Aftermath of a roof collapse – image courtesy of pixabay.com

A roof collapse can be sudden, dangerous, and devastating. Often, excessive loads can be the cause of a collapse. These loads can be weather related, involving things such as heavy snow or pooling rainwater. Another cause may be improper roof repair, such as failure to remove shingles or tiles when re-roofing or repairing leaks.

Roofs are typically designed to support their own weight (consisting of framing members, sheathing, and roofing materials), plus the weight of expected live loads.  Live loads consist of people who might need to walk on the roof to service equipment or to perform roof repairs, and the estimated weight of ponded rain (if the roofs are flat), and accumulated snow (if the building is in a snow area).  Each of these conditions must be considered in the design of the supporting members.  One problem that is particular to flat roofs is the deformation of roofing support members that can cause water to pond on the roof.  Once the water begins to pond, the framing members deflect more, which leads to more ponding, which leads to more deformation.  An unstable condition is created in these roofs that can eventually lead to collapse of the roof. Continue reading