What does the code say about layering?
California's residential code bans a new roof over two or more existing layers, over water-soaked or deteriorated roofing, and over slate or tile (CRC R908). Many Peninsula homes got an overlay in the 1980s or 90s, so the next roof is a tear-off.
Fog side or bay side?
| Where | What usually fails | Repair or replace? |
|---|---|---|
| Fog belt (Daly City, Pacifica, San Bruno hills) | Moss lifting shingles, corroded flashing | Moss on a young roof can be cleaned; widespread lifting usually means replacement |
| Bayside flats (San Mateo, Foster City, Redwood City) | Sun-worn shingles, granule loss | Granule loss across the roof means it's near the end |
| Foothills (Belmont, San Carlos, Woodside) | Tree damage, clogged valleys | Isolated limb damage is often repairable |
| Low-slope mid-century roofs | Ponding, split seams | Repeated seam failures point to replacement |
How old is too old?
InterNACHI lists 3-tab shingles at about 20 years and architectural shingles at about 30 (InterNACHI). A 1990s roof on a 1965 house is likely due.
When does a repair just buy time?
When the same area leaks again after a repair, or a roofer finds soft decking in several places, money spent on patches is better put toward the new roof.
Every roofer we work with is licensed, insured and highly reviewed by Bay Area homeowners.
Get a free replacement quoteFrequently asked questions
Can moss damage be repaired?
If the shingles are still flat and intact, cleaning and treatment can help. Shingles already lifted or brittle usually need replacing.
Is an overlay allowed on my house?
Only if there's one existing layer in sound condition, and it isn't tile or slate, under CRC R908.
How do I know my roof's age?
Check your purchase disclosures, ask your city building department for past permits, or have a roofer estimate it.
Sources
Sources reviewed November 11, 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.