Thermal expansion and contraction in metal roof systems
As Mother Nature changes moods, it’s critical to understand that metal roof panels, like many other materials, expand when heated and contract when cooled, but the structure they are attached to will expand and contract at a different rate. This difference in expansion and contraction rates must be accounted for in the design and installation of a metal roof system.
The amount of movement by the metal panels depends on the metal type, panel length and temperature change. Because roofs experience wide daily temperature swings, understanding how each metal moves and how to accommodate this movement is key to long-term performance and minimizing popping, oil canning or fastener stress.
Note: Popping sounds do not typically indicate a defect or failure of the metal roof system. The popping sounds typically dissipate over time as the panels go through their expansion and contraction cycles, and the system settles into the up-and-down pattern of the local environment’s temperature range.
Metal type matters
Aluminum will expand and contract almost twice as much as steel. For every 100°F temperature swing, a 30-foot aluminum panel could move about 7/16 of an inch, while a similar steel panel might move only about one quarter inch. Smaller daily temperature swings cause less expansion and contraction, but will still apply stress on clips, fasteners and panel seams.
Best practices for design and installation
Understanding and accounting for thermal movement is essential for the longevity and performance of metal roof systems. By selecting appropriate materials, designing for movement and following best installation practices, issues such as popping sounds, fastener stress and oil canning can be minimized.
Contact your Petersen sales representative or technical service team for guidance on specific projects.
