Roof Drain Conductor Sizing

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.

Roof drain conductor sizing. The result is the number of drains needed. Example roof plan 4 a 101 2 solution. Or 12 drains required. 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.

Factors which affect proper roof drainage are deck slope drain size and placement of drains. Table 1106 2 storm drain pipe sizing for si. As it turns out the opposite is true of most roof drains. 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.

From figure 1108 4 the 100 year 60 minute precipitation is 3 75 inches per hour. To convert to an area for a 4 inch per hour rainfall to enter table 1108 1 do this. Take the roof s total square footage and divide by the total square footage handled by one drain. Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow.

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. 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 flow through the roof drain is very efficient directing the water into the drain. Each vertical drain must carry 2 500 sq ft of roof area at 3 75 inches per hour of rainfall.

The next step is to determine each roof area that will be served by a separate leader drain pipe scupper or downspout. Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. But this isn t the whole story. The sizing for the horizontal piping is based on the pipes flowing full.

The sizing of roof drains must be large enough to quickly carry away all water entering the roof drains. 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. 1 inch 25 4 mm 1 foot 304 8 mm 1 gallon per minute 3 785 l m. 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.

Step by step sizing of zurn drains step 1 a. This reveals that the minimum size for the leader pipe is 5. 50 000 4 400 11 36. Calculate total roof area.

Each 4 drain size in a 6 hourly rainfall area will accommodate drainage of 3 070 sq.