Roof sheathing rot — San Francisco, California
Roof sheathing (the plywood or OSB boards nailed to the rafters beneath shingles) can rot when moisture becomes trapped — from a slow leak, poor attic ventilation, or ice dams pushing water under shingles. Soft, spongy spots on the roof surface, sagging between rafters visible from the attic, or dark water stains on sheathing boards are all signs of rot. A roofer can assess the extent of damage, replace affected sheathing panels ($70–$100 per sheet plus labor), and address the moisture source to prevent recurrence.
Why this is common in San Francisco
Winter rains expose roof leaks and drainage failures on the city's steep, hilly lots, while salt-laden fog accelerates flashing corrosion. Flat and low-slope roofs common on multi-unit buildings require specialized membrane maintenance to handle the prolonged wet season.
Who to call
For this problem in San Francisco, call a: Roofer
Find a Roofer in San FranciscoSymptoms to look for
- Soft or spongy spots when walking on the roof
- Visible sagging between rafters when viewed from inside the attic
- Dark stains, mold, or fungus on attic-side sheathing boards
- Shingles that appear wavy, cupped, or dipped in certain areas
Emergency Service in San Francisco
Emergency home services in San Francisco are available 24/7 at premium rates — expect $150–$300+/hour for after-hours plumbing or electrical, the highest tier in the US. Response times average 45–90 minutes given hilly terrain and parking scarcity. Always verify an active CSLB license and proper DBI permits.