I believe that the roof area you used in your computation is the projected horizontal area of the roof. Let the roof has its architectural peaks (pointed roofs) as long as you will measure its projected horizontal roof area, that computation will still be in effect. What is your comment about this? If you have a 4 sided roof area and adapting your given roof area value, do the 12 inches can be divided in to 4 pcs-3inches diameter pipe that will be strategically located at each roof corner? What is your comment about this vertical drain distributions. Thanks and keep safe.
Where did .0104 come from? 1 inch of rainfall per hour = 144 (square inches per foot) / 231 (cubic inches per gallon) = .623 (gallons per hour), .623 (gallons per hour) / 60 (minutes per hour) = .0104 GPM Also found on various manufactures charts, such as this one from JOSAM Quality Engineered Plumbing Drainage Products. www.josam.com/images/josammkt/zzother/C07_pgrd7.pdf
Our example is for the vertical drain pipe. Since our rainfall totals 2496 gallons per minute and a 12” vertical drain pipe has a capacity of 3272 GPM per IPC Table 1106.2, we only need 1-12” vertical drain pipe. If your question is asking how many horizontal drain pipes are needed, It would depend on the pipe size selected and the slope. A 4” horizontal drain pipe with a slope of ¼ inch per foot has a capacity of 163 GPM, so 3272 GPM / 163 GPM = 20.07, so we would need 20-4” horizontal drain pipes. A 10” horizontal drain pipe with a slope of 1/8 inch per foot has a capacity of 1311 GPM, so 3272 GPM / 1344 GPM = 2.49, so we would need 3-10” horizontal drain pipes. Vertical leaders are sized based on the flow rate from horizontal gutters or the maximum flow rate through roof drains, not exceeding that specified in IPC Table 1106.3.
While the 0.0104 is correct (it is the inverse of the sq. ft per gallon), the intended method of sizing per 2018 plumbing code was to use the manufacturer's flow rate through drain in order to determine the pipe size.
The intended method of sizing per 2018 IPC was to use the manufacturers’ flow rate through the drain. This is correct. However, per IPC 1106.2 “Size of storm drain piping. Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. The flow rate in storm drain piping shall not exceed that specified in Table 1106.2..” Therefore, we must calculate the flow rate to determine the correct size.
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thank you. Why wouldn't they just put that equation in the code?? The mysteries of the building code....
I believe that the roof area you used in your computation is the projected horizontal area of the roof. Let the roof has its architectural peaks (pointed roofs) as long as you will measure its projected horizontal roof area, that computation will still be in effect.
What is your comment about this?
If you have a 4 sided roof area and adapting your given roof area value, do the 12 inches can be divided in to 4 pcs-3inches diameter pipe that will be strategically located at each roof corner?
What is your comment about this vertical drain distributions.
Thanks and keep safe.
Where did 0.0104 came from?
Where did .0104 come from?
1 inch of rainfall per hour = 144 (square inches per foot) / 231 (cubic inches per gallon) = .623 (gallons per hour),
.623 (gallons per hour) / 60 (minutes per hour) = .0104 GPM
Also found on various manufactures charts, such as this one from JOSAM Quality Engineered Plumbing Drainage Products. www.josam.com/images/josammkt/zzother/C07_pgrd7.pdf
How to calculate drain outlet in kitchen area.
What will be the total number of pipes needed for the roof as per your example?
Our example is for the vertical drain pipe. Since our rainfall totals 2496 gallons per minute and a 12” vertical drain pipe has a capacity of 3272 GPM per IPC Table 1106.2, we only need 1-12” vertical drain pipe. If your question is asking how many horizontal drain pipes are needed, It would depend on the pipe size selected and the slope. A 4” horizontal drain pipe with a slope of ¼ inch per foot has a capacity of 163 GPM, so 3272 GPM / 163 GPM = 20.07, so we would need 20-4” horizontal drain pipes. A 10” horizontal drain pipe with a slope of 1/8 inch per foot has a capacity of 1311 GPM, so 3272 GPM / 1344 GPM = 2.49, so we would need 3-10” horizontal drain pipes. Vertical leaders are sized based on the flow rate from horizontal gutters or the maximum flow rate through roof drains, not exceeding that specified in IPC Table 1106.3.
Thank you ❤
While the 0.0104 is correct (it is the inverse of the sq. ft per gallon), the intended method of sizing per 2018 plumbing code was to use the manufacturer's flow rate through drain in order to determine the pipe size.
The intended method of sizing per 2018 IPC was to use the manufacturers’ flow rate through the drain.
This is correct. However, per IPC 1106.2 “Size of storm drain piping. Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. The flow rate in storm drain piping shall not exceed that specified in Table 1106.2..” Therefore, we must calculate the flow rate to determine the correct size.