Panels Retracted in Cold Weather:
When metal roofing material is installed in cold temperatures it is retracted. The dimension that we are concerned with is the length. The width of the panel is not wide enough to produce any significant expansion. (for more on this, and the prevailing mathematical error, see myths of expansion and contraction)
Panels Expanded in Hot Weather:
In the hot weather the roofing material is fully expanded.
Incorrect Installation:
The illustration on the right shows a metal roof installed with clearance provided for contraction. However, this roof has been installed in cold weather and the material is already contracted.
Result of Incorrect Installation:
When the roof is exposed to higher temperatures it will expand. In modern roofing practice fixed cleats are fastened at the top of the roof allowing expansion to be directed away from the peak. Now, in this situation, the roof will come loose at the edge making it succeptible to wind uplift.
Incorrect Installation:
In the opposite situation a roof is shown to be installed in hot weather. In this example no consideration was given to expansion and the panel was secured snugly to the deck of the roof at the edge.
Result of Incorrect Installation:
Because the roofing panels were installed in the heat they were already expanded. When they are exposed to the cold they will contract. With no room to do this they will distort and pull away from the edge. This also makes the roof insecure and succeptible to wind uplift.
