Foreseeable Failure: Roof Collapses and Roof Drainage Deficiencies

Roof collapses are often catastrophic events, with the potential to devastate property and to endanger the life and safety of building occupants. A common cause of catastrophic roof collapses is inadequate roof drainage and a resulting accumulation of rainwater that exceeds the capacity of the underlying framing. While numerous factors can contribute to inadequate roof drainage, the authors have observed that roof collapses can frequently be traced back to deficient drainage design or the lack of secondary drainage. Secondary drainage considerations are of particular interest because building codes have regressed and no longer directly require that secondary drainage be added to existing structures upon the replacement of the roof system. This paper discusses the authors’ experiences regarding roof collapses caused by inadequate roof drainage. Case studies are utilized to illustrate the implications of inadequate roof drainage and the shortcomings of current building code requirements. Case studies are also presented that indicate the chilling potential for future roof collapses.