Modified Bitumen

Modified Bitumen Roofing in San Francisco

Modified bitumen is a proven flat roofing system that has been protecting Bay Area buildings for decades. The multi-layer, torch-applied membrane creates a robust, flexible waterproofing system that handles the thermal expansion, contraction, and moisture conditions common on San Francisco flat roofs.

Ascender Roofing Solutions installs modified bitumen roofing for both residential flat sections (additions, garages, porches) and commercial flat roofs. Our crews are trained in proper torch-down application techniques that ensure complete adhesion and seam integrity.

Get a free estimate (415) 728-2724

Quick specs

Expected lifespan20 to 30 years
Typical SF replacement$8,000 to $30,000
Best for
Flat roofsMulti-layer protectionResidential additions

Key benefits

Multi-layer system provides redundant waterproofing protection
Excellent flexibility handles thermal movement without cracking
Proven track record (decades of reliable performance in Bay Area conditions)
Self-healing properties (minor punctures can seal in warm weather)
Good foot traffic resistance for maintenance access
Compatible with granulated cap sheets for UV protection
Can be installed over existing flat roof systems in some cases

Things to consider

Torch application requires experienced, safety-trained installers
Darker surface absorbs more heat (may not meet cool roof requirements without a reflective coating)
Heavier than single-ply membrane systems
Seam quality depends on installer skill (proper torch technique is critical)

Torch-down roofing

Torch-down is the most common way modified bitumen is installed. Layers of membrane are heat-welded to each other and to the base, so the seams fuse together instead of relying on adhesive. It takes trained crews and fire-safety procedures on site, which is how we run every torch-down job.

How many layers your roof gets

Most modified bitumen systems use a base sheet and a granulated cap sheet. Some roofs get an extra ply for added protection, often called a three-ply system. We specify the layers for your roof in the written proposal.

Replacing old tar and gravel roofs

Many San Francisco buildings still have tar and gravel (built-up) roofs. When they fail, we tear them off down to the deck, repair the decking where needed, and replace them with a modified bitumen system. Flat roofing →

Cool roof options

Dark cap sheets absorb heat. Reflective cap sheets and coatings are available, and California's energy code can require cool roof materials on some roof replacements. We confirm what applies to your building in the proposal.

Cost

Modified bitumen roof replacements in San Francisco typically run $8,000 to $30,000 depending on size, access, decking condition, drainage and the number of layers.

See how roofing is priced in San Francisco in the Roofing Cost Guide →

Questions about modified bitumen

What is torch-down roofing?+
A way of installing modified bitumen in which the membrane layers are heat-welded together, so the seams fuse rather than relying on adhesive.
How long does a modified bitumen roof last?+
Typically 20 to 30 years with regular maintenance, such as keeping drains clear and inspecting seams and flashing.
How much does modified bitumen roofing cost in San Francisco?+
Typically $8,000 to $30,000, depending on roof size, access, decking condition, drainage and the number of layers. Your written proposal gives the exact price.
Can modified bitumen go over an existing roof?+
Sometimes, if the existing roof is sound and code allows another layer. Often a tear-off is the better choice. An inspection decides.
Is torch-down roofing safe on a house?+
Yes, when it is done by trained crews following fire-safety procedures, which is how we run every torch-down job.
Do you replace tar and gravel roofs?+
Yes. We remove the old built-up roof, repair the decking where needed, and install a modified bitumen system.

Other roof types we install

Shingle RoofingFlat Roofing

Get a free modified bitumen estimate

Call or request a free estimate online. We respond within one business day.

Request free estimate (415) 728-2724