The drainage and vent system in Figure 1 is designed in accordance with the Uniform Plumbing Code. The UPC permits many types of venting systems for protecting the trap seal from siphonage (negative pressure) and backpressure (positive pressure).

The plumbing fixtures are vented using vertical wet vents, the most economical venting design. Vertical wet venting is used for all fixtures that connect to a branch vent. The branch vent connects to the vent stack on each floor.

At the base of the drainage stack, a vent stack is required (10 or more branch intervals) to relieve pressures that develop in the drainage stack and terminates to the outdoors. A relief vent is installed at various intervals to assist fixture venting and the venting of the drainage stack. The top of the drainage stack connects to the vent stack and terminates to the outdoors. The type of venting system illustrated in Figure 1 is vertical wet venting.

The drainage and vent system in Figure 2 is designed in accordance with the International Plumbing Code. The plumbing fixtures located in the bathroom group are vented by a vertical wet vent. The clothes washer and laundry tray are vented by a common vent. The kitchen sink is individually vented, as it is not permitted to be vented by a vertical wet vent. Only fixtures located with a bathroom group can be vented by a vertical wet vent.

Each wet vent, common vent and individual vent terminate to air admittance valves. At the base of the drainage stack, a vent stack is required (at five or more branch intervals) to relieve pressures that develop in the drainage stack and terminates to the outdoors. Stack type air admittance valves are not permitted to serve as a vent terminal for vent stacks or stack vents that serve drainage stacks having more than six branch intervals. A relief vent is installed at various intervals to assist fixture venting and the venting of the drainage stack. The top of the drainage stack connects to the vent stack and terminates to the outdoors.

Table 1 supports the conventional wet venting method in Figure 1 as the superior, more cost-effective and economically feasible design method without the use of air admittance valves. Because air admittance valves have moving parts, access and maintenance are required for replacement. Negative and positive pressure, extreme temperature variations and corrosive vapors affect the operation of an air admittance valve, thereby introducing sewer gases into the building. An open piping system regulates the pressure with air from outside the building while air admittance valves regulate the pressure inside the venting system with air from inside the building.

As shown in Figure 1 and Figure 2, both systems require vent stacks and relief vents. The installation of the kitchen sink vented by a vertical wet vent method in the UPC is more cost effective, thereby minimizing the cost of additional drainage and vent piping. As noted above, the drainage and vent stack are run vertically to minimize the piping to the fixtures on each floor. The branch vent as shown in Figure 1 is near the vent stack, thereby minimizing the length of pipe. The additional costs of the IPC venting design method include the air admittance valves for fixtures, accessible valve boxes, firestopping penetrations for each valve box, and drainage and vent piping for the kitchen sink, which far exceed the cost of a branch vent. RJ 2.0