Take the roof s total square footage and divide by the total square footage handled by one drain.
Sizing roof leaders.
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.
Calculate drains needed.
This reveals that the minimum size for the leader pipe is 5.
This table is based on zurn s roof drain vertical requirement for horizontal roof areas at various rainfall rates table.
The result is the number of drains needed.
The above sizing data is offered as a guide only.
Sizing a roof water drain.
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.