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What does dry rot or decking repair add to a roof replacement in the South Bay?

Short answerAnywhere from a little to a lot. After tear-off, a South Bay roofer may find a few soft sheets or a whole deck that can't hold new roofing. Insist on a unit price for replacement decking in the contract, and get a free written estimate before work starts.

Every roofer we work with is licensed, insured and highly reviewed by Bay Area homeowners.

Updated · Sources reviewed November 12, 2026 · By South Bay Roof Replacement

  • Active C-39 roofing license, checked on CSLB
  • Contractor's bond and workers' comp on file
  • Tear-off, permit and warranty paperwork handled
  • Free written estimate, no obligation

What is roof decking, and what is dry rot?

Sheathing is the structural layer under the roofing: plywood or OSB on most newer homes, boards on many older ones. Rot sets in when wood stays wet long enough for fungi to break it down. Spaced (skip) sheathing is gapped boards, which suited ventilated shake roofs.

What does the code require under a new roof?

California's Residential Code requires asphalt shingles to be fastened to wood structural panels or solid lumber sheathing (CRC R905.2.1), so spaced boards need plywood or OSB over or in place of them before shingles go on. Rotten sheathing has to be replaced because it won't hold nails.

What are the signs of decking problems before tear-off?

  • A wavy or sagging roofline
  • Water stains in the attic or on ceilings
  • Moss or debris that has sat for years
  • Old leaks that were patched more than once

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 South Bay?

The dry Santa Clara Valley climate means South Bay decks often stay sound for a long time, so rot usually traces to a specific problem: a long-running leak, failed flashing at a wall or chimney, or ponding on a flat roof. Eichlers are the big exception to a plywood deck: many have tongue-and-groove planks that double as the finished ceiling, so damaged boards are a visible interior fix as well as a roof repair. Tile roofs can hide rot under old underlayment until the tiles come off.

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 quote

Frequently asked questions

How much decking will my roof need?

No one knows until the old roof is off. A good bid states a unit price so the extra is predictable.

Should decking be in the written contract?

Yes: a unit price, how replaced sheets are documented, and written change orders for extra work.

Can an Eichler's ceiling boards be replaced from the roof?

Damaged tongue-and-groove decking is the ceiling inside, so replacing it is visible from below. Ask how the roofer matches and finishes it.

Related questions

Sources

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.