What can lead to rafter sag?

Rafter sag is often caused by roof loads that exceed the design capacity of the rafters. When the weight of the roofing materials, along with environmental factors such as snow or ice accumulation, is too great, it can lead to a gradual bending or sagging of the rafters. This is particularly problematic when the rafters are not adequately sized to support the intended loads.

In situations where the structural integrity of the roof is compromised due to excessive weight, the rafters will bow under the pressure, resulting in noticeable sag. Proper engineering and adherence to building codes are critical in determining the appropriate size and spacing of rafters to adequately support the expected loads for a given roofing structure.