What is roof decking rot?

Roof decking rot refers to the deterioration of the plywood or OSB sheathing that sits below roofing materials. When water penetrates through damaged shingles, flashing failures, or ice dams and soaks into the decking layer, moisture creates conditions for fungal growth and wood decomposition. This decay weakens the structural support system that holds the roof up and distributes loads across the home's frame.

Inspectors identify roof decking rot through several methods. During a visual inspection from the attic, they look for soft spots or spongy areas where the sheathing has lost its rigidity. Water stains, dark discoloration, or visible mold indicate moisture problems. More advanced inspection techniques include moisture meters to measure water content in the wood and thermal imaging to detect moisture pockets that may not be visible. In severe cases, areas of the decking may need to be probed or partially removed to assess the full extent of decay.

Rot matters because it affects both safety and expense. Compromised decking can sag or fail under the weight of the roof itself, especially during heavy snow loads common in Georgia winters. Once rot starts, it spreads quickly through the plywood grain, and affected sections must be cut out and replaced as part of a larger roof repair. Catching it early through routine inspections prevents structural damage and keeps replacement costs manageable. Georgia contractors performing roof repair work frequently encounter this issue in homes with aging roofs or prior water intrusion problems.