How to Repair a Torch Down Roof: Best Options Explained

Torch down roofing (modified bitumen) is common on commercial and low-slope residential buildings. When it develops leaks or shows age, here are your best repair options.

Understanding Torch Down Failure Modes

Modified bitumen roofs most commonly fail at: laps and seams where torch welding has separated or never fully bonded, granule loss exposing the bitumen to UV degradation, blistering from trapped moisture below the membrane, and flashing failures at penetrations and transitions.

Option 1: Torch Repair of Failed Seams

For isolated seam failures on otherwise sound systems, a qualified roofer can re-torch failed laps and re-seal problem areas. This is the lowest-cost short-term repair but doesn't address overall membrane aging.

Option 2: Silicone Coating Over Modified Bitumen

A silicone coating system can be applied directly over granulated modified bitumen roofing. The coating fills in granule gaps, seals all laps and transitions, and creates a new continuous waterproof surface with a 10–20-year renewable warranty. This is the most cost-effective long-term option for granulated mod-bit roofs in acceptable condition.

Option 3: Spray Foam Restoration

For smooth modified bitumen roofs or those with significant blistering, spray foam applied over the existing membrane provides superior adhesion and creates a completely seamless new surface. Foam also adds insulation value and corrects any drainage issues.

Option 4: Full Replacement

Required when the membrane has extensive delamination or wet insulation exceeds 25% of the roof area.