TPO or torch-down: what does a new flat roof cost in San Francisco?

What's the difference between TPO and torch-down?

There are two families on most Bay Area flat roofs. Single-ply membranes (TPO, PVC, EPDM) go down in large sheets with welded or glued seams. Asphalt-based systems (torch-applied or self-adhered modified bitumen, built-up roofing) go down in layers. Spray foam with a protective coating is a third route, common on some mid-century homes.

How long does each flat roof system last?

Service life differs by system. InterNACHI's chart (source):

What drives the price of a flat roof replacement?

• Drainage: new drains, scuppers or tapered insulation to stop ponding
• Parapets: wall flashing and caps
• Insulation: rigid board above the deck changes roof height and edge details
• Tear-off: old layers and wet insulation must come out
• Access: hoisting rolls and debris on tight lots

Does my flat roof need to be a cool roof?

San Francisco is in climate zone 3. The 2025 Energy Code's prescriptive cool-roof rule for low-slope reroofs applies in zones 4 and 6 through 15, so it doesn't apply to a city home reroof. See the CEC compliance manual.

What's different about flat roofs in San Francisco?

San Francisco has more flat roofs than any other Bay Area market we cover. Rows of Sunset, Richmond and Excelsior houses have nearly flat roofs behind a parapet, and many Victorians hide a flat rear section behind a pitched front. That shapes the job: the parapet walls need new flashing and cap, the drains or scuppers need to keep up with winter storms, and debris often has to come down through the house or by hoist. Torch-applied membranes have long been common on city roofs; with homes touching on both sides, ask how the crew manages fire safety and what they use where a torch isn't appropriate.

How do I choose a system and a roofer?

Compare bids on the same system and thickness, how it attaches, how parapets and drains are detailed, insulation, and warranties. If torch-down is proposed, ask what fire precautions the crew follows and whether a torch-free alternative suits the edges. For your actual price, request a free written estimate: a licensed roofer measures the roof and prices your exact scope.

Related: what drives roof replacement cost, roof size estimator, dry rot and decking, quote checker.