The answer to 'when to replace roof decking' is that roof decking should be replaced when it shows signs of significant damage or deterioration. Roof decking, also known as sheathing, is the structural layer beneath the roofing materials that provides the foundation for the roof. Over time, the decking can become worn, rotted, or damaged, compromising the integrity of the entire roof system.
Some common signs that it's time to replace the roof decking include visible cracks, holes, or soft spots, water damage or leaks, and excessive sagging or unevenness. In general, if more than 20% of the roof decking is damaged, it's recommended to replace the entire roof system, including the decking, rather than just patching the problem areas.