We use a two part glazing bar on our canopies with rubber gasket or cushions to attach the roof polycarbonate sheets as this allows for the expansion of the sheets as the weather heats up or cools down. The rubber gaskets as well as creating a watertight seal greatly reduce noise levels as the sheets expand and contract. We do not screw sheets directly to the framework as this can lead to the roofing sheets buckling and potentially causing leaks due to the possibility of screw heads popping off. In addition to this we never lap one sheet over the other as this can result in an algae build-up resulting in unsightly discoloured patches in the roof.