Preparing a deck for spray polyurethane foam (SPF) roofing starts with ensuring the sheathing is in good condition and properly installed. The deck should be solid, dry, and free of any debris, dirt, or loose materials that could affect foam adhesion. Plywood or OSB (oriented strand board) sheathing is commonly used, and it must be fastened securely to the roof framing with recommended fasteners like ring-shank nails or screws to prevent movement or squeaks later. The spacing of fasteners is important too; typical specs call for fasteners every 6 inches along the edges and 12 inches in the field to provide a stable surface. Checking for any damaged or rotted sections and replacing them before installation is critical, as SPF cannot seal or fix structural problems. Ensuring the sheathing is dry helps avoid moisture traps under the foam, which can cause rotting or failure over time.
Flatness and smoothness of the deck surface are crucial for a uniform SPF application. Any significant bumps, dips, or gaps in the sheathing will translate into an uneven foam layer, which can compromise insulation performance and roof durability. You can do a simple inspection by running a straightedge across the deck to identify irregularities. Small gaps between sheathing panels (usually about 1/8 inch) are generally acceptable, but wider gaps or raised edges should be corrected—either by sanding, shimming, or replacing boards. It’s safe for a homeowner to visually inspect and report irregularities, but avoid walking excessively on fragile decking. Since installation quality directly impacts warranty coverage and long-term performance, it’s wise to consult a professional roofer experienced with SPF before application. When choosing a contractor, ask specific questions such as: “How do you verify the deck’s flatness before spraying?” and “What fastening pattern and deck material do you recommend for durable foam adhesion?” These help ensure your SPF roof will be installed correctly and last.