Drainage from roofs

Steeply sloped roofs, low sloped roofs, flooded roofs and roof terraces discussed. A perfectly flat roof cannot be achieved in normal construction and slopes will inevitably develop owing to structural deflections. It is better to build in slopes to control water on a roof. The practicable minimum for main roof areas is about 1/4 inch per foot, and greater slope is desirable. Where drainage is achieved by a folded plate type of arrangement, crickets should be placed at the intersection of the larger slopes to direct water to the drains. When controlled flow drainage or evaporative cooling are required on roofs, a sloping roof produces a less hazardous condition than a flat roof. For protected membrane type roofs, the principal membrane at the deck below insulation and landscaping should be sloped, continuous and sealed round all penetrations.