Torch-On vs Single-Ply Membrane for a Flat Roof in Victoria

Flat and low-slope roofs are more common in Greater Victoria than visitors expect. Gordon Head's 1960s and 70s split-levels and boxy two-storeys often have a low-slope wing that was re-covered in torch-on decades ago and is now due again. Fairfield and Rockland have mid-century post-and-beam homes with flat roofs by design, the Uplands has modernist houses, and almost every neighbourhood has a carport, sunroom or addition with a membrane roof draining to a single scupper. These are the region's biggest concentration of 'second re-roof' projects, and ponding after a December storm is the usual complaint.

The flame question is real in the older core. Torch-on is applied with an open-flame torch, which is why contractors get nervous beside cedar siding in Oak Bay, under a wood soffit in Fernwood or on a James Bay lot where the neighbour's wall is a metre away. Many keep a fire watch after the crew leaves; some switch to a self-adhered base sheet or a single-ply membrane for those details. Low-slope work also has its own WorkSafeBC rules: on slopes of 4/12 or less crews must stay 2 m from an unguarded edge without other protection, which shapes how a small townhouse roof is staged.

Two-ply SBS torch-on is modified bitumen: a base sheet is fastened or adhered to the deck, then a granulated cap sheet is heat-welded over it with a torch so the two layers fuse. The result is thick, tough and repairable with the same material. Single-ply means one sheet of TPO, PVC or EPDM, either mechanically fastened or fully adhered, with seams welded by hot air (TPO, PVC) or glued and taped (EPDM). No open flame is involved.

Neither is inherently better. Torch-on tolerates foot traffic and rough detailing better; single-ply is lighter, reflective in white and faster to lay on a big simple deck. On a small residential roof full of vents, a skylight curb and a parapet, the installer's familiarity with the system matters more than the system.

Torch-on is the regional default for good reasons.

• More local crews do it every week, so quotes are easier to get and compare
• It is robust at seams, corners and penetrations, the places flat roofs leak
• Patches and future tie-ins (an addition, a new skylight) use the same material
• Inspectors and buyers know what they are looking at
• Published BC pricing is consistent: Taves $8–$12, Citadel $10–$13+ per sq ft, with 25–30 year lifespans quoted

Choose membrane when one of these applies, and choose the crew as carefully as the product.

• Open flame is a genuine risk: cedar or wood siding, a wood soffit, a shared wall on a tight lot
• The deck or structure needs a lighter system
• A reflective white surface is wanted over a sunroom or bedroom that overheats in the dry summer
• The roof is large and simple, where welded single-ply seams go down fast
• The contractor installs the chosen membrane regularly and offers a manufacturer-backed warranty on it

Flat roofs fail at water that does not leave. Positive drainage to a scupper or drain, tapered insulation where a deck has settled, clear drains before every December, and parapet and wall flashings that turn up high enough are what separate a 15-year flat roof from a 30-year one. Ponding shortens the life of torch-on and membrane alike.

Guarantees are the other lever. RCABC's RoofStar program offers 5, 10 and 15-year third-party guarantees on systems installed by member contractors with independent inspections; it is worth asking whether your job qualifies, especially on a larger flat roof where the seam and drainage detailing is hard for an owner to judge.