EPDM vs Torch-On: Flat Roof Options in Saskatoon

Shingles only work because the slope carries water down over each overlap before it can find a gap, so on a flat section, where water just sits, they leak. That section needs a continuous membrane sealed against the water.

Plenty of Saskatoon houses have a bit of this somewhere, like a garage roof, a back addition, a low porch or a flat stretch between two gables, and it needs a different system from the shingles on the rest of the house.

EPDM is a synthetic rubber membrane, the thing most people mean when they say rubber roof. It goes down in large sheets, so a small roof may only have a few seams, and it stays flexible in the cold. A roof here goes from summer heat to forty below, and a membrane that moves with that without cracking suits the climate.

No open flame goes into the install, which some owners prefer on a section tied into the wall of the house. A puncture or a lifted seam can be patched later with the same material.

Where it gets into trouble is the seams and the details, the spots where two sheets meet or the membrane turns up a wall or wraps a vent. That is where water tries first, and rushed seam work shows up there as leaks.

Torch-on, also called modified bitumen, is built in layers. The installer heats the underside of each roll with a torch as it unrolls, melting the bitumen so it fuses to the layer underneath, and the top usually carries a granulated finish.

The appeal is toughness. It takes foot traffic better than a single sheet of rubber and there is another layer behind the top one if it gets damaged, which counts on a flat roof somebody walks across to reach equipment.

The catch is the open flame. It has to go on with a crew that does torch-on regularly and knows how to work a torch safely near the wood and flashing where a flat roof meets the house.

Almost always at the seams, the flashing and the drainage. The middle of the membrane rarely wears through on its own. Water gets in at a joint, at the edge where the roof meets a wall, around a vent or drain, or at a low spot where it has been sitting for weeks.

Ponding is the one to watch. A flat roof still needs enough fall to move water to a drain or an edge, and a low spot that holds water after every rain will eventually find the weakest seam near it. In winter that puddle freezes, thaws and freezes again right on top of the membrane and the flashing around it. When we replace an old flat roof the drainage gets as much attention as the membrane, since a new membrane over the same low spot tends to fail in the same spot.

Hail is the other prairie problem. A bruise or puncture in the membrane lets water sit and work its way in, so after a storm check the flat part of the house even if the shingled part looks fine. Our guide on what to do after a hail storm covers what to look for.

How the roof gets used matters most. If people will be up there servicing equipment or clearing snow, torch-on's tougher surface earns its keep, while a garage roof nobody touches from one year to the next is a natural fit for EPDM.

Look at what the flat section connects to as well. A lot of flat sections butt right against a sloped roof, and that joint is where the detailing counts. If the sloped part needs work at the same time we quote it as roof replacement or metal, and the water coming off the flat section is eavestrough work. Budget comes into it too, and at the inspection we walk you through which system fits.

If the old flat roof failed, find out why before picking the new one. A roof that leaked because water pooled against a wall will leak again with either membrane unless the drainage gets fixed.