Roof Drainage & Gutters

Drainage of water from the roof is extremely important in order to achieve complete weather-proofing of the building. A well designed water collection system, through set of Gutters and Drain Pipes at eave-end, not only protect property and building but also helps in water harvesting.

Gutters (Figure-14), made out of galvanized metal strips, are installed with a generous slope to avoid water accumulation. To be on safer side, Gutters should have a slope steeper than 1 in 500.Typically, slope on house gutters is maintained at 1 in 250. Design of Gutters and Drain Pipesis based on rainfall intensities (mm/hour) for a given territory along with water receiving area of the roof. “Total Water Receiving area of Roof - TWRR” can be calculated from the plan of the structure. To allow for the slope of the roof, increase the plan area by 1% for every degree of increase in slope up to 40 degree. For a given rainfall intensity and cross sectional area of Gutter, “Total Water Receiving area of a single Drain Pipe (TWRD)” can be calculated from the graph below. The diameter of Drain Pipes considered in the graph is 100 mm. The required number of 100 mm diameter Drain Pipes can be arrived by dividing TWRR by TWRD. An example calculating the required numbers of Drain Pipes is indicated in Figure-15. An illustrative example of Drain Pipe arrangement along with high points of water drainage is indicated below (Figure-16).