Flat Roof Rainwater Drainage Calculations

Anyone can begin the process of turning a home or business green by making and installing a basic rain barrel.

Flat roof rainwater drainage calculations.

The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout. The system outlined below will walk you through the steps of determining your rain barrel sizes based on average roof runoff. Sizing a roof water drain. The result is the number of drains needed.

The number of roof drains shown should be verified with local code requirements. The above sizing data is offered as a guide only. Poor drainage can lead to serious issues with flat roofing from leaks to structural damage. The first step in sizing a roof drain is to calculate the surface area of the roof that the drains will be covering as well as the average hourly rainfall rate at the building location.

Take the roof s total square footage and divide by the total square footage handled by one drain. I downloaded installed and tried out harmer drainage s free roof drainage calculator for a flat roof choosing a roof drain product line which has implications of drain pipe diameter and thus capacity geographic area the tool can plug in rainfall rates for the u k and i used an assumed a roof area of 10x10m 100 m2. In sizing roof drains and storm drainage piping one half of the area of any vertical wall that diverts rainwater to the roof shall be added to the projected roof area for inclusion in calculating the required size of vertical conductors leaders and horizontal storm drainage piping. This reveals that the minimum size for the leader pipe is 5.

The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. The angle is not significant enough to prevent water from pooling on the surface. Calculate drains needed. A simple rain catchment system can provide water for outdoor use resulting in a lower water bill.

For flat roof drainage where you place your drains scuppers and the final material of the roofing is more important. To size the vertical roof drain for the same parameters 5 000 square feet of room area and 6 per hour of rain consult table 1106 2 figure 3. The speed at which the rain collects at the drain. The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.

This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. Unlike other roofing types that are slanted or sloped to allow water to drain automatically flat roofs need a built in drainage system to help remove moisture and debris.