Blog
24 August 2026
Elastomeric membrane is one of the most widely used waterproofing systems on flat roofs in Quebec. Made of SBS modified bitumen and installed in two layers, it stays flexible in the cold and forms a continuous barrier against water. Like any material exposed to the weather, however, it eventually wears out. In Montréal-Nord, where there are many plexes, apartment buildings and commercial buildings with flat roofs, recognizing the signs of wear early helps limit damage and avoid more extensive work.
Several factors weaken a membrane over the years. Quebec’s freeze-thaw cycles are among the most demanding: water seeps into micro-cracks, freezes, expands and gradually widens the openings. After a few winters, a small weakness can become a point of water infiltration.
UV rays also play a role. Summer after summer, they dry out the surface of the membrane, which loses flexibility and becomes more prone to cracking. The granulated cap sheet protects the membrane, but it wears too, especially where the granules have come off.
Other causes come up often:
A look at the roof often gives good clues. Blisters, lifting seams, loose sections, surface cracks or areas where the granules have disappeared indicate that the membrane is no longer fully doing its job. Puddles that remain several days after rain also deserve attention, since they speed up membrane wear in that spot.
Inside, rings and brownish stains on the ceiling, blistering paint or a persistent musty smell are signals to take seriously. Moisture attacks the insulation and the structure, and it can affect indoor air quality.
The longer the work is put off, the more the damage is likely to spread. A localized repair done in time can often postpone a complete roof replacement.
A lasting repair starts with a good understanding of the problem. Water can travel under the membrane or along the structure before appearing inside, so the stain on the ceiling is not always located under the damaged area.
The roofer examines the entire roof: overall condition of the membrane, seams, upstands, penetrations, roof drains and water drainage. This overview determines whether a localized repair is enough or whether the condition of the membrane calls for another solution, such as resurfacing or roof replacement.
The damaged area is cleaned, loose or damaged sections are removed and the substrate is dried. A clean, dry surface is essential for the new membrane to bond properly to the old one.
The patch of SBS modified bitumen membrane is then torch-applied or, depending on the case, installed as a self-adhered membrane. Overlaps and seams are carefully treated, then the surface receives a granulated finish that protects the repair from UV rays. Around roof drains and penetrations, the waterproofing is fully redone, since this is often where leaks start.
Not every worn membrane calls for the same solution. When the damage is limited to a few areas and the rest of the membrane is in good condition, a targeted repair is generally the most sensible option. If the membrane is sound but its surface is worn, resurfacing (cleaning, preparing the existing membrane and adding a new cap sheet) can extend its service life. When leaks multiply or the insulation is waterlogged, replacing the elastomeric roofing becomes the more logical choice.
The choice is based on the actual condition of the roof, not on a one-size-fits-all rule. The goal is to fix the problem at the source without doing unnecessary work.
Regular inspection, ideally in spring after the snowmelt and in fall before winter, makes it possible to spot small issues before they get worse. Cleaning the roof drains is a simple step that greatly reduces the risk of standing water. With regular maintenance, an elastomeric membrane can protect a building for several decades.
Toitures OBM is a roofer specializing in elastomeric membrane flat roofs, based at 1215 rue Tellier in Laval. The team works in Montréal-Nord as well as the rest of Montreal, including Ahuntsic-Cartierville and Anjou, and in Laval and on the North Shore. Its services include flat roof repair, resurfacing, maintenance and inspection, elastomeric roof replacement and new flat roof construction, for commercial, industrial and multi-unit buildings as well as residential flat roofs.
Toitures OBM installs Soprema systems, is Soprema PAQ+S certified and CAA-Québec Recommended, and holds RBQ licence 5778-2823-01. Before recommending anything, the team assesses the condition of the roof and the needs of the building, then explains its recommendations clearly. Financing is also available through Financeit.
A repair requires a clean, dry surface. Snow, ice and moisture make the work more difficult. Depending on the condition of the roof and the weather, it is sometimes better to schedule the repair for a more favourable time. An inspection shows what can be done and helps limit damage in the meantime.
It depends on the condition of the rest of the membrane. If it is still flexible and well bonded, a targeted repair may be enough. If cracks and separations multiply, successive repairs end up costing more than a lasting solution, such as a roof replacement.
On a flat roof, water that gets under the membrane can travel along the roof deck or through the insulation before coming through the ceiling. That is why the roofer inspects the whole roof, especially the roof drains, upstands and penetrations, rather than only the area above the stain.
An elastomeric membrane showing signs of wear deserves prompt attention. To have your flat roof inspected in Montréal-Nord, contact the Toitures OBM team at 514-449-5469, Monday to Friday from 8 a.m. to 5 p.m., or request a free quote.
OBM Roofing
Elastomeric membrane specialists for commercial, industrial and multi-unit buildings in Laval, Montreal and the North Shore.
