Copyright Goodheart-Willcox Co., Inc. 318 Section 3 Plumbing System Design and Installation The sketch shows the standpipe for a clothes washer installed above the concrete floor. This arrangement provides more flexibility to modify the location of the standpipe at some future date. However, the standpipe must always be secured to the wall or otherwise sup- ported. Another alternative is to connect the standpipe to the 2″ horizontal drainpipe below the concrete floor using a 2 × 2 × 1 1/2 wye. This type of installation pro- vides more support for the standpipe and permits the cleanout to be installed below the sanitary tee that con- nects the laundry tub to the stack. The sketch shows P-traps at the laundry tub and kitchen sink. These P-traps will not be installed until the fixtures are put in place. Short lengths of horizontal pipe (stub-outs) must be installed and capped during the rough-in stage. During the finish stage, these stub- outs will be cut off and trap adapters installed so the P-trap can be joined to the fixture. The P-trap at the base of the standpipe is typically installed during the second rough stage. Figure 21-6 shows the pipe and fittings for the lower portion of the stack. Once enough digging has been done to install the 2″ long radius 90° ell, work can begin on the stack. If the standpipe is installed as shown in the drawing, the P-trap should be near the concrete floor once it is poured. Given this and knowing where the top of the finished floor will be makes it possible to locate the sanitary tee for the standpipe. Begin by determining the distance from the bottom of the P-trap for the standpipe to the centerline of its out- let. Also, measure the distance from the bottom of the sanitary tee to the centerline of its inlet, Figure 21-7A. For this example, assume that distance A is 4 5/8″ and B is 3 5/8″. Since the P-trap is to rest on top of the con- crete floor, the centerline outlet of the P-trap must be 4 5/8″ above the finished concrete floor, Figure 21-7B. Calculate the total fall for the 2′-6″ length of pipe that will join the P-trap and sanitary tee, Figure 21-7C. The total fall for the 2′-6″ pipe is 5/8″ (2-1/2′ × 1/4″ per foot = 5/8″). Since the sanitary tee inlet must be lower than the P-trap outlet, subtract the 5/8″ fall from the cen- terline height of the P-trap to determine the height of the sanitary tee above the footing (8 5/8″ – 5/8″ = 8″). Check the position of the long-turn ell. Hold the san- itary tee in the correct position and measure the dis- tance from the face of the long-turn ell to the face of the sanitary tee. For this example, assume this dis- tance is 4 1/2″. The appropriate fitting allowance must be added to this face-to-face measurement before the pipe is cut to length (4 1/2″ + 1″ + 1″ = 6 1/2″). Test fit the ell, the length of pipe, and the sanitary tee, and use them to help determine the length of the pipe needed to join the sanitary tee for the laundry tub to the stack. The inlet for the second sanitary tee (connecting a laundry tub to the stack) can be located in a simi- lar fashion, Figure 21-8. According to the rough-in di- mensions for the laundry tub, the stub-out must be 12″ above the finished floor. An allowance for fall must also be taken into account for this installation. If the dis- tance from the stack to the 90° ell is 3′, the allowance for fall is 3/4″ (3′ × 1/4″). The height of the inlet of the sanitary tee should be 11 1/4″ above the finished floor 10uni2033 4″ To building sewer 3° 45⁄8uni2033 2°-6uni2033 String line for top of concrete floor To kitchen Dirt floor 4uni2033 C.O. Standpipe Stack Stub cut for laundry tub Stake Goodheart-Willcox Publisher Figure 21-6. Pipe and fittings for lower portion of stack serving the laundry sink (left) and the washing machine standpipe (right).