expressed in drainage fixture units, would be calculated as follows from table 7-2.

After calculating the total discharge and determining the slope of the piping and the velocity of flow, select the correct size of pipe by using table 7-3. Assume that the cast-iron house drain to be installed will have a slope of 1/4 inch per foot. From table 7-3, the minimum size pipe for the horizontal sanitary drainage system under discussion is 5 inches.

Table 7-3 is for cast-iron soil pipe or galvanized steel pipe house drains, house sewers, and waste and soil branches. When copper tubing is used, it may be one size smaller than shown in the table. Note that the size of building drainage lines must never decrease in the direction of flow.

When provision is made for the future installation of fixtures, those provided for must be considered in determining the required sizes of drainpipes. Construction to provide for such future installation should have a plugged fitting or fittings at the stack to eliminate any dead ends.

Sizing Stacks and Branches

The term stack is used for the vertical line of soil or waste piping into which the soil or waste branches carry the discharge from fixtures to the house drain. A waste stack carries liquid wastes that do not contain human excrement; a soil stack carries liquid wastes that do.

Most buildings do not have separate soil and waste stacks. A single stack known as the soil and waste stack, or simply the soil stack, serves to carry both soil and waste material. Soil stacks are usually made of cast-iron pipe with caulked joints. They may, however, be made of other materials

Table 7-3. - Maximum Loads for Horizontal Drains