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Planning For Thermal Movement

The builders of the St Louis Gateway Arch overlooked thermal expansion. Do you? It could lead to roof leaks and other problems.

It was October 28, 1965. A huge ceremony was planned to celebrate the “topping out” of the colossal stainless-steel monument. The St. Louis elite gathered to watch the keystone be inserted, but nobody expected what happened next. The morning sun had heated the metal so much, it had expanded much more than anticipated. In fact, the keystone was a full five inches too long to set in place. Fortunately, a solution was hit upon and water was sprayed on the south leg of the monument until the surface cooled enough to insert the stone.

Fast-forward to today. The metal roof you are installing may not be as spectacular as the Gateway Arch, but it is just as important to the building or home owner—whether that’s you or your customer. The problem is, much like the arch designers did, it’s easy to overlook planning for thermal expansion and contraction.

The issue is rigidity. As with all rigid materials, metal expands and contracts when temperatures change. To be precise, the amount of thermal movement is a function of the panel’s length, the magnitude of the temperature change, and the coefficient of thermal expansion specific to the type of metal.

The most obvious thermal expansion and contraction is with standing-seam systems. In these types of roofs, long panel runs can exceed 100 feet. In climates where the diurnal temperature change can swing greatly — such as 100 degrees — a 120-foot-long piece of steel sheet metal can expand and contract more than 1 inch in length.

Not all thermal movements are so obvious. But while the movement may be small, it is not insignificant. Failing to plan for thermal movement, regardless of the size, increases the possibility that your metal roof system will fail. Metal components can distort and loosen from substrates. The movement can pull out screws, elongate holes in panels, and cause panels to shift or bend. Compromising your roof like this can lead to leaks and make your roof more vulnerable to storm and wind damage. For building owners, this is an expensive hassle. For contractors, this could be a reputation-damaging event and a profit-draining claim or callback.

Proper design and installation is essential to avoid these hassles and ensure a roof system that performs to spec. Using hidden clips and other attachment techniques, you can allow for thermal movement while preventing wind uplift. Ask your manufacturer or dealer about the proper methods to account for thermal movement. It will save you plenty of headaches (and leaks) in the future.