THERMAL EXPANSION AND CONTRACTION
When metal is subjected to a change in temperature, it responds by changing size, known as thermal expansion and contraction. An increase in temperature makes the member bigger and a decrease in temperature makes the member smaller. For metal panels, change in length is the significant concern. The change in length is proportional to both the original length, the change in temperature and the response characteristic of the metal.
Δ Length (in inches) = Length (in inches) * Δ Temperature (in °F) * ε (in / °F).
Each metal has its own response characteristic, ε, known as the coefficient of thermal expansion. ε for steel is 0.0000065 / °F. For aluminum, ε is 0.0000128 / °F.
A 100’ long steel panel experiencing a 100°F temperature change will increase in length by 0.78”; while an aluminum panel of the same length experiencing the same temperature change will increase in length by 1.56”.
For metal panels, an endlap is considered to be a rigid attachment, so that the total considered length of a panel is the sum of the lengths of the panels attached by endlap.
The lowest temperature that a panel will experience is approximately equal to the lowest air temperature that the panel is exposed to. The highest temperature that a panel will experience is significantly greater than the highest air temperature that the panel is exposed to. This greater temperature is due to the continual absorption of solar energy through daylight hours. The amount of energy absorbed is a function many factors including: climate, building geometry, shading and reflectivity of the panel surface.
Direct fastened panel systems are commonly limited to 60’ to 80’ runs. The change in panel length can affect the fasteners by working them loose or by slotting the fastener holes. The stiffness of the support system can also affect the fastener / panel interaction.
Many standing seam panel systems can accommodate 150’ runs or greater. Standing seam systems have a clip attachment mechanism that accommodates the thermal movement of the panel without damage. Standing seam roof systems must be attached to the building with a fixed point, a point where the roof does not move relative to the support framing. This fixed point is commonly located near an end of the panels – either at the eave or ridge. The other, free end of the panels will experience the maximum amount of thermal movement.
About Metal Sales
Metal Sales Manufacturing Corporation is the premier nationwide provider of metal panels for the construction industry. Metal Sales works with architectural specifiers and commercial construction professionals to create inspirational design solutions. With the industry’s largest and most knowledgeable sales and technical support team, Metal Sales has the expertise to address today’s challenges in high-performance, sustainable and Net-Zero building. Metal Sales has outreach around the world. Delivering outstanding roof, wall and fascia metal panels from its 21 facilities throughout the U.S.