Torch-on vs TPO vs PVC vs EPDM: which flat roof for Kootenay winters

Four membranes cover most of the flat roofs in the West Kootenays: torch-on, TPO, PVC and EPDM. All four can give you a dry building. The differences show up in how they go on, how they handle our winters, and how they get repaired ten years in.

We install torch-on, TPO and PVC. We do not install EPDM, but it is a legitimate system that plenty of good roofers sell, so it gets the same fair treatment here as the ones we carry.

Here is what each one is, where it shines, and the honest trade-off that rarely makes the brochure.

Torch-on (SBS modified bitumen)

Torch-on is asphalt sheet, reinforced and modified with rubber, applied in two plies with an open-flame torch that melts the layers into one another. It is the workhorse membrane on commercial and industrial decks around Trail.

Where it shines: toughness. Two plies means a backup layer under the surface you can see, and the finished roof takes foot traffic, dropped tools and shovelled snow without complaint. Repairs are straightforward: heat a patch, weld it in.

The honest trade-off: it involves an open flame on your building. The crew’s skill and fire-watch discipline matter as much as the material, and it is the heaviest system of the four, so the structure has to carry it.

TPO (thermoplastic polyolefin)

TPO is a white thermoplastic sheet laid in one ply, with seams joined by hot-air welding: no glue, no flame. It went from newcomer to the most common flat membrane in North America in about two decades.

Where it shines: welded seams become one continuous piece of material, the white surface reflects summer heat, and installs move fast on big open decks like warehouses and shops.

The honest trade-off: it is one ply. There is one layer between the weather and your deck, so the detailing has to be right the first time. Formulations also vary between manufacturers more than the shared name suggests.

PVC

PVC is the other welded one-ply sheet, a thermoplastic kept flexible by plasticizers, with the longest history of the weldable membranes.

Where it shines: chemical and grease resistance. Restaurant exhaust and shop fumes that soften other membranes mostly bounce off PVC. It also stays weldable for years, so an aging PVC roof can usually be repaired rather than replaced.

The honest trade-off: the chemicals that keep it flexible slowly work their way out, and the sheet stiffens with age. It also doesn’t sit directly against asphalt products, so details near existing torch-on need separation layers.

EPDM

EPDM is black synthetic rubber, the oldest of the one-ply membranes, with a long record in snow country. Seams are glued or taped rather than welded.

Where it shines: the rubber stays flexible in deep cold, the install is simple, and the track record is real. Plenty of Kootenay buildings wear EPDM and wear it well.

The honest trade-off: the seams rely on adhesive and tape instead of a weld, and seams are where flat roofs fail. The black sheet also runs hot in summer.

To be plain about our own position: we install torch-on, TPO and PVC, and we don’t install EPDM. Not because it fails, but because our crews torch and weld every week, and you want your installer doing what they do daily. If EPDM is what your building wants, say so when you call and we’ll tell you straight.

Which one for your building?

There are no prices and no lifespan figures in that table on purpose. What your building needs depends on the deck, the drainage and what the roof has to put up with. That is what a site visit is for.