The answer to 'why is my fascia sagging' is that the fascia board, which runs along the edge of the roof, has become loose or damaged, causing it to sag. This is a common issue that can be caused by a variety of factors, including weather damage, poor installation, or simply the natural aging of the materials.
Some common symptoms of a sagging fascia include visible gaps between the fascia and the roof, water damage or staining, and the fascia pulling away from the roof or gutters. If left unaddressed, a sagging fascia can lead to further damage to the roof and even the interior of your home.