Understanding the Dynamics of Thermal Movement in Metal Roofing
Thermal movement in metal roof systems plays a pivotal role in ensuring their longevity and performance. Over the years, roofing contractors have marveled at the craftsmanship of sheet-metal systems from historical structures, some dating back to World War II. The commonality among these long-lasting systems, such as standing-seam, flat-lock, and built-in gutters, is their capability to accommodate thermal movement. When this movement is hindered, the results can be detrimental, leading to failures in a short span of time.
The Science Behind Thermal Movement
At its core, the concept of thermal movement is straightforward, though often overlooked. For instance, a minor ¼-inch expansion in an aluminum panel might go unnoticed by a roofing contractor. Failures stemming from thermal movement can span across multiple thermal cycles or seasons, making them hard to attribute to their actual cause.
Imagine the movement of liquid mercury in a traditional thermometer. As the temperature rises, the atomic particles in the mercury accelerate, leading to its expansion. On the contrary, a drop in temperature slows down these particles, causing the liquid metal to contract.
The rate at which this movement occurs is influenced by the type of metal in use and the temperature of the base metal. Factors such as direct solar radiation significantly impact this process. For instance, the surface temperature of metal roofing materials can vary greatly, being cooler than ambient air temperatures in winter and much hotter in direct summer sunlight. This can result in a temperature change of over 200°F for the base metal.
Key Definitions in Thermal Movement
Accumulated Thermal Movement: This happens when lengths of metal are mechanically attached to one another. For instance, if four 10-foot sections of metal are riveted together, they will expand and contract as if they were a continuous 40-foot section.
Accommodation of Thermal Movement: This is achieved using hook strips, panel clips, or cleats to hold the sheet metal in place. For optimal durability, metal systems should be able to float in at least one direction.
Fixed Points: These are points that anchor the metal to a structure, like roof sheathing. They guide the thermal movement of the metal but don't accommodate expansion and contraction like cleats and hook strips.
Absorption of Thermal Movement: Seen in flat-lock metal systems and across standing-seam panels, this movement is contained within each panel and directed upward.
Flat-Lock Roof Systems
Designed to absorb thermal movement within each panel, flat-lock roof systems have specific design considerations. For instance, copper and stainless steel panels should ideally be 18 by 24 inches. The movement in these systems is absorbed when panels are locked onto hook strips on the roof's perimeter and connected with a flat seam in the field.
Built-In Gutter Systems
Built-in gutter liners, integral to a building's structure, must be made of solderable metals like galvanized steel, stainless steel, or copper. Failures in these systems can lead to significant damage. Proper accommodation for thermal movement is crucial to prevent such failures.
Standing-Seam Roof Systems
Standing-seam systems use raised seams to provide additional strength to metal panels and accommodate thermal movement. These systems are attached with clips, allowing panels to expand and contract vertically.
Underlayment Considerations
Choosing the right underlayment is crucial for metal roofing projects. Not all underlayment types are suitable. For instance, granule-surfaced underlayment can be abrasive to sheet metal during expansion and contraction. It's essential to use underlayment that can withstand high temperatures in metal systems.
In Conclusion
At Unisource Roofing, we pride ourselves on understanding the intricacies of thermal movement in metal roofing systems. As one of the leading roofing companies in Louisville KY, our expertise ensures that your roofing solutions are not only aesthetically pleasing but also durable and long-lasting. Whether you're looking for roof repair in Louisville KY or seeking the expertise of Louisville roofing contractors, Unisource Roofing is here to serve your needs. Remember, while the beauty of metals like copper is undeniable, it's essential to pair them with the right accessories to ensure longevity and performance.