What is the difference between torch-on, TPO, PVC and EPDM?

In Greater Victoria the honest starting point is that torch-on is what the flat-roof crews do. Gordon Head's low-slope ranchers, Fairfield's mid-century additions and the carports and sunrooms across Saanich have been re-covered in torch-on for thirty years, so it is easy to get three comparable quotes. Single-ply residential installers exist but are fewer, which affects both price and how long you wait.

Where single-ply earns a look locally is where a flame is unwelcome: a James Bay or Fernwood cottage with cedar siding and a neighbour's wall a metre away, a roof deck over living space with old dry framing, or a strata in Langford whose insurer has opinions about torches. White TPO or PVC also suits the big, sun-exposed flat roofs of West Coast modern homes in North Saanich, where summer heat gain through a black roof is noticeable.

Every flat roof has to do the same thing: keep a continuous waterproof layer over a deck that barely slopes, with every seam, drain, vent and wall joint sealed. The families differ in how the seams are made. Torch-on fuses bitumen to bitumen with heat, giving a thick, forgiving lap; thermoplastics (TPO, PVC) weld with hot air into a single sheet; EPDM relies on adhesive and seam tape, which is why its seams get the most attention at inspection.

Thickness and weight follow from that: torch-on is the heaviest and most puncture-tolerant, single-ply the lightest and most vulnerable to a dropped tool or a dragged ladder.

A few practical tests sort most homes.

• Is there cedar siding, a close neighbour or old dry framing nearby? Lean single-ply to avoid flame
• Is the roof large and sun-exposed with living space below? White TPO or PVC cuts summer heat
• Are there many penetrations, curbs and walls? Torch-on's thick laps are forgiving at details
• Will foot traffic (HVAC, decks, solar) be regular? Torch-on or PVC with walkway pads over EPDM
• How many local crews can quote it? Torch-on gives the most comparable quotes; ask single-ply installers for local references
• Is a third-party guarantee wanted? RCABC's program covers both families through member contractors

In our pricing model torch-on and single-ply both run $9 to $16 per sq ft of roof; BC guides put torch-on at $8 to $13+ and a Canada guide puts membranes at $11 to $22. Lifespans overlap at 20 to 30 years for all four. What fails is rarely the sheet: it is ponding water, blocked drains, flashings at walls and vents, and seams that were not welded or taped properly on day one. Whichever system you pick, spend the money on drainage and detailing and get the scope in writing.