This Fremont house still had its original plank decking: rows of narrow boards with gaps between them, the way roofs were built before plywood. Shingle nails can miss the boards or work loose in those gaps. After tear-off, our crew sheeted the entire roof in new OSB right over the planks, so every nail now lands in solid wood. GAF synthetic underlayment went down next, then gray architectural shingles and new ridge caps. The roof was replaced through the homeowner's insurance claim.