What Laval calls a flat roof
The Code gives a numerical definition: a flat roof has a slope of 16.7% or less, which corresponds to 2:12. Above that, the roof is considered sloped. A low-slope roof that looks tilted can count as flat.
The City describes apartment buildings and commercial buildings in the area. For their owners, this article is the starting point of any project involving roofing in Chomedey.
The four options in article 380
According to the Code, main and accessory buildings with a flat roof must have one of the following coverings:
- a green roof
- a white material, or a material painted white or covered with a reflective coating or white ballast
- a material with a solar reflectance index of at least 78
- a combination of these coverings
For the third option, the index must be shown by the manufacturer's specifications or a professional's specifications. Ask us to attach the membrane's technical data sheet to the quote, with the index clearly visible.
The article provides three exceptions: buildings and equipment that the Code allows on a roof, accessory buildings of a dwelling with a footprint under 40 m², and farm buildings.
The membranes the Code allows
Article 379 lists the roof coverings permitted in Laval. For a flat roof, the list includes:
- TPO or EPDM membrane
- materials certified as white roofing material
- multi-ply tar membrane and elastomeric membrane, in modified bitumen
- heat-welded or self-adhesive membrane
- gravel, laid over a permitted membrane
- green roofing, with its waterproofing membrane
The list says which materials are permitted. Article 380 adds a requirement for colour or index. An elastomeric membrane is permitted, but on a flat roof it must also meet one of the four options.
What the Code does not say
Article 380 states that buildings with a flat roof must have one of these coverings. It mentions neither new construction nor roof replacement. The text does not say whether the owner of a Chomedey building with a dark roof can redo it exactly as before.
According to the City's page, replacing the covering of a residence with the same material requires no permit. The project then involves no application to the City. The Code points out, however, that being exempt from a permit does not exempt anyone from complying with the regulations.
In that case, it is best to get a written answer from the Service de l'urbanisme (the City's planning department) before ordering the membrane. Its counter is at 1333, boulevard Chomedey, by appointment.
When a permit is needed
For the permit, the City does not look at the shape of the roof. It looks at whether the new covering is the same material as the old one: if so, no permit, otherwise one is needed. The fees and processing time are on the area page.
The City does not define what it means by the same material. Going from tar and gravel to a white membrane looks like a change, but it is up to the Service de l'urbanisme to say. Ask us to state in the quote whether the material changes and who handles the application.
What you can observe without climbing up
Do not climb onto the roof, even a flat one. From the top unit, note where the rings on the ceiling are. If a higher window looks onto the roof, check whether water sits there after rain.
Frequently asked questions
What reflectance index does Laval require for a flat roof?
The solar reflectance index must be at least 78, according to article 380 of the Code de l'urbanisme. This index must be shown by the manufacturer's specifications or a professional's specifications. A green roof or a white covering also meets the article.
Can I redo my flat roof with the same dark membrane?
The Code does not say. It requires a green, white or reflective covering for flat roofs, without saying what applies to an existing roof. Ask the Service de l'urbanisme before the work.
Is gravel allowed on a flat roof in Laval?
The Code allows gravel that covers a permitted membrane. To meet article 380, it names white ballast among the accepted coverings.
Does a shed with a flat roof count?
A small shed with a flat roof does not count. Article 380 makes an exception for an accessory building of a dwelling with a footprint under 40 m².