Torch-on, TPO and EPDM are the three main membranes for flat roofs in Calgary, and all three can keep water out for years when installed well. For most Calgary homes and garages, we recommend two-ply torch-on. We use TPO or EPDM where one of them suits a particular roof better.
Here’s how they differ, and what decides which one fits your roof.
What’s the difference between torch-on, TPO and EPDM?
Torch-on, also called SBS modified bitumen, is asphalt reinforced with rubbery polymers. It goes down in two layers: a base sheet, then a cap sheet with granules on top, heat-fused together. IKO, whose membranes we use, makes its torch-on rolls about one metre wide.
TPO is a single layer of smooth plastic membrane, usually white, with its seams welded by hot air. EPDM is a single layer of black synthetic rubber in wide sheets, with seams joined by tape or adhesive.
You can usually tell which one you have by touch. Torch-on feels gritty like a shingle. TPO is smooth and often white. EPDM is black and feels like an inner tube.
How does each one handle Calgary cold, chinooks and hail?
All three are used across Canada, but they behave differently in our weather.
| Torch-on (2-ply SBS) | TPO | EPDM | |
|---|---|---|---|
| Layers | Two, fused together | One | One |
| Seams | Heat-fused, offset between plies | Hot-air welded | Taped or glued |
| Top surface | Granules, takes foot traffic well | Smooth, reflects sun | Smooth rubber |
| Hail and punctures | Two plies to get through | One layer | One layer |
| Open flame on site | Yes, unless flameless sheets are used | No | No |
Calgary’s chinooks swing a roof from frozen to thawing and back. The City of Calgary counts an average of 128 freeze-thaw cycles a year. That movement is hardest on seams and flashings, which is where most flat roof leaks start.
Does torch-on really have more seams, and does that mean more leaks?
It has more seams, but they behave differently. Torch-on comes in narrow rolls, so a garage roof has more laps than the same roof in a wide EPDM sheet. That’s the most common objection people raise online.
The two plies are offset, so a lap in the cap sheet sits over solid base sheet, not over another lap. Water has no straight path through. On single-ply TPO and EPDM, each seam is the only layer, so the quality of that one weld or tape joint carries more weight.
Is torch-on safe on a house or garage with a wood deck?
It is when the crew follows the industry’s fire guidance. The Canadian Roofing Contractors Association says most rooftop torch fires start at flashings, roof edges and penetrations, where flame can reach wood or debris hidden behind them.
Its guideline is no open flame directly on a wood deck, and flameless self-adhered or heat-free sheets around those risky details, running well into the roof. Ask any torch-on contractor three things: how the base sheet goes on over wood, which details are done flame-free, and whether someone stays on fire watch after the torches go off.
What happens when water ponds on a flat roof?
Some water after rain is normal. Water that sits for days isn’t. A common rule of thumb in the trade is that it should drain or evaporate within about 48 hours of a rain.
Ponding is one of the signs we look for when deciding between a repair and a replacement, along with blisters, cracks, open laps and worn granules. In Calgary there’s a twist: a pond that hasn’t drained by nightfall can freeze, and ice expanding at a lap works it open. Check for ponding during a warm spell, not the day after a cold snap.
The fix for ponding is usually slope, not a different membrane. Tapered insulation under the new roof can steer water to the drain. If ponding is excluded in a quote’s fine print, ask why.
Which flat roof fits a garage, a rooftop deck or a condo building?
Garages and additions are where most homeowners meet flat roofs. Two-ply torch-on suits them well, because its granule surface stands up to the odd foot on the roof better than a smooth single ply.
Rooftop decks need a membrane that can sit under a deck system and stay accessible for repairs. Condo and commercial buildings bring bigger roofs, rooftop units and drains, which is why we choose the system per building. Our commercial roofing page covers larger roofs.
What does a flat roof cost in Calgary?
It depends on the size, the insulation underneath, how many drains and penetrations there are, and how much old roof comes off. Our commercial flat roof replacements typically run $10 to $20 per square foot.
Smaller jobs cost far less. A typical flat roof leak repair from us runs $350 to $2,500. If you’re not sure whether yours needs a repair or a full replacement, our flat roof repair page walks through the signs.
Common questions
Is TPO better than torch-on?
Not overall. TPO is a good single-ply membrane with welded seams and a reflective surface, and it suits some roofs better. For most Calgary homes and garages, two-ply torch-on gives a tougher surface and two layers of protection.
Can you walk on a flat roof?
Torch-on’s granule surface handles light foot traffic best. TPO and EPDM can be walked on carefully, but sharp objects and heavy traffic can damage a single-ply membrane, so walkway pads help where people go often.
Can a flat roof be installed in winter in Calgary?
Often, yes, on dry days. Torch-on is heat-applied, so cold is less of a barrier than snow, ice and wind. The Canadian Roofing Contractors Association notes some self-adhered sheets can go down at temperatures as low as minus 10°C. Glued and taped seams on single-ply roofs are fussier in the cold, so ask how your roofer handles a winter job.
How long does a torch-on roof last?
It depends on the install, the slope and how well water drains, so we don’t quote a lifespan we can’t stand behind. Our flat and commercial roofs carry a 10-year workmanship warranty.
See how we install flat roofs on our flat roofing page, or call 403-608-9933 to have yours looked at.
