On a Lower Mainland flat or low-slope roof, two-ply torch-on SBS costs about $9 to $16 per sq ft installed, TPO $8 to $14 and EPDM $7 to $13, before GST. Torch-on is the regional standard and the most robust; TPO is the lighter, reflective single-ply; EPDM is the budget rubber membrane. Here's how they differ, which suits which roof and what to ask for in a quote.
What's a flat roof here?
Anything under about a 2:12 pitch, where shingles aren't allowed: Vancouver Specials, post-and-beam houses, 1960s and 70s modernist homes, carports, garages, additions, and most commercial and strata buildings. The BC Building Code permits modified bitumen membranes from 1 in 50 up to 1 in 4 (about 2% to 25% slope); below 1 in 50 water ponds, and ponding is what kills flat roofs. See the flat roofing page for how a low-slope roof is built.
The three membranes compared
| Two-ply torch-on SBS | TPO | EPDM | |
|---|---|---|---|
| What it is | Two layers of SBS-modified bitumen, base sheet plus granulated cap sheet, heat-welded | Single-ply thermoplastic (polyolefin) sheet, seams hot-air welded | Single-ply synthetic rubber sheet, seams glued or taped |
| Installed, per sq ft | $9 to $16 | $8 to $14 | $7 to $13 |
| 1,500 sq ft roof | $15,000 to $24,000 | $12,000 to $21,000 | $9,000 to $15,000 |
| Expected life | About 20 years (general industry figure); well-maintained roofs go longer | 7 to 20 years in general references; newer formulations aim higher | 15 to 25 years |
| Thickness and toughness | Thickest, most puncture-resistant; tolerates foot traffic | Thin; punctures from dropped tools, mechanical equipment | Thin but flexible; punctures and shrinks with age |
| Seams | Heat-fused layers; very reliable when done well | Welded seams are strong when the welder is set right | Glued or taped; the weakest link, especially with age |
| Colour | Granulated cap, grey, white or coloured | White, reflective | Black (white available at a premium) |
| Fire during install | Open flame; needs a skilled, insured crew and a fire watch | No flame | No flame |
| Repairs | Easy: torch a patch | Welded patch, needs the right equipment | Glued patch, simple |
| Best for | Houses, complex roofs with many penetrations, decks over living space | Large simple roofs, commercial, where reflectivity matters | Budget jobs, garages, simple shapes |
Prices overlap Lower Mainland roofers' published 2025 and 2026 rates. Lifespans are general North American figures; no BC-specific study exists.
Torch-on SBS: the local default
Walk any Vancouver alley and most of the flat roofs are torch-on. Roofers here know it, suppliers stock it, and two plies of modified bitumen are hard to puncture and easy to flash around the dozens of vents, drains, skylights and parapets a flat house roof has. Granulated cap sheets come in light colours for reflectivity. The drawbacks: open-flame installation needs care (ask about the crew's torch-safety training and the company's insurance), it's heavy, and it's the most expensive of the three. For a house roof you'll walk on and want to last, it's the usual recommendation.
TPO: light, white and fast
TPO is a single welded sheet, white by default, and goes down quickly on big open roofs, which is why it dominates commercial work. The white surface reflects heat, useful over a top-floor bedroom. Its weaknesses are thinness (punctures from dropped tools or HVAC service), seam quality that depends entirely on the welder's settings, and a shorter track record than torch-on; early formulations had problems and general references give it a wide life range. On a small house roof with many penetrations, the labour of flashing each one in single-ply erodes the price advantage.
EPDM: the budget rubber
EPDM is a black synthetic rubber sheet, usually fully adhered or ballasted, with glued or taped seams. It's the cheapest, flexible in cold, and simple to patch. The seams are the weak point as adhesives age, and black EPDM gets hot. It's a sensible choice for a detached garage, a carport or a simple rectangular roof on a budget, and a compromise over living space you can't afford to have leak.
What makes a flat roof last, whichever membrane
- Drainage. Positive slope to drains or scuppers, drains kept clear, no ponding. Tapered insulation fixes a dead-flat deck.
- Flashing details. Parapets, curbs, pipes and drains are where flat roofs leak. Ask how each is detailed.
- Insulation and venting. Flat roofs framed with joists need 1-in-150 ventilation or an unvented design. Cold roofs over heated space need both done right.
- Protection from traffic. Walkway pads where anyone services equipment.
- Inspection. Twice a year: clear the drains, look at the seams and flashings.
Which should you choose?
House roof over living space, complex, long-term: torch-on SBS. Large, simple, commercial or strata roof: TPO or SBS, by quote. Garage, carport, tight budget: EPDM. Ask every roofer which membrane they install most; a crew that does torch-on every day will give you a better torch-on roof than a crew doing its third TPO job. Get the manufacturer's system warranty terms and the roofer's workmanship warranty in writing, and compare three quotes with the quote comparison guide. Our commercial roofing page covers strata and commercial flat roofs.
Common questions
Which flat roof lasts longest?
Well-drained two-ply torch-on SBS typically lasts 20 to 30 years here; TPO and EPDM ranges published by inspectors are wider and generally shorter. Drainage and flashing decide more than the membrane.
Is torch-on allowed on a house?
Yes, and it's the most common flat roof on Lower Mainland houses and additions. It involves an open flame, so it needs an experienced crew, a fire watch and care near wood siding and vents.