The answer to 'why is my ridge vent sagging' is that the ridge vent is likely not properly secured or supported, causing it to sag over time. This can happen due to poor installation, age and wear, or damage from weather and environmental factors.
Some common causes of a sagging ridge vent include insufficient fasteners, inadequate structural support, and deterioration of the vent material itself. Over time, the vent can become loose, allowing it to dip or sag down from the roof's peak. This can lead to leaks, water damage, and reduced ventilation in the attic.