Industry Articles & News

What Caused the Roof Collapse?

BACKGROUND:A vacant industrial building was undergoing interior construction during the winter when some of the steel trusses failed and the roof caved in. The current owners purchased the building approximately one year before the failure and had a new roof installed shortly after the purchase date.

SUSPECTS:
Weight of Ice and Snow
Roofing Company Damaging the Roof During Installation
Contractor Damaging the Structure During the Interior Construction
Lack of Proper Roof Maintenance

ASSIGNMENT: Determine the cause of the roof collapse.
Just the Facts: The building in question had a flat roof covered with an EPDM (aka “rubber”) membrane over insulation, metal deck and steel joists. This rubber roof had been installed soon after the building was purchased approximately one year prior to the failure. The building had interior structural steel beam/column framing and concrete masonry unit block exterior walls with steel joists spanning between.
The work being done in the area of the failure was interior partition wall work west of the failure. Snow on the ground around the building was only 3-3.5” deep. There was similar snow depths on the roof along with 1-2.5” of ice accumulation.

At the failed section of the roof joists there were signs of advanced corrosion, deterioration and loss of base metal. No equipment was on the roof at the failed area, however, a review of historical aerial views of this building showed a cluster of rooftop equipment which would have necessitated roof penetrations at this location. This indicated numerous potential sources of prior roof leaks and the current owner confirmed that leaks were the reason for the recent re-roofing.

FINDINGS: The weight of snow and ice did not cause this roof failure. Snow and ice accumulation on and around the building was minimal and well below the building code design roof snow load for this location. A non-damaged roof should have been able to withstand this weight.

The roof collapse occurred due to loss of strength of the roof structure from advanced corrosion and deterioration of the roof joists. This deterioration was consistent with the expected presentation of corrosion from chronic, long-term moisture exposure, likely caused by roof leaks prior to the reported re-roofing of the building.

Since prior repairs were made to these locations of deterioration it is evident that this was an aged condition that the previous owner attempted to address.