Thermal Movement
Thermal Movement is the term to simply describe the fact that metal moves! Metal can grow and shrink depending on the elements surrounding it. This is a significant effect to consider when working with a metal building and especially a metal standing seam roof system. If you simply put a screw through a roof panel into a purlin, the constant expansion and contraction of the metal would force the hole through the roof panel to grow and would very quickly create a leak.
This event is solved with a standing seam roof system because of a key element, the "floating" concealed fastener, or "clip". This clip is made of two separate parts. The base remains stationary as it is attached to the purlin or other substrate. The actual clip itself, that is inside of the seam, is attached to the base on a set of tracks that allows it to slide or "float". This small amount of motion is enough to accommodate for the thermal movement that will occur.
One end of the roof panel will always be attached to the building. Either at the eave of the roof or at the peak, the panel will be firmly attached to the building itself. If it wasn't, the clips would simply allow the roof panels to slide completely off of the roof! While one end is held stationary, the other end of the panel is allowed to grow and shrink with the thermal movement occurring under the ridge cap or rake trim. Having the movement take place under another covering will easily prevent leaks.