What's the difference between TPO and torch-down?
TPO comes in wide rolls of reflective single-ply membrane whose seams are welded with hot air. Torch-down is asphalt-based modified bitumen that the crew melts into place with a torch, usually as a two-ply system. Roofers also install self-adhered or cold-applied modified bitumen, PVC, EPDM, built-up roofs and foam.
How long does each flat roof system last?
Service life differs by system. InterNACHI's chart (source):
| 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?
- Ponding fixes: tapered insulation, crickets, new drains
- Edges and walls: parapet flashing, coping, scuppers
- What's underneath: wet insulation or rotted decking found at tear-off
- Insulation upgrade: often worth doing now
- Getting materials up: stairs, hoists, shared walls
Does my flat roof need to be a cool roof?
The Peninsula cities we checked are in climate zone 3, outside the zones (4 and 6 through 15) where the 2025 Energy Code prescriptively requires a cool roof on a low-slope reroof. See the CEC compliance manual.
What's different about flat roofs in San Mateo County?
Peninsula flat roofs are mostly mid-century: low-slope and flat roofs on 1950s and 60s homes in the San Mateo Highlands, Belmont, San Carlos and parts of Menlo Park, plus flat-roofed garages and additions across the county. Many have little or no attic, so insulation is either above the deck or not there at all, and the reroof is the moment to decide. On the foggy west side, from Daly City to Pacifica, standing water and moss at clogged drains are the common failure points.
How do I choose a system and a roofer?
The right membrane depends on drainage, foot traffic, solar, neighbors' walls and the crew's experience. Get the system, thickness, attachment method and warranty in writing, and for torch-down, ask about fire precautions. 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
How long does a flat roof last?
InterNACHI estimates about 20 years for modified bitumen, 7 to 20 for TPO, 15 to 25 for EPDM and 30 for built-up roofing.
What should a flat roof bid include?
The membrane system and thickness, tear-off, insulation, drains and scuppers, parapet flashing, permit and warranty.
Should I add insulation when I replace a mid-century flat roof?
It's the easiest time to do it, since rigid insulation goes above the deck. Ask the roofer how it affects roof height, flashing and drainage.
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.