Why Flat Roofs Require a Different System Than Pitched Roofs
Flat and low-slope roofs cannot use asphalt shingles because shingles rely on gravity and slope to drain water. A flat roof — typically defined as having less than a 3:12 pitch — requires a continuous, waterproof membrane system that forms a sealed barrier across the entire surface, including at seams and penetrations.
In Quebec, the building code and local climate conditions make elastomeric SBS modified bitumen membrane the most common and best-validated flat roofing solution for both residential and commercial applications.
What Is SBS Elastomeric Membrane?
SBS modified bitumen is a roofing membrane composed of bitumen (asphalt) reinforced with a fibreglass or polyester mat and modified with styrene-butadiene-styrene polymer. The polymer modification gives the membrane its elastomeric properties — meaning it stretches and recovers rather than cracking under thermal stress.
In Gatineau’s climate, where surface temperatures can range from -30°C in January to +60°C on a summer rooftop, a roofing membrane must be able to expand and contract without failing at the seams. SBS membranes are specifically engineered for this.
Application method: Torch-welded (heat-applied) or self-adhesive. Torch welding requires certified technicians — Cossette roofers hold the required certifications under Quebec law.
Lifespan: 35 to 40 years for a properly installed two-layer system.
Layers: A base layer (base ply) bonded to the roof deck, topped by a granulated cap sheet that provides UV and impact protection.
Residential Flat Roofs in Gatineau: Where Elastomeric Membrane Is Used
Many homes in Gatineau, Hull, and Aylmer were built with flat or low-slope roof sections — often over attached garages, rear additions, enclosed porches, or sunrooms. Signs that a residential flat roof needs attention include: visible cracking, blistering, or separation at the membrane seams; water stains on ceilings or interior walls; ponding water more than 48 hours after rain; soft or spongy spots when walking on the roof deck; or a membrane that is 20 or more years old.
The Cossette Flat Roofing Installation Process
Cossette Roofing follows a structured installation process: free inspection and evaluation; complete tear-off of old membrane and insulation where required; repair or replacement of damaged deck sections; installation of rigid insulation board where specified; torch application of SBS base layer; torch application of granulated SBS cap sheet with full overlap at all seams; flashing installation at all penetrations, walls, and parapet transitions; and final inspection with warranty documentation.
Frequently Asked Questions
How much does a flat roof cost in Gatineau?
Flat roof pricing depends on surface area, layers being removed, deck condition, and whether additional insulation is required. Cossette provides free, detailed written estimates for all flat roofing projects. Call 819-777-7177 or visit our website to request yours.
Can elastomeric membrane be repaired instead of replaced?
Yes, in many cases. If the membrane is less than 20 years old and the damage is localized, Cossette can perform targeted repairs that restore waterproofing without a full replacement. A professional inspection is required to determine whether repair or replacement is the more cost-effective path.
Is elastomeric membrane the same as EPDM or TPO?
No. EPDM and TPO are different flat roofing systems used more commonly in the United States and in large commercial applications. SBS elastomeric membrane is the dominant system in Quebec and has a long track record in Gatineau’s freeze-thaw climate. Cossette also installs TPO membranes for commercial applications where specified.