such as galvanized steel or copper tubing. Branches are usually either threaded galvanized steel pipe with drainage (recessed) fittings or copper tubing.
The stack is sized in the same way as the building sewer. The maximum discharge of the plumbing installation is calculated in drainage fixture units. This figure is applied to table 7-4 or table 7-5 to obtain the proper stack size.
Continuing our example, the 270 drainage fixture units would require a 5-inch stack, if the stack had less than three branch intervals. (No soil or waste stack should be smaller than the largest horizontal branch connected, except that a 4 x 3 water closet connection should not be considered as a reduction in pipe size.)
An offset above the highest horizontal branch is an offset in the stack vent and should be considered only as it affects the developed length of the vent.
An offset in a vertical stack with a change in direction of 45 degrees or less from the vertical
Table 7-4. - Maximum Loads for Soil and Waste Stacks Having Not More Than Three Branch Intervals
piping may be sized as a straight vertical stack. In piping where a horizontal branch connects to the stack within 2 feet above or below the offset, a relief vent should be installed.
A stack with an offset of more than 45 degrees from the vertical should be sized as follows:
1. The portion of the stack above the offset should be sized for a regular stack, based on the total number of drainage fixture units above the offset.
2. The offset should be sized as for the building drain. See table 7-3.
3. The portion of the stack below the offset should be sized as for the offset, or based on the total number of drainage fixture units of the entire stack, whichever is larger. A relief vent should be installed for the offset. Never connect a horizontal branch or fixture to the stack within 2 feet above or below the offset.
The water closet, strictly speaking, has no waste. It is usually connected directly into the stack on a short as possible separate branch of its own by the use of a closet bend. The closet bend is 3 or 4 inches in diameter if made of cast iron or steel and 3 inches if made of copper.
Because lavatories are used for washing hair, loose hair is often carried down into the waste pipe, causing a stoppage. Lavatory drainage is improved by using a minimum number of fittings and by eliminating long horizontal runs. The minimum pipe size for lavatory wastes is 1 1/4 inches, but 1 1/2 inches is more satisfactory.
Urinals present a particular problem because cigarette butts, cigar stubs, chewing gum, matches, and so on are often discarded in them. These materials can easily cause a stoppage. For this reason, urinals should be equipped with an effective strainer. Size of waste pipe should be at least 1 1/2 inches for wall-mounted urinals and 3 inches for the pedestal siphon jet urinal.
Shower wastes seldom cause trouble since they have a relatively clear water waste flowing through them. The usual diameter of the waste pipe for a single shower is 2 inches if made of cast iron or steel and 1 1/2 inches if made of copper.
A domestic kitchen sink requires a 1 1/2-inch cast-iron or steel waste pipe. When a sink is equipped with a garbage disposal unit, a minimum of 2 inches is required for the cast-iron or steel drainage piping.Continue Reading