Rainwater Calculation For Roof Drain

Calculator notes and assumptions.

Rainwater calculation for roof drain.

Rainwater collection calculation formulas and equations. 537 section 2 adds an addendum to the swrcb s or state water resources control board s control of water. Factors to be considered in the design of roof drainage sys tems are the area to be drained size of gutters downspouts outlets slope of roof type of building and appearance. Take the roof s total square footage and divide by the total square footage handled by one drain.

Roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember. Plans shall show hose bibs or pump systems for discharge and watering of landscaping. 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 calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain.

Your system will recharge every time it rains so you don t need to estimate. Rain gutters downspouts shall be shown on plans. The result is the number of drains needed. 50 000 4 400 11 36.

Show location of cistern rain barrels. How much water do you need. Dropping from the 5 drain in the table to a 3 drain cuts the serviced or drainable roof area to about 0 26 x the roof areas shown in the table. The rainwater capture act of 2012 2012 california stats.

If you find that your roof will generate an overwhelming amount of water it may be more practical to consider how much water you will need. 1 of rain on 1 000 sf roof will yield 623 gallons. Increasing from the 5 drain shown to a 6 drain increases the roof area that can be served by about 1 6 x the table data. Roof area to be considered the design capacity for a roof drainage system depends on the quantity of water to be handled.

Roof area m2 x precipitation amount mm amount collected liters. The roof area calculation for sizing roof drains is an example of how differences among the codes can challenge the designer. Or 12 drains required. Rainfall wizard is based on table 1 2 rainfall data and drainage factors page 1 2 1 3 of the architectural sheet metal manual 7th edition.

Calculate rainwater catchment volume. Residents are now encouraged to use cisterns and rainwater collection kits to increase the amount usable water that they have on hand. Rain barrels should be designed to store 200 gallons and be located such that roof run off is equally distributed.