Flat roofing · Metro Vancouver & the Fraser Valley
What is torch-on roofing, and why is it on so many Lower Mainland roofs?
Torch-on roofing is a flat-roof system made from SBS modified bitumen sheets that are bonded to the roof with a propane torch. The flame melts the underside of the sheet so it fuses to the surface below, forming one continuous waterproof membrane with nothing fastened through it. It is installed in two plies (a base sheet and a cap sheet) and on a well-drained roof it lasts twenty to thirty years.
It is the default flat-roof system between West Vancouver and Chilliwack for one reason: it copes with standing water and months of rain better than anything else at the price.
- 5-year workmanship warranty on torch-on, in writing
- 500+ roofing jobs
- WorkSafeBC registered
- $5M liability insured
- GAF certified
- Brava Preferred Contractor
- ICBA & BBB member
How it is built
Two plies, bonded, with nothing through the membrane.
A two-ply SBS torch-on roof is put down in layers, each one doing a different job. On our installations that means an IKO TP-180 base sheet and a TP-250 granulated cap sheet.
- The deck is inspected and repaired first. Plywood that has gone soft under an old membrane is replaced before anything is bonded to it, because a membrane is only as flat and as sound as what is under it.
- The base sheet goes down over the prepared deck and is bonded across its full surface. This is the ply that does the waterproofing; nothing is screwed through it.
- The cap sheet is torched over the base with staggered laps, so no seam in one ply sits over a seam in the other. Its mineral granules take the ultraviolet load and the foot traffic.
- Details last: drains, scuppers, parapet walls, curbs and any penetration get their own flashing plies, lapped into the field. This is where flat roofs are won and lost, and it is where the hours go.
The result is a membrane with no mechanical fasteners through it and no seam that relies on adhesive alone. Water that sits on it has nowhere to go but off the edge.
Why here
What our rain does to a flat roof.
How much rain a building takes depends entirely on where it stands. Environment and Climate Change Canada's Canadian Climate Normals record 1,189 mm of precipitation a year at the Vancouver International Airport station on the 1981 to 2010 normals, 1,538 mm at the Sardis station in Chilliwack and 2,155 mm at the Pitt Polder station in Pitt Meadows, both of those on the 1981 to 2007 normals. What does not change anywhere on that range is the timing: most of it falls between October and March. A flat roof here is not being asked to shed a summer storm and dry out. It is being asked to sit under water, on and off, for five months.
That rules out a lot of systems that work perfectly well elsewhere. Anything that depends on hundreds of fasteners, or on seams sealed with adhesive, is being tested continuously for half the year. A fully bonded two-ply membrane is not.
The second local factor is that very few "flat" roofs are flat. Additions, garages, suites and mid-century houses across the Lower Mainland have roofs with a slope of a quarter-inch to the foot or less, and after twenty years of settling, some of them have low spots that hold water for days.
Torch-on handles ponding better than the alternatives, but nothing handles it indefinitely. Where a roof ponds badly enough to matter, correcting the slope with tapered insulation is a separate conversation and a separate line on the quote, not something to bury inside a membrane price.
Where it goes
The roofs that get torch-on.
Torch-on is not only for commercial buildings. On residential work in this region it turns up in four places over and over.
- Garages and carports: often the first flat roof on a house to fail, because nobody looks at it.
- Additions and rear extensions: the low-slope roof over a kitchen addition or a laneway suite, usually tied into a sloped roof at a wall, which is exactly where the detailing has to be right.
- Sun decks and roof decks: a membrane under a walking surface, where the waterproofing has to outlive whatever is sitting on top of it.
- Mid-century and modern homes: whole houses with low-slope roofs, common on the North Shore and in parts of Vancouver and Burnaby.
On mixed roofs (a sloped shingle roof with a flat section behind it) the transition between the two systems is the detail that matters most, and it should be flashed as one job by one crew rather than split between trades.
The honest comparison
Torch-on against the alternatives.
What torch-on does better
- Copes with standing water, which is the local failure mode
- No fasteners through the waterproofing layer
- Takes foot traffic and rooftop equipment without puncturing easily
- Repairs cleanly: a patch is bonded in the same way as the original
- Two plies mean a single defect is rarely a leak
What it asks of you
- A dry deck, so installation waits on the weather
- Open flame on a roof, so the crew and the setup matter
- Drains kept clear: the one piece of maintenance that decides its lifespan
- A five-year workmanship warranty rather than the ten years carried on shingle, metal and cedar work
We install two-ply SBS torch-on for flat roofs. We do not install TPO. If you have been quoted TPO elsewhere and want to understand the difference before deciding, the answer is in the questions below.
Lifespan
Twenty to thirty years, decided by the drains.
Two torch-on roofs installed in the same week by the same crew can be ten years apart in service life, and the difference is almost always water leaving the roof.
A roof where the drains and scuppers stay clear, where debris is swept out of the low spots, and where the flashings at walls and curbs get a look every couple of years will run to the top of that range. A roof where a drain has been blocked by fir needles since 2019 will not.
This is why most flat-roof failures we are called to are not failures of the membrane at all. They are a blocked drain, a cracked seal at a vent curb, or a wall flashing that was never lapped high enough. All three are cheap to fix and expensive to ignore.
Questions
Torch-on, plainly answered.
What is torch-on roofing?
Torch-on roofing is a flat-roof system made from SBS modified bitumen sheets that are rolled out and bonded to the roof with a propane torch. The heat melts the underside of the sheet so it fuses to the surface below, creating a continuous waterproof membrane with no mechanical fasteners through it. It is normally installed in two plies: a base sheet and a cap sheet.
What does SBS stand for in roofing?
Styrene-butadiene-styrene, a rubber compound blended into the asphalt. It is what lets the membrane stay flexible in cold weather and move with the building instead of cracking. SBS is the reason torch-on suits a climate that swings between wet and freezing.
Why is torch-on the standard for flat roofs in the Lower Mainland?
Because our flat roofs are rarely perfectly flat and it rains for months at a time. A fully bonded two-ply membrane has no fasteners through it and no field seams that rely on adhesive alone, so standing water sits on it without finding a way in. It also takes foot traffic better than single-ply systems, which matters on roofs with HVAC equipment.
How long does a torch-on roof last?
Twenty to thirty years is the normal service life for a well-detailed two-ply system in this climate. Drainage does more to decide that than anything else: a roof where water leaves quickly lasts at the top of that range, and a roof that ponds after every storm lasts at the bottom.
What is the difference between torch-on and TPO?
Torch-on is asphalt-based and heat-welded in two plies. TPO is a single-ply plastic membrane that is usually mechanically fastened and hot-air welded at the seams. We install two-ply SBS torch-on and do not install TPO.
Can torch-on be installed in the rain?
No. The deck and the surface being bonded to have to be dry, so torch-on work waits for a dry window. In the Lower Mainland that usually means work is scheduled around the forecast rather than the calendar, and emergency leak work is handled as a temporary repair until the weather allows a proper installation.
Does a torch-on roof need maintenance?
Yes, and it is the cheapest maintenance in roofing. Keep the drains and scuppers clear, clear debris from low spots, and have the flashings and seams looked at every couple of years. Most torch-on failures start at a blocked drain or a detail at a wall, not in the open field of the roof.
What warranty comes with a torch-on roof?
Five years on the workmanship of a torch-on or flat membrane installation, which is the standard for flat systems and shorter than the ten years carried on shingle, metal and cedar work. The membrane manufacturer's own warranty runs separately and longer.
Next
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