Blog
16 March 2026
On a commercial building, the flat roof protects much more than the structure: it protects inventory, equipment, tenants and business continuity. In Montreal, owners and managers of commercial buildings deal with snow, freeze-thaw cycles and UV rays, which put stress on the roof all year round.
Here is what you need to know to properly manage a commercial flat roof: the membrane system, water drainage, the roof assembly, maintenance and work planning.
A commercial roof often has a large surface, many penetrations and mechanical equipment installed directly on the membrane. Each of these elements is a point to watch.
The larger the roof, the farther water must travel before reaching a roof drain. Insufficient slope or a clogged roof drain can create areas of ponding water that put stress on the membrane.
Air conditioning units, ventilation ducts, vents and various supports pass through the membrane or rest on it. The connections around these elements are sensitive spots, where leaks often begin.
The technicians who service the equipment walk on the roof several times a year. Their repeated foot traffic wears down the membrane, especially near mechanical units and along the paths leading to them.
Toitures OBM specializes in elastomeric membrane flat roofs: a two-ply system of SBS modified bitumen membranes, torch-applied or self-adhered.
The base sheet forms a first continuous barrier, and the granulated cap sheet protects it from UV rays and the weather. The staggered seams of the two plies reduce the risk of leaks. Thanks to the SBS polymer, the membrane stays flexible and follows the building’s movements during temperature swings.
Toitures OBM installs Soprema systems, such as the conventional mechanically fastened system and the conventional self-adhered system. The choice takes into account the roof deck, the existing insulation and the building’s constraints, for example ongoing activities under the roof during the work.
On a commercial flat roof, water must be directed efficiently toward the roof drains. Standing water puts stress on the membrane and, in winter, can freeze around the roof drains. A few elements make the difference:
During a roof replacement, the slope and the roof drain connections can be reviewed to correct areas where water builds up.
Under the membrane, the insulation limits the building’s heat loss. A vapour barrier, installed under the insulation, reduces the passage of indoor moisture into the roof and the risk of condensation in the assembly.
When insulation is soaked by a leak, it loses its effectiveness and may need to be replaced during the work. This is one of the reasons why a leak on a commercial roof should be corrected quickly: the longer water gets in, the more the affected area is likely to spread.
A maintenance and inspection program helps you plan work ahead rather than react to it. The Toitures OBM team checks the roof drains and water drainage, the seams, the upstands and the penetrations, as well as the general condition of the membrane, and cleans the roof drains.
The inspection shows the effects of winter on the membrane, the upstands and the connections around the equipment.
Cleaning the roof drains and correcting small weaknesses prepare the roof for snow.
Installing or replacing mechanical equipment creates new penetrations. A check after this work reduces the risk that a poorly sealed connection goes unnoticed.
For a commercial building, the timing of the work matters as much as the type of work. A thorough assessment of the roof’s condition and the building’s needs makes it possible to know whether a repair, resurfacing or a roof replacement is needed, and to avoid unnecessary work.
Toitures OBM explains its recommendations clearly, so the owner or manager can plan the budget, choose the timing of the work and inform the occupants. For permits, check with your municipality.
Toitures OBM is located at 1215 Tellier Street in Laval and builds commercial flat roofs in Montreal, Laval and on the North Shore. The company works on commercial, industrial and multi-unit buildings: elastomeric roof replacement, new flat roof construction, repair, resurfacing, maintenance and inspection.
Toitures OBM is Soprema PAQ+S certified, CAA-Québec Recommended and holds RBQ licence 5778-2823-01. Financing is available through Financeit. The team can be reached Monday to Friday, from 8 a.m. to 5 p.m.
In many cases, yes. The installation method and the organization of the job site are chosen with the building’s activities in mind. The situation is assessed on a project-by-project basis.
Yes. Redoing the waterproofing around penetrations and equipment bases is part of flat roof repair.
Not necessarily. The assessment determines whether the problems are localized or whether the membrane is reaching the end of its life over the entire surface.
To have the flat roof of your commercial building assessed, contact Toitures OBM at 514-449-5469 or request a free quote using the form.
OBM Roofing
Elastomeric membrane specialists for commercial, industrial and multi-unit buildings in Laval, Montreal and the North Shore.
