How long does a torch-on roof last and how is it maintained in BC?

Gordon Head is the torch-on capital of the region: 1960s and 70s ranchers, split-levels and boxy two-storeys with low-slope sections that were re-covered in torch-on when the original tar-and-gravel failed. Many of those torch-on roofs are now 20 to 25 years old, which makes it the biggest concentration of second-generation flat-roof replacements in Greater Victoria, and the age of the torch-on section is often different from the shingled part of the same house.

Elsewhere the question comes up on mid-century Fairfield and Fernwood additions, carports and sunrooms across Saanich and Esquimalt, and on West Coast modern homes in North Saanich and Metchosin with large, nearly flat roofs under trees. Needle drop is the enemy on those: it blocks scuppers and drains, water ponds, and the ponded corner is where the membrane ages first.

Torch-on is a two-layer modified bitumen system: a base sheet and a granulated cap sheet, heat-welded to each other and to the substrate. The bitumen ages under UV and thermal cycling, which is slow on a roof that drains and fast on one that ponds, because standing water keeps the cap cool on one side and hot on the other and finds every pinhole. Seams and flashings age fastest because they are where the membrane bends.

Installation quality is the other half. A crew that welds every lap fully, primes the metal, runs the membrane up walls and curbs to the right height and sets drains flush is what the RCABC guarantee program inspects for on flat roofs, and why a guarantee is often worth more on torch-on than on shingles.

Flat roofs are the one place where a small annual habit changes the lifespan.

• Clear drains, scuppers and gutters in late fall and again in spring
• Keep trees trimmed back so needles and branches stay off the membrane
• Have seams, flashings and sealant checked yearly; small re-welds and sealant renewals are cheap
• Address ponding with a tapered insulation or drain fix rather than waiting
• Limit foot traffic; if HVAC or antennas need service, use walkway pads
• Consider a reflective coating in the last third of the roof's life to slow UV aging, if the cap is sound

Torch-on is repairable: a split seam or a failed flashing is a $400–$1,500 flashing-type repair in our model, and localised patches are routine. Coating a sound but aging cap sheet can buy several years. Replacement is the answer when blisters and cracks are widespread, the deck is soft underfoot (a sign of trapped water), or the roof is at 25+ years with recurring leaks. At that point the choice is torch-on again or a single-ply membrane, which the torch-on-versus-membrane page compares; both sit at $9–$16 per sq ft of roof in our model, with the deck condition driving the final number.