Preparing a deck for asphalt shingles is a crucial step to ensure the roof performs well over time. The deck, typically made from plywood or oriented strand board (OSB), must be solid, flat, and securely fastened to the roof framing before shingles are installed. Good flatness is essential because bumps, dips, or uneven spots can create weak points where shingles may crack or wear prematurely. To check flatness, stand on the deck and look for any obvious unevenness, or use a long straightedge to find high or low spots greater than 1/4 inch over 10 feet, which might require sanding or adding a new layer of sheathing. All deck panels should be fully attached with corrosion-resistant fasteners like nails or screws, spaced according to code and manufacturer guidelines—typically every 6 to 8 inches along framing members. Loose or improperly fastened panels will allow unwanted movement underfoot, increasing the risk of shingle damage and leaks.
You can safely check these basics yourself by walking on the roof deck and inspecting for squeaks, loose panels, or noticeable dips. Also, check the edges where panels meet; gaps wider than about 1/8 inch may need filling to prevent water intrusion and maintain shingle integrity. However, diagnosing issues beyond surface checks—such as the decking’s structural soundness, moisture damage, or alignment with manufacturer warranty requirements—is best left to a professional roofer. When calling a contractor, ask how they will verify deck flatness and what type of fasteners they intend to use. Clarify whether they will use code-approved plywood or OSB sheathing suitable for asphalt shingles, as some warranties require specific materials and fastening patterns for coverage to remain valid. This will help ensure a long-lasting, secure roof installation without surprises.