What is roof decking, and what is dry rot?
Under every roof is a deck: plywood, OSB or wood boards. When water keeps getting in, fungal decay turns it soft and weak, which roofers call dry rot. Older shake roofs often sit on spaced boards with gaps between them rather than a solid deck.
What does the code require under a new roof?
Under CRC R905.2.1, asphalt shingles must be fastened to wood structural panels or solid lumber sheathing. Spaced boards get covered or replaced, and rotted wood must go, because new roofing can't be fastened securely to it.
What are the signs of decking problems before tear-off?
- Dips in the roof plane
- Attic sheathing that is stained, dark or delaminating
- Repeated leaks in one area
- Moss, needles or ponding water that never dries out
How is decking priced in a contract?
Protect yourself with a stated decking unit price, photo documentation of replaced sheets, and a written change order for anything beyond the contract, as California law requires (B&P 7159.6). For your actual price, request a free written estimate: a licensed roofer measures the roof and prices your exact scope.
Where does decking rot show up in the Bay Area?
Where decking problems concentrate depends on the region: foggy, shaded coastal and hill areas (San Francisco's west side, the Peninsula fog belt, Marin, west Sonoma County) see more rot; pre-war cities (San Francisco, Oakland, Berkeley) more board and spaced sheathing; shake country in Sonoma and Napa the shake-to-solid-deck conversion; and Eichler neighborhoods tongue-and-groove decks that are also the ceiling. Regional guides:
Related: what drives roof replacement cost, roof size estimator, repair or replace, quote checker.
Every roofer we work with is licensed, insured and highly reviewed by Bay Area homeowners.
Get a free replacement quoteFrequently asked questions
What is skip sheathing?
Spaced boards with gaps between them, typical under old wood shake roofs. Shingles need a solid deck, so it's covered or replaced.
Should decking be in the written contract?
Yes: a unit price, how replaced sheets are documented, and written change orders for extra work.
Where in the Bay Area is roof decking rot most common?
In damp, shaded and foggy areas, and on older homes with board sheathing. Dry inland areas see it mostly around old leaks.
Sources
- California Residential Code R905 (roof coverings)
- Business and Professions Code 7159.6 (change orders)
- 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.