The answer to 'roof decking sagging' is that the roof decking, which is the structural layer beneath the roofing material, has become weakened or damaged, causing it to sag or dip. This can be caused by a variety of factors, including water damage, structural issues, or simply age and wear.
Some common symptoms of roof decking sagging include visible dips or depressions in the roof, cracks or splits in the decking, and even leaks or water stains. If left unaddressed, sagging roof decking can lead to further structural damage and even roof collapse, so it's important to address the issue as soon as possible.