How do you repair roof decking?
Short answer. Roof decking is repaired by removing the shingles and underlayment over the damaged area, cutting the rotted plywood or OSB back to the center of the nearest rafters, and fastening new sheathing of the same thickness with proper gaps and nailing. The roof is then rebuilt with new underlayment and shingles, and the cause of the rot, usually a leak or poor ventilation, has to be fixed too.
Signs decking needs work
Spongy spots underfoot, a visible sag between rafters, dark staining or daylight seen from the attic, and delaminating plywood or swollen OSB edges. In Georgia, decking along the eaves often rots first when overflowing gutters let water wick back under the drip edge.
The repair
- Strip shingles and underlayment a little beyond the soft area.
- Cut out the bad sheathing so the new panel's edges land on the center of rafters or trusses. Set the saw depth to the decking thickness to avoid cutting framing.
- Check the rafters for rot; sister or replace damaged ones.
- Install new sheathing that matches the old thickness, commonly 7/16 inch OSB or 1/2 inch plywood on Georgia homes, leaving about a 1/8 inch gap at edges for expansion. Use panel edge clips between rafters where the span calls for them.
- Nail with 8d nails, typically every 6 inches along supported edges and every 12 inches in the field, or as your local code requires.
- Rebuild with new underlayment and shingles, weaving into the existing courses.
During a replacement
Most decking problems are found only when the old roof comes off. A good contract lists a per sheet price for replacement decking so nobody is surprised. In an insurance claim, decking damaged by the covered loss or required by code is often included, so ask the roofer to photograph every bad sheet.
Compare OSB vs plywood decking and ventilation basics.