What is roof decking?

Roof decking, also called sheathing, is a continuous panel layer typically made from plywood or OSB (oriented strand board) that sits directly on the roof rafters. It forms the structural foundation that holds shingles, felt, synthetic underlayment, and other roofing materials in place.

In Ontario homes and commercial buildings, roof decking is critical because it distributes the weight of roofing materials, snow load, and foot traffic evenly across the framing. Without a solid decking base, shingles and underlayment have nothing solid to anchor to, and the roof system becomes vulnerable to wind damage and leaks.

The thickness and grade of decking matter for durability. Standard residential roofing typically uses 1/2-inch or 5/8-inch plywood or OSB. The decking must be properly fastened with nails or screws spaced according to manufacturer and building code specifications. Poor installation, gaps between panels, or rotted decking from water damage will compromise the entire roof system.

During roof replacement or inspection, contractors examine decking for rot, soft spots, or deterioration caused by moisture. If decking is damaged, it must be replaced before new shingles are installed. This is why professional roof contractors always inspect the deck condition as part of their assessment.