In this section, we will discuss the sizing of drainage pipes. We will use a 9 story building residential. Let us define first a new term that will be used frequently and that is drainage fixture unit.

The Uniform Plumbing Code defines Drainage Fixture Unit as follows:

Drainage (dfu). A measure of the probable discharge into the drainage system by various types of plumbing fixtures.

The drainage fixture-unit value for a particular fixture depends on its volume rate of drainage discharge, on the time duration of a single drainage operation, and on the average time between successive operations. – UPC 2006

Drain Fixture Unit, or DFU, is a plumbing design factor, or a relative measure of the drain wastewater flow or load for various plumbing fixtures. Here are two quantitative measures of DFUs:

1 DFU = 1 cubic foot of water drained through a 1 1/4″ diameter pipe in one minute.

1 DFU ≈ (approximately) 7.48 US GPM or ≈ 0.47 liters/second

In a simple way, a fixture unit basically depends on three factors that are

1) Rate of discharge,

2) Time of operation and

3) Frequency of use of fixture.

So based on these factors these tables prepared by ASPE that is the American society of plumbing Engineers, IPC international plumbing code, and UPC Uniform plumbing code.

So I took this table from IPC that is International Plumbing Code and based on this table I am going to do the sizing of drainage piping and as you can see that we have horizontal branch sections given as A, B, C, D is mentioned here in the excel sheet and we are going to calculate the pipe diameter and then we have a vertical stack that is J and then we have offset or run out that is represented by K and another offset run is represented by M.

The list of the fixtures in each branch section is given over here so for example for branch A, we have a water Closet, Urinal, Lavatory, kitchen sink, shower domestic, bathtub, laundry tray, floor drain, and bidet. So according to that we have calculated the fixture unit value from table 709.1 so this is the table fixture unit per fixture or the group so