CSLB C-39 Roofing ContractorSafety and RepairHard
A roofing contractor is preparing to reroof a residential property in California. The existing roofing material is asphalt shingles, and the roof deck is skip sheathing (spaced boards). The client desires a new asphalt shingle roof. Which of the following best describes the most appropriate preparation of the skip sheathing before installing the new shingles?
- AInstall a high-temperature self-adhering underlayment directly over the skip sheathing.
- BRemove the skip sheathing and install a continuous solid sheathing of minimum 1/2-inch plywood or OSB.
- CInstall a single layer of 1/2-inch plywood over the skip sheathing.
- DInstall new 1x4 or 1x6 wood boards to fill the gaps in the skip sheathing.
Show answer & explanationAnswer & explanation
Correct answer: B. Remove the skip sheathing and install a continuous solid sheathing of minimum 1/2-inch plywood or OSB.
Modern asphalt shingles require a continuous, solid deck for proper fastening and performance, as they are not designed to span gaps. Removing skip sheathing and installing continuous plywood or OSB is the correct and code-compliant method for reroofing with asphalt shingles.
Why the other options are wrong
- A. Self-adhering underlayment requires a solid substrate for proper adhesion and bridging; it cannot be applied directly over skip sheathing gaps.
- C. Installing plywood over skip sheathing adds weight and may not fully address fastening issues if the plywood is thin or not securely fastened to solid framing.
- D. Filling gaps with new boards can be done, but it's less ideal than a continuous deck and may not meet all shingle manufacturer requirements for a truly 'solid' substrate.
Skip Sheathing for Asphalt Shingles
When reroofing with asphalt shingles over existing skip sheathing, the skip sheathing must be removed and replaced with a continuous, solid roof deck.
- Asphalt shingles require continuous support.
- Prevents shingle sag and fastening issues.
- Ensures code compliance and manufacturer warranty.
Memory trick: For new shingles, old gaps won't do; rip out the skip, make the deck solid and new.