Drain pipes shall be sized according to drainage fixture unit (d.f.u.) loads. The size of the drainage piping shall not be reduced in size in the direction of flow. The following general procedure is permitted to be used:
1. Draw an isometric layout or riser diagram denoting fixtures on the layout.
3. Starting with the top floor or most remote fixtures, work downstream toward the building drain accumulating d.f.u. values for fixture groups plus individual fixtures for each branch. Where multiple bath groups are being added, use the reduced d.f.u. values in Table P3004.1, which take into account probability factors of simultaneous use.
Branches and stacks shall be sized in accordance with Table P3005.4.1. Below grade drain pipes shall be not less than 11/2 inches (38 mm) in diameter. Drain stacks shall be not smaller than the largest horizontal branch connected.
|NOMINAL PIPE SIZE |
|ANY HORIZONTAL |
|ANY ONE VERTICAL |
STACK OR DRAIN
|DIAMETER OF |
|SLOPE PER FOOT|
|1/8 inch||1/4 inch||1/2 inch|
|11/2 a, b||—||Note a||Note a|