Torch-Down Roofing Repair

“Torch-down” refers to a modified bitumen roofing system installed by heating the underside of the membrane with an open flame torch until it becomes tacky, then rolling it onto the roof surface where it fuses directly to the substrate. It’s a common system on both residential additions and commercial flat roofs.

Repairing torch-down roofing generally follows modified bitumen repair principles — flashing cement and fiberglass reinforcement for smaller patches — but larger repairs or full section replacement may require re-torching a new cap sheet, which demands proper safety precautions given the open flame involved. This isn’t a DIY-appropriate repair method for anyone without the right equipment and training.

One issue specific to torch-down roofs: improperly heated seams during original installation (either too little heat, which doesn’t fully fuse the layers, or too much, which can damage the material) create weak points that may not show up as a leak until years later. If a torch-down roof develops repeat leaks along seam lines with no other obvious cause, installation quality is worth investigating.