Adhered and mechanically fastened systems are intrinsically lighter in weight. Some sheet membranes have the capability of being factory seamed by the manufacturer into very large panels, effectively reducing the number of seams that must be completed in the field. This can be significant from the standpoint of both economy and quality control during installation. This approach is suitable primarily when there are large uninterrupted expanses of roof surface to be covered. If there are many penetrations on the roof or odd shapes, planes and angles, working with an oversized sheet can be cumbersome and eliminate any advantages that might have been realized.
Structural integrity is always an issue in reroofing situations.
The condition of the existing deck should always be investigated before the new roof system is designed. The most important climatic variable that affects roof system design is wind. Wind pressure is a result of wind speed, building height, location and surrounding terrain, and any peculiar structural conditions that might exist. Buildings subject to high wind pressures may not be suitable candidates for ballasted roof systems unless special precautions are taken to ensure that the ballast will stay in place. Other climatic variables include exposure to ozone, ultraviolet light, rapid thermal changes and temperature extremes.