But this isn t the whole story.
Roof drain conductor sizing.
Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.
Take the roof s total square footage and divide by the total square footage handled by one drain.
Calculate total roof area.
Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain.
The result is the number of drains needed.
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.
Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.
The sizing of roof drains must be large enough to quickly carry away all water entering the roof drains.
This reveals that the minimum size for the leader pipe is 5.
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.
From figure 1108 4 the 100 year 60 minute precipitation is 3 75 inches per hour.
Factors which affect proper roof drainage are deck slope drain size and placement of drains.
Select a reference of a roof drain size with hourly rainfall together with the roof area square footage you have estimated and then determine from the chart below how many roof drains you require.
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.
Or 12 drains required.
The flow rate in storm drain piping shall not exceed that specified in table 1106 2.
Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.
The sizing for the horizontal piping is based on the pipes flowing full.
The flow through the roof drain is very efficient directing the water into the drain.
The end result is roof drains 6 in.
As it turns out the opposite is true of most roof drains.
Or smaller in size have the ability to flow more water to the piping than the piping can handle using 33 for the vertical and full flow for the horizontal.
When sizing roof drains the limiting factor for the amount of water each drain will carry away is the size of leader therefore increasing leader size decreases the number of drains required.
Step by step sizing of zurn drains step 1 a.
1 inch 25 4 mm 1 foot 304 8 mm 1 gallon per minute 3 785 l m.
50 000 4 400 11 36.
To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this.
2 500 4 x 3 75 2 344 sq ft.
4 to avoid severe hydraulic jump and or backpressure good engineering practice requires the vertical leader transition into a larger size horizontal storm drain per the gpm flow indicated in table 2 for 1 8 and 1 4 sloped storm drains.
