Blog
25 May 2026
On a flat roof, the entire waterproofing of the building relies on the membrane. In Montreal, SBS modified bitumen elastomeric membrane is a system commonly used on apartment buildings, plexes and commercial buildings. Understanding what it is made of and how it is installed helps you better assess the condition of a roof and the work being proposed.
This article explains what an elastomeric membrane SBS, how a two-ply system works, what installation methods exist and how to maintain it so it protects the building as long as possible.
An elastomeric membrane is a roll of bitumen with an added polymer, SBS (styrene-butadiene-styrene), around a reinforcement, usually polyester or fibreglass. The bitumen provides the waterproofing. The polymer gives it elasticity, which allows the membrane to follow the building’s movements instead of splitting.
This flexibility is valuable in Quebec. Between winter and summer, and sometimes from one day to the next in spring, the roof expands and contracts. Freeze-thaw cycles, snow and UV rays stress the surface all year round. A membrane that stays flexible in cold weather stands up better to these stresses.
SBS modified bitumen has another advantage: it lends itself well to localized repairs and resurfacing. A damaged section can often be redone without touching the rest of the roof, provided the surrounding membrane is still sound.
An elastomeric roofing is not made of a single sheet. It is a two-ply system: two membranes laid one on top of the other, overlapped and offset so that their seams never fall in the same place.
The first membrane, called the base sheet, is fastened or bonded to the substrate. It forms a first continuous barrier against water. It also receives the first waterproofing details around roof drains, vents and equipment bases.
The second membrane, the cap sheet, covers the base sheet. Its surface is protected by mineral granules that reduce the effect of UV rays and weather-related wear. Bonded together, the two layers form redundant waterproofing: if the surface is damaged in one spot, the base sheet continues to protect the building.
The most delicate areas of a flat roof are rarely in the middle. They are the upstands along parapets and walls, the roof drains, ventilation ducts and mechanical equipment supports. The care given to these details weighs heavily on the service life of the whole system.
There are several ways to install an elastomeric membrane. The choice depends on the building, the existing substrate, the insulation and the job site environment.
With this method, the installer heats the underside of the membrane with a torch to weld it to the substrate or the base sheet. The melted bitumen creates a continuous bond between the layers and at the overlaps. This technique requires experience and strict fire precautions.
Some membranes are self-adhered: they bond without a flame. This option is useful near combustible materials, on certain substrates or when you want to limit torch use. A single system can also combine a self-adhered base sheet with a torch-applied cap sheet.
Toitures OBM installs Soprema systems, including the mechanically fastened conventional system and the self-adhered conventional system. In a conventional system, the membrane is installed over the insulation. The mechanically fastened version secures the components to the roof deck with fasteners, while the self-adhered version relies on the adhesion of the membranes.
A properly installed and regularly maintained elastomeric membrane can protect a building for several decades. Its actual lifespan depends on several factors: installation quality, the condition of the substrate, water drainage, sun exposure and how often it is inspected.
Water pooling near a clogged roof drain, an upstand coming loose or granules disappearing in places are signs to watch for. Corrected early, these problems can often be solved with a localized repair. Left alone, they can lead to leaks and more extensive work.
Depending on the condition of the membrane, several options are possible. Flat roof repair targets a localized leak, a crack, a loose section or resealing around a roof drain or penetration. Resurfacing involves cleaning and preparing the existing membrane, then applying a cap sheet. A complete roof replacement replaces the system when the membrane reaches the end of its service life.
Toitures OBM assesses the condition of the roof and the needs of the building before recommending any of these options, to avoid unnecessary work. Its recommendations are clearly explained to the owner.
Regular inspection is the simplest way to extend the life of a flat roof. During a maintenance and inspection visit, the team checks, among other things:
A spring inspection shows the effects of winter, and another in the fall helps prepare the roof before the snow.
Toitures OBM is based at 1215 rue Tellier in Laval and installs elastomeric membrane flat roofs in Montreal, Laval and on the North Shore. The company is Soprema PAQ+S certified, CAA-Québec Recommended and holds RBQ licence 5778-2823-01.
Its services include elastomeric roof replacement, new flat roof construction, repair, resurfacing, and maintenance and inspection. It works on commercial, industrial and multi-unit buildings, as well as on residential flat roofs. The team can be reached Monday to Friday, from 8 a.m. to 5 p.m., and financing is available through Financeit.
Yes. Self-adhered membranes make it possible to install a system without a flame, in whole or in part. The choice depends on the substrate, the insulation and the building’s constraints.
The two-ply system layers a base sheet and a cap sheet with offset seams. This redundancy reduces the risk of water infiltration if the surface is damaged in one spot.
Check with your municipality before work begins.
Whether your flat roof needs an inspection, a repair or a complete roof replacement, an on-site assessment shows where the membrane stands. Contact the Toitures OBM team at 514-449-5469 or fill out the form to get a free quote.
OBM Roofing
Elastomeric membrane specialists for commercial, industrial and multi-unit buildings in Laval, Montreal and the North Shore.
