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?
How long each lasts, per InterNACHI:
| Flat roof system | Estimated life (years) |
|---|---|
| Built-up roofing | 30 |
| Modified bitumen | 20 |
| TPO | 7 to 20 |
| EPDM rubber | 15 to 25 |
What drives the price of a flat roof replacement?
- How water leaves the roof: drains, scuppers, slope
- Perimeter details: parapet walls, curbs, skylights
- Existing layers and deck condition
- Whether insulation is added above the deck
- Access and staging on the lot
Does my flat roof need to be a cool roof?
Low-slope cool-roof rules depend on climate zone: zones 4 and 6 through 15 require them on qualifying reroofs, which includes the South Bay (zone 4) and inland Contra Costa and the Tri-Valley (zone 12). San Francisco, the Peninsula, Marin and bayside East Bay cities are mostly in zones 2 and 3, without a prescriptive rule. See the CEC compliance manual.
What's different about flat roofs in the Bay Area?
Flat roofs cluster in a few places: San Francisco row houses behind parapets, Eichler and mid-century neighborhoods in the South Bay, the Peninsula and Contra Costa, and flat additions and garages everywhere. Each regional guide covers the local version.
| Region | Guide |
|---|---|
| San Francisco | sfroofreplacement.com |
| San Mateo County | sanmateoroofreplacement.com |
| East Bay | eastbayroofreplacement.com |
| South Bay | southbayroofreplacement.com |
Marin and Sonoma flat roofs follow the same rules; homes there are mostly in climate zones 2 and 3.
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.
Every roofer we work with is licensed, insured and highly reviewed by Bay Area homeowners.
Get a free replacement quoteFrequently asked questions
Can a flat roof be recovered instead of torn off?
Sometimes, but California's code bars recovering over two or more layers or over water-soaked roofing, so many Bay Area flat roofs need a tear-off.
Do flat roofs need a permit?
A reroof generally needs a permit from your city or county building department. Ask the roofer to pull it and list the fee.
Are flat roofs common in the Bay Area?
Yes, in San Francisco row houses and in Eichler and mid-century neighborhoods. Flat additions and garages are common everywhere.
Sources
- InterNACHI: life expectancy of roofing materials
- CEC 2025 Single-Family Compliance Manual, ch. 9
- California Residential Code R908 (reroofing)
- CEC: climate zones
Sources reviewed November 12, 2026. Figures are published estimates and official fees, not quotes. Confirm prices, permits and requirements with your contractor and building department. This page is general information, not legal or insurance advice.