Flat roof in Duvernay

What the City says, and does not say, about flat roofs

The land use plan says that detached single-family housing dominates the landscape of the hub, and it places a 1960s commercial core on boulevard de la Concorde Est. It does not describe the roofs.

The architectural heritage inventory gives a single figure: of the 50 main buildings it lists in Duvernay, 10 have a flat roof. This figure applies only to heritage buildings. Only one thing can be drawn from it: roofing in Duvernay can include a flat roof.

The 2:12 limit

The Code defines a flat roof as a roof with a slope of 16.7% or less, which is also written 2:12. Above this slope, the roof is called sloped.

At 2:12, the roof rises two units for every twelve units horizontally. An owner can have a roof that the Code classes as flat without ever having called it that. In the trade, these low slopes are often found on an extension, an attached garage or a carport: this is a general observation, not a fact recorded in Duvernay.

Do not measure the slope yourself. Ask us to write it in the quote, for each section of the roof.

What article 380 changes for these roofs

For a flat roof, article 380 of the Code requires a green roof, a white covering or a material with a solar reflectance index of at least 78, and it does not specify what applies to an existing roof redone identically.

This reservation matters for a house with a single low-slope section. Before covering it with the same dark membrane, ask the Service de l'urbanisme (the City's urban planning department) what it expects.

Small accessory buildings

Article 380 covers main buildings and accessory buildings. It makes an exception for a residential accessory building with a footprint of less than 40 m².

For a shed or a detached garage, the footprint is the first thing to know. If the building is close to this limit, let the Service de l'urbanisme say which side it falls on.

The membranes the Code allows

Article 379 lists the roof coverings allowed in Laval. On a flat or low-slope roof, quotes often propose one of these:

• a TPO or EPDM membrane
• an elastomeric membrane, in modified bitumen
• a multi-ply tar membrane, which gravel can cover
• a heat-welded or self-adhesive membrane

This list says what is allowed as a material. On a flat roof, article 380 adds requirements for colour or index.

For a residence, the City requires a permit when the material is new. The City does not define what same material means: switching from one of these coverings to another may count as a change, and it is up to the Service de l'urbanisme to say so.

What you can observe

Do not climb on the roof. From an upstairs window that overlooks the low-slope section, check whether water stays there after rain. Inside, photograph the stains on the ceiling under that section.

Frequently asked questions