Flat roof in Fabreville

Where the question comes up

In its land use plan, the City writes that the neighbourhood includes multi-family buildings along boulevard Dagenais Ouest. The City does not describe the roofs of these buildings.

The City's heritage inventory gives a single figure: of the 18 principal buildings it lists in Fabreville, only one has a flat roof. This survey covers heritage buildings only and does not measure the neighbourhood. The page on roofing in Fabreville gives the portrait of the neighbourhood.

A "flat" roof can slope

The Code de l'urbanisme (Laval's urban planning code) defines a flat roof by a number: a slope of 16.7% or less, which is 2:12. Above that, the roof is sloped.

The definition matters for a house. A rear extension or an attached garage sometimes has a roof much less steep than the house's. If the slope of that part does not exceed 2:12, it is a flat roof under the Code, even if covered with shingles. We can measure the slope during our visit.

Article 380, in brief

For flat roofs, article 380 requires a green roof, a white covering or a material with a solar reflectance index of at least 78, and the Code does not say what applies to an existing roof redone identically. The details are on the area page.

Two points concern a homeowner.

• The article covers principal and accessory buildings. The text does not exclude the flat part of a house.
• It makes an exception for a residential accessory building with a footprint under 40 m².

For a small dark low-slope roof, the doubt is real. Redoing it with the same material does not require a permit for a residence, but the Code points out that an exemption from a permit is not an exemption from complying with the regulations. A written answer from the Service de l'urbanisme (urban planning department), obtained before the work, settles the question.

Coverings allowed on a flat roof

Article 379 of the Code names the roof coverings allowed in Laval. The following are used on a flat roof:

• TPO or EPDM membrane
• multi-ply tar membrane or elastomeric membrane
• heat-welded or self-adhesive membrane
• gravel, on an authorized membrane
• green roofing with its waterproofing membrane

On a low slope, water drains slowly, and a roofer often proposes a membrane rather than shingles. Replacing shingles with a membrane this way looks like a change of material, which requires a permit for a residence. The City does not define what same material means. Have the Service de l'urbanisme confirm it.

If you own a flat-roofed building

Ask us for the membrane's technical data sheet with the quote. The reflectance index required by the Code is confirmed by the manufacturer's specifications or by a professional's specifications.

Do not go up on the roof, even a flat one. From the top-floor units, note the stains on the ceiling and their date.

Frequently asked questions