By Michael Sladki, PE, ECS Mid-Atlantic
"Intense storm creates downpour resulting in roof collapse.” This is not an uncommon headline, and with climate change causing more frequent and stronger storms, it is one that we will continue to see and with greater frequency. Since you can’t stop rain from falling, here are three tips for how to prevent your facility from becoming the subject of a similar news headline.
1) Conduct proactive roof maintenance
Roof maintenance is the best protection owners have to prevent a structural collapse. On a regular basis—ideally monthly—maintenance staff should walk the roof looking for damage, debris and, most importantly, clogged drains.
Area drains on low-slope roofs only function properly when rainwater is allowed to flow, unobstructed, to the drain body to be removed from the roof. When drains become clogged due to debris (leaves, animal droppings, roofing material, etc.), this can lead to ponding.
Verify the roof was properly designed for drainage
While small amounts of water can likely be carried by the roof, certain configurations can lead to an excessive amount of water retention which can overload the structure. Sometimes drainage is as simple as sloping the roof to a gutter system, which overflows when overloaded. In other cases, internal drains are required to remove water from the roof.
International Building Code Section 1502.2 states, “Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.” Primary drainage alone is insufficient; a backup system is required to prevent serious issues.
2) Consult a professional prior to modifying the roof
In some cases, the original design of a roof is sufficient. However, when an adjustment is made to the roof by adding an extension, adjacent building or additional equipment that changes the roof’s performance, unintended consequences may not fully be realized until it is too late.
You don’t have to wait until the roof is being recovered or replaced to conduct analysis. Qualified professionals can assess the roof any time to determine if the design is sufficient for the expected rainfall in your area.
ECS case study
ECS was called upon to assist with the assessment, analysis and repair of a roof collapse after a storm. Upon arrival, ECS’ structural engineers assessed the damage and determined which areas were safe to access and how the structure should be shored to prevent further damage. ECS personnel also accessed the adjacent roof structure to view the damage from above in an attempt to understand why the system failed.
ECS’ initial report indicated that the original roof was a low-slope design with a primary system (gutters on both sides) with a secondary system that allowed for overtopping should the gutters become clogged or overloaded. An adjacent warehouse was built with a higher roof than the original that changed its drainage pattern on that side by removing both the primary and secondary roof-drainage systems.
To compensate, the owner installed area drains in the original roof. Prior to the storm, the area drains were clogged with animal droppings which allowed water to pond and cause a collapse. The roof was not provided with a secondary method of roof drainage to relieve this water pressure prior to collapse.
Subsequent to the collapse, the structure was stabilized, a new roof design was provided and repairs are underway to restore the building’s performance and help ensure that this catastrophe doesn’t recur.
ECS looks forward to helping address your challenges and exceeding expectations on your next project.
Michael Sladki is vice president, principal & engineer at ECS Mid-Atlantic, LLC.