Flat roof and elastomeric membrane in Montreal, Laval and the South Shore
Duplex, triplex or roof terrace: a flat roof calls for different expertise than a pitched one. We install and replace durable elastomeric membrane systems, with particular attention to drainage and watertight detailing at the upstands.
- ✔Two-ply membrane system
- ✔Rigid insulation and vapour barrier
- ✔Sealed drains and upstands
- ✔10-year workmanship warranty
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RBQ
Licensed & insured
Régie du bâtiment compliant
2M$
Liability coverage
Full job-site protection
10 years
Workmanship warranty
On our installations
★★★★★
Satisfied clients
Verified reviews
6+ ans
Of experience
Since 2020
300+
Roofs completed
In Montreal and nearby
Flat roof
The flat roof is a fact of life in Montreal
A large share of Montreal's housing stock — the duplexes, triplexes and small apartment buildings of the Plateau, Rosemont and Villeray — is covered with a flat elastomeric membrane roof rather than a pitched one. The system gives you usable roof space and suits the tight architecture of urban rows, but it demands rigorous execution: unlike a pitched roof, water does not run off on its own and depends on well-planned drainage.
At Toiture AM we install and replace elastomeric membrane systems while respecting the minimum slopes required, the placement of the drains and the watertightness of every upstand — the points where the large majority of flat-roof leaks begin.
Signs a flat roof needs inspecting or replacing
Persistent ponding water
Water still sitting 48 hours after rain points to a slope or drain problem.
Blisters and bubbling
Moisture trapped under the membrane forms bubbles that worsen over time.
Cracks at the upstands
Junctions with parapets and walls are the first failure points to watch.
Over 20 years old
A well-installed elastomeric membrane generally has a 20 to 25-year service life.
Our elastomeric membrane system
A two-ply system built for lasting watertightness.
Base membrane
First ply, mechanically fastened or fully adhered, forming the watertight foundation of the system.
- ✓Torch or self-adhesive compatible
- ✓Puncture resistant
Cap membrane
Granulated top ply, continuously exposed to weather and UV.
- ✓Reflective granules available
- ✓Manufacturer warranty up to 20–25 years
Rigid insulation
Insulation boards installed under the membrane to improve the building's energy performance.
- ✓Reduces heating costs
- ✓Can create slope where the deck has gone perfectly flat
Soprema
Quebec manufacturer, the benchmark for elastomeric membranes in this climate.
- ✓High-performance SBS lines
- ✓Widely used on Montreal plexes
Our flat roof process
Inspection and moisture test
Assessing the existing membrane and insulation to find trapped moisture.
Detailed quote
Written estimate specifying the membrane system, the insulation and a guaranteed fixed price.
Removal and preparation
Stripping the old membrane where necessary and checking the deck.
Insulation and slope
Rigid insulation laid, correcting the slope toward the drains where required.
Base and cap membrane
The two-ply system installed with careful detailing at every upstand.
Sealing drains and parapets
Sealing the critical points where most leaks originate.
Final inspection
Checking how water runs off, and handover of your warranty documents.
Understanding your flat roof
"Flat" does not mean without slope
A well-designed flat roof always keeps a minimum slope — usually around 2% — toward the drains. Without it, water sits after every rainfall, accelerates the membrane's deterioration and eventually works in at the weak points. On many Montreal plexes built decades ago, that original slope has often sagged over time.
Drains, the most neglected detail
A drain blocked with debris or poorly sealed to the membrane is the single most common cause of leaks on a flat roof. Simple annual maintenance — clearing the drains before autumn — prevents a large share of the problems we see on roofs over 15 years old.
Torch or self-adhesive: which method to choose
Torch application gives very reliable adhesion but requires a hot-work permit and strict precautions. Flame-free self-adhesive membrane suits renovations in dense urban settings where fire safety is a priority, particularly on semi-detached buildings.
Insulation, often the missed opportunity
Replacing a flat roof without improving the insulation under the membrane is a missed opportunity: rigid insulation boards cut heat loss in winter and, where needed, let us rebuild an adequate slope on a deck that has gone perfectly flat over the years.
Reflective white membrane: an option worth considering
A cap membrane with white granules reflects more solar radiation than a traditional dark membrane, which reduces the heat stored in summer. It is a worthwhile option to discuss with us depending on how your roof is laid out.
Indicative price for an elastomeric membrane flat roof
Cost varies with surface area, the condition of the existing insulation and how accessible the roof is. An apartment building with several drains and upstands generally costs more per square foot than a small, simple surface.
$8,000 – $20,000
For a typical duplex or triplex flat roof in Greater Montreal. Firm pricing follows an on-site inspection.
Flat Roof & Elastomeric Membrane — Areas we serve
We work across the island of Montreal, in Laval and throughout the South Shore.
Frequently asked questions — Flat Roof & Elastomeric Membrane
Clear answers to the questions we get asked most about this service.
How long does an elastomeric membrane last?
A well-installed two-ply elastomeric membrane system generally lasts 20 to 25 years, depending on how well it is maintained and how well the roof drains.
Why does my flat roof have standing water?
Water still standing after 48 hours usually indicates insufficient slope toward the drains or a blocked drain. A deck that has sagged over time can also be the cause — an inspection confirms exactly which.
Does the old membrane have to come off before a new one goes on?
That depends on the condition of the existing system and whether moisture is trapped underneath. In many cases a new membrane can go over top if the deck is dry and sound; otherwise full removal is recommended.
How much does a flat roof replacement cost?
Expect roughly $8,000 to $20,000 for a typical duplex or triplex, depending on area and the condition of the existing insulation. Firm pricing always requires a site visit.
Is a flat roof more prone to leaks than a pitched roof?
A well-designed flat roof with adequate slope and clear drains is not inherently more at risk. Risk rises mainly with the age of the system, neglected maintenance, or insufficient slope from the outset.
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Ready to start your flat roof project?
Get in touch for a free inspection and a detailed quote built around your actual roof.