Every building needs moisture and thermal protection, Ching explains the performance of roofing materials. Roof structure are built differently, they are either flat or sloped; a sloping roof can shed water away easy, a flat roof requires pipes or a special membrane to drain or evaporate water away. Exterior walls also need protection from the weather. Solid masonry and concrete loadbearing walls use their mass as a barrier to stop water from penetrating inside a structure. Other wall systems such as curtain wall have an “interior drainage system to carry away moisture that finds its way through the facing or cladding.”- Ching B.C.I (7.02)