Blog
7 September 2026
A flat roof is practical and suits many buildings, but when it starts showing signs of fatigue, problems can pile up quickly. In Sainte-Agathe-des-Monts, as everywhere in Quebec, freeze-thaw cycles, snow buildup and spring rains constantly put stress on the membrane. A membrane that ages poorly eventually lets water through.
Before undertaking a complete flat roof replacement, it helps to understand what the project involves, when it becomes necessary and how it unfolds, step by step.
It is important to distinguish repair from roof replacement. A repair fixes a localized problem: a leak, a crack, a loose seam or a damaged section. A roof replacement instead involves removing all or a large part of the existing roofing system to start over on a sound base.
Several signs suggest a roof replacement should be considered: a membrane that blisters or cracks over large areas, significant separation around upstands and penetrations, leaks that keep coming back despite repairs, water that pools on the roof, moisture stains on ceilings or insulation that has lost its effectiveness.
An elastomeric membrane that is properly installed and regularly maintained can last several decades. Age alone is not enough to decide, however: a neglected roof may need replacing sooner than expected, while another one that has been carefully monitored can hold up for a long time. It is the actual condition of the membrane, the details and the insulation that guides the decision.
When the membrane is worn on the surface but the insulation is dry and the roof is still watertight, resurfacing may be an option: cleaning, preparing the existing membrane and applying a cap sheet. When water has reached the insulation or the membrane is deeply deteriorated, roof replacement is the preferred route.
A serious roof replacement follows a structured process, from the initial analysis to the installation of the final details.
First, the roof is inspected in detail: condition of the membrane, condition of the upstands and flashings, moisture in the insulation, water flow toward the roof drains and condition of the substrate. This analysis defines the actual scope of the work and avoids redoing what doesn’t need to be redone.
In most roof replacements, the old membrane is removed. Laying a new membrane over a deteriorated system may seem economical, but it hides the underlying problems. Wet insulation is also replaced, since waterlogged insulation loses its thermal value and promotes mould.
Once the old system is removed, the roof deck, that is, the wood or concrete base on which the roof rests, is inspected. Rotten or damaged sections are replaced before continuing. This is often the stage where surprises turn up on older buildings.
The new insulation is then installed, followed by the two-ply elastomeric SBS modified bitumen membrane: a base sheet and a cap sheet, torch-applied or self-adhered depending on the chosen system. Soprema systems, such as the mechanically fastened conventional or the self-adhered conventional system, are selected based on the substrate and the roof configuration.
The upstands and flashings are carefully redone around roof drains, vents and mechanical penetrations and along walls and parapets. Since many leaks start at these junctions, their execution deserves particular attention.
A few things help prepare the project. Check with your municipality whether a permit is required. Plan for roof access, space for materials and, in an occupied building, informing the occupants. Timing matters too: a roof replacement is ideally planned before leaks damage the insulation and the inside of the building.
The cost of a roof replacement depends on the area, the condition of the substrate, the insulation to be replaced, the chosen system and the complexity of the roof: number of penetrations, parapets, equipment. A detailed quote, prepared after the roof analysis, shows exactly what is included, such as insulation replacement or redoing the upstands. Interior water damage is often expensive to repair, and a roof replacement planned at the right time helps avoid it.
Toitures OBM specializes in elastomeric membrane flat roofs for commercial buildings, industrial and multi-unit buildings, as well as residential flat roofs. Based at 1215 rue Tellier in Laval, the company carries out flat roof replacement projects in Sainte-Agathe-des-Monts.
Before recommending a roof replacement, the Toitures OBM team assesses the condition of the roof and the needs of the building to avoid unnecessary work, then explains its recommendations clearly. The company is Soprema PAQ+S certified, CAA-Québec Recommended and holds RBQ licence 5778-2823-01. Financing is available through Financeit.
The duration depends on the roof area, the condition of the substrate, the amount of insulation to replace and the weather. A realistic timeline can be set once the roof has been analyzed and the scope of work is known.
Not necessarily. Wet or damaged insulation must be replaced, since it has lost its thermal value. Dry insulation in good condition can sometimes be kept. The roof analysis determines this.
Requirements vary from one municipality to another. Before the work, check with the Ville de Sainte-Agathe-des-Monts whether a permit is required for your building.
A well-planned and well-executed roof replacement protects your building for many years. To have your flat roof analyzed in Sainte-Agathe-des-Monts, contact the Toitures OBM team at 514-449-5469, Monday to Friday from 8 a.m. to 5 p.m., 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.
