Ice can also accumulate to a considerable depth. These loads must be considered in calculating deflections and differential movements. In shading the building's interior from the sun, the roof itself is exposed to solar radiation. Roof materials must be selected and assembled to control conduction, convection and radiation and thereby limit energy consumption to an acceptable level. Daily and seasonal temperature variations in the roof components themselves will affect their performance over time.
Materials have different coefficients of thermal expansion and contraction.
Differential movement between components and thermally induced stresses within materials, if not allowed for in the design and construction of the roof, can cause tearing, bending, loss of securement and ultimate failure of the roof. Air Movement Interruption of the laminar flow of wind as it blows over and around a building results in turbulence and areas of positive and negative pressure. This is sufficient force to scour gravel ballast, flip concrete pavers and peel off membranes that are inadequately secured. Keeping a roof on a building is no small task. Air flow through a building envelope can carry with it significant amounts of heat and moisture.