Roof Drainage Calculations Flat Roof

The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.

Roof drainage calculations flat roof. For the purposes of this appendix the following metric conversions are applicable. The sizing of roof drains must be large enough to quickly carry away all. 1 calculate the roof area to be drained. The result is the number of drains needed.

This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table. Appendix b in the ipc provides rates of rainfall for various u s. Roof area is 200 x 500 100 000 sq. 1 in 25 4 mm 1 ft 305 mm 1 ft2 0 0929 m2 100 0 figure a101 1 example roof plan 4 a 101 2 solution.

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. How to calculate the quantity of drains required. Size vertical storm drainage piping. 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.

Take the roof s total square footage and divide by the total square footage handled by one drain. Roof drain system and size the scuppers denoting the required head of water above the scupper for the structural engineer. Total roof area also affects runoff. Size horizontal storm drainage piping.

That calculation is rather easy as it is based on a severe storm and the rainwater flow rate from the roof surface to the roof drain. Factors which affect proper roof drainage are deck slope drain size and placement of drains. Gather some basic weather information to calculate the proper size for gutters and downspouts for a house. The tools guide the user step by step allowing fast and simple roof drainage design whilst ensuring full compliance with bs en12056 3 rainwater drainage design standard.

4 roof drain 3 determine your building s location on the above map to determine the approximate rainfall as measured in inches. 2 estimate the roof drain outlet size you will likely use. Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period. I have found that microbursts five minute storm 10 year return period are sometimes more controlling in the sizing of the roof drainage system than a 100 year storm.

Select number of roof drains and calculate the roof area sloped to each drain. Calculate drains needed. The above sizing data is offered as a guide only. Upon completion a full set of rainwater drainage design calculations are provided confirming the suitability of products.