An inch of rain is not much but it if falls in half an hour it could flood a gutter.
Roof drainage calculations flat roof.
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.
The full flow capacity of a drain is not realized until the water reaches approximately 2 5 above the inlet in a four inch drain and 3 5 in a six inch drain.
This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table.
Gather some basic weather information to calculate the proper size for gutters and downspouts for a house.
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.
Size vertical storm drainage piping.
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.
The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.
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.
Upon completion a full set of rainwater drainage design calculations are provided confirming the suitability of products.
How to calculate the quantity of drains required.
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.
Total roof area also affects runoff.
Calculate drains needed.
Size horizontal storm drainage piping.
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.
2 estimate the roof drain outlet size you will likely use.
4 roof drain 3 determine your building s location on the above map to determine the approximate rainfall as measured in inches.
The sizing of roof drains must be large enough to quickly carry away all.
Appendix b in the ipc provides rates of rainfall for various u s.
The above sizing data is offered as a guide only.
Factors which affect proper roof drainage are deck slope drain size and placement of drains.
Cities based on inches per hour that may fall during a storm of one hour duration and a 100 year return period.
Select number of roof drains and calculate the roof area sloped to each drain.
The total rainfall and how rapidly it falls will affect the runoff from the roof.
The result is the number of drains needed.
For the purposes of this appendix the following metric conversions are applicable.
