Figure 3-39.—Soil pipe branches.

Figure 3-39.—Soil pipe branches. condensation freezes when exposed to low temperatures. One way to prevent freezing is to increase the pipe to a size or two larger than the vertical vent passing through the roof; or, install high-lead flashing to provide an insulating pocket of air between the flashing and the end of the main soil and waste vent above the roof. Being open to the heat of the building, the air pocket allows an intermediate warming area for gases leaving the main soil and waste vent. Materials used in vent piping ordinarily include galvanized pipe, cast-iron soil pipe, and at times, brass, copper, and plastic pipe. Asbestos-cement pipe can also be used for venting both soil and waste pipe. A single length of this pipe is often sufficient for venting a stack. For such an installation, pipe is available with a machined end. This end is placed in the bell of the soil or waste pipe, and the connection is made by yarning, leading, and caulking. In all phases of the venting system, do your best to use proper-sized piping. Remember, the diameter of the vent stack or main vent must not be less than 2 inches. The actual diameter depends on the developed length of the vent stack and on the number of fixture units installed on the soil or waste stack. The diameter of a stack vent should be at least as large as that of the soil or waste stack. Both soil and waste pipe BRANCHES are horizontal branch takeoffs that connect various fixtures and the vertical stack (fig. 3-39). One method of installing a branch takeoff from the vertical stack is to use a Y-branch with a 1/8 bend caulked into it. Another method is to use a sanitary tee, which is an extra short pattern 90-degree Y-branch. Of these two methods, the sanitary tee is better because you eliminate one fitting and an extra caulked joint; both are required for the 1/8 bend takeoff. Some local codes allow you to connect more fixture units to a given size of stack when a combination Y and 1/8 bend is used. The combination Y and 1/8 bend may be more desirable than the sanitary tee. Once either fitting is caulked into place, the horizontal branch can be extended as necessary with lengths of soil pipe. They, too, are joined by caulking. Pipes carrying waste should be graded downward to ensure complete drainage. Horizontal vents should be slightly pitched to facilitate drainage of condensation. In this chapter, only the basic types of vents and the locations where they are used have been covered; however, there are many forms of ventilation that can be applied to a plumbing installation. The types of vents used on a project are determined largely by the manner in which the plumbing fixtures are to be installed and where they are located. As plumbers know, the subject of vents is the science of plumbing. Anyone can try to install piping for a plumbing system; however, if the system cannot carry waste away, the would-be plumber and the system are useless. For more information on venting, consult the National Standard Plumbing Code- Illustrated. Q17. Acid-resistant cast-iron pipe is an alloy composed of what two elements? Q18. What is a trap seal? Ql9. To prevent siphonage of seal traps in a plumbing system, what plumbing method should you use? 3-27