and architectural integration program (PIIA), further requirements apply: the city’s Info-règlements tool shows this address by address.

No permit does not mean no rule. Section 2 of the code requires all work to comply with the by-law, permit or not. What happens to a black roof installed before November 11, 2022 and redone identically is a matter of acquired rights, covered in title 9 of the code: the city confirms it for a given address, before the materials are ordered.

New buildings. Section 141 adds a structural requirement: the frame of a flat roof must be designed to receive an extensive green roof, on top of the Construction Code loads, when the building has more than 3 storeys and the roof area exceeds 250 m².

For a Laval seller weighing a new roof against selling as is, renovating before selling in Laval compares the two options.

White roof, green roof, blue roof: three techniques, not three shades

The white roof is a covering. It changes nothing structurally and satisfies the by-law through its index.

The green roof is a system laid over the waterproofing. According to the environment ministry’s Guide de gestion des eaux pluviales, the studies reviewed give an average retention rate of 60%, in a range of 39 to 72%, a delay in peak flow of 20 to 40 minutes, and a reduction in runoff volume of 45 to 60%.

The blue roof is temporary water storage. The guide is clear about where it belongs: it applies above all to large flat industrial or commercial roofs, residential roofs usually being sloped. And about its effect: retention reduces the peak flow downstream, but the volume discharged to the sewer does not go down, since the discharge is spread over a longer period.

That last line counts: a blue roof does not exempt you from the index, retention not being a covering.

The load a green roof adds to an existing frame

The reference document is the guide from the Régie du bâtiment du Québec, Critères techniques visant la construction de toits végétalisés, updated in June 2015. Its basic conditions already rule out many buildings: noncombustible construction, a roof no more than 46 m above grade, a slope of no more than 17%, and a covering that is not of the multilayer, asphalt and gravel type. The fire department must be consulted from the planning stage on.

The weight. The guide requires the structure to be designed under part 4 of the Code taking into account the weight of a water saturated vegetated roof for every calculation, including seismic loads. Substrate density is determined under standard ASTM E2399-12 or, failing that, with an unfactored value of 2,000 kg/m³ for saturated density. The substrate must be at least 100 mm. The arithmetic is simple: 100 mm at that density is 200 kg per square metre, before the vegetation, before the snow and before the water held in the drainage layer. The real figure for your roof comes from the engineer, under standard ASTM E2397-11.

The calculation must also assume the worst: blocked drains, flooded substrate, water rising to the scuppers or overflows, whose accumulation the guide caps at 150 mm. To the live loads you add the snow that vegetation holds differently from a wind swept roof, and the substrate stored on site the day the membrane gets redone. The environment ministry’s guide says it among its limitations: the weight of the snow can restrict the application to roofs with sufficient load bearing capacity.

What Laval’s code takes over. For buildings exempted from the Building chapter of the Construction Code by its section 1.04, section 144 of Laval’s urban planning code takes over these requirements: calculations on the saturated substrate under standards ASTM E2397 and E2399, a density of 2,000 kg/m³ when no test is done, calculations by an engineer. It also sets three types of roof, extensive (0.1 to 0.15 m of substrate), semi-intensive (over 0.15 m and up to 0.3 m) and intensive (over 0.3 m), and allows an extensive roof on a building of combustible construction, with a fire separation of at least 45 minutes if the building is not sprinklered. A green roof section may not exceed 300 m² on a combustible building or 900 m² on a noncombustible one, nor 30 m in any dimension. A green roof is prohibited over shingles or tiles.

Permit, sealed plans and attestation: what the owner keeps

Two requirements in the RBQ guide answer the question everybody asks. All loads must be shown on plans and specifications bearing the seal and signature of an engineer. And for an existing building, structural resistance must be analyzed by an engineer, taking into account the new permanent load, the increased snow loads, rainwater accumulation and seismic behaviour. Part 10 of the Code, the one on alterations, applies.

The waterproofing must be verified before the plant cover goes down, by one of the six tests the guide lists, and the report is given to the owner, who must also obtain from the designer an attestation that the guide’s conditions have been met. In Laval, section 144 puts this waterproofing test on the owner, at the owner’s cost, before installation, and requires a water supply point and access to the roof.

Sealed plans, waterproofing report and attestation: that is what a buyer will ask for, and what the seller’s declaration leads them to question. The seller’s guide describes the rest of the file.

A limit to keep in mind: the RBQ guide governs buildings subject to the Code, and its first condition is noncombustible construction. A Montreal plex with a wood frame is not. What applies to your building gets verified with the Régie du bâtiment, the municipality and an engineer, not in an article.

What Montreal pays per square metre

The amounts grid of RénoPlex, Montreal’s renovation program for buildings of 1 to 5 dwellings, updated on August 18, 2026, has two lines for flat roofs:

The caps are $26,000 for a single family home and $52,000 for a building of 2 to 5 dwellings. Eligibility depends on the block of work the building qualifies for, and the amounts change from one update to the next: have yours confirmed before signing with a roofer.

In Laval, no municipal green roof grant was found. By-law L-13114, in force since June 10, 2024, subsidizes planted landscaping, but its text does not mention roofs.

Mandatory maintenance, and what the insurer has to know

Maintaining a green roof is not a good practice, it is a condition. The RBQ guide requires a program drawn up by a landscape architect or another specialist, given to the owner and recorded in a register kept on site, covering irrigation, fertilization, weeding, replanting and inspection of the edges, the drains, the flashing and the membrane. The mature vegetation cover must be maintained at 80% or more.

On the insurance side, the rule is in the Civil Code of Québec. Article 2466 requires the insured to promptly declare circumstances that aggravate the risk and result from the insured’s own acts, where they are of a nature to materially influence the premium, the assessment of the risk or the decision to continue the insurance. Article 2467 gives what follows: the informed insurer may cancel the policy or propose a new rate in writing, which the insured must accept and pay within 30 days, failing which the policy ceases to be in force.

The Bureau d’assurance du Canada puts “had the roof redone” on its list of changes to review at renewal. Two of its rules touch the green roof directly. The indemnity for the building is the cost of rebuilding in the same place with materials of the same kind and quality: a vegetated system must therefore sit inside the insured amount. And the insurer must have the damaged part repaired, not the whole roof redone. On a green roof, that means finding the leak under the substrate, then lifting it. The ministry’s guide notes it as a limitation: since water is encouraged to stay longer on the roof, faulty waterproofing becomes damaging.

No Bureau d’assurance du Canada publication consulted puts a figure on what a vegetated roof does to a premium. The files that become hard to place are described in a home that is hard to insure in Quebec.

What can be demonstrated, and what cannot

No official source consulted puts a figure on what a green roof or a white roof adds to the resale price of a Montreal or Laval plex. If a supplier announces a percentage of added value, ask for the study.

What can be documented is more modest. The National Research Council of Canada instrumented two large green roofs in Toronto and published its observations in 2005: green roofs reduce heat flow through the roof, which lowers energy demand for heating and cooling, whatever the roofing system, with greater efficiency in summer than in winter. Neither the NRC nor the ministry’s guide translates that into dollars on an electricity bill: do not budget a saving. For the membrane, the guide states a longer useful service life, thanks to protection against ultraviolet light and the impact of rain, without advancing a number of years. The particularities of a duplex flat roof are in the features of the Quebec house.

To go further, read the service life of a roof in Quebec and how to choose a renovation contractor.

Torn between redoing a flat roof with a white membrane and planting it before you sell? Write to me. We look at the index required at your address, in Montreal or Laval, and at the documents the buyer will ask you for.

Georges Matar

Residential Real Estate Broker · RE/MAX DU CARTIER INC.

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