Designer’s Guide Continued from page 14
defined by the UPC. The IPC allows common vents to serve two fixtures of different types and elevation pro- vided that they are on the same floor level, such as a lavatory backed up to a urinal. The IPC has a dedicated siz- ing table for common vents. Wet venting also differs between
the two Codes. The UPC allows verti- cal wet vents only for one and two DFU fixtures, with a maximum of four fixtures and six feet in length. In contrast, the IPC allows both horizon- tal and vertical wet venting for any combination of fixtures in two bath- room groups. The IPC has a dedicated wet-vent sizing table. Horizontal wet venting is quite similar in the two Codes, although the verbiage is differ- ent. The IPC has a dedicated sizing table that represents approximately what the UPC says in words. Circuit venting in the IPC is
roughly the same thing as combina- tion waste and vent as it appears in the UPC. The primary difference between the two is that circuit vent- ing in as-of-right in the IPC, whereas combination waste and vent is only allowed “where structural conditions preclude the installation of conven- tional systems” in the UPC. Translation: Combination waste and vent is up to the discretion of the UPC officials. Combination waste and vent in the
IPC refers to a collection of floor drains and/or sinks (not water closets, showers, etc.) piped together to a hor- izontal drain with one dry vent con- nected at any point within the system. The sizing of the horizontal combina- tion waste and vent pipe has a dedi- cated table in the IPC. Island fixture venting is quite
similar between the two Codes, the difference being that
the UPC
requires the island vent to connect to the horizontal waste below the island, while the IPC requires the island vent to connect to the horizontal waste below a nearby wall. Required cleanouts also vary in location in this same respect. However, while the IPC does not specifically say so in the island fixture section, I would think this to be an ideal application for an air admittance valve. The vent sizing tables differ dra- matically between the two Codes,
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making a comparison somewhat diffi- cult. To give a brief example, in the UPC, a 3" vent stack can carry 84 DFUs and be no more than 212 feet long. The IPC has a sliding scale of length versus fixture units, but to com- pare it with the UPC, a 3" vent 84 feet in length would be allowed almost 190 DFUs — more than double the UPC. The IPC goes on to address the con-
cept of waste stack venting (similar to what is known as the single stack system in Philadelphia) not addressed or allowed by the UPC. This design allows a single stack to serve as waste and vent for fixtures other than water closets and urinals. Again, there is a dedicated sizing chart for waste stack venting in the IPC. Lastly, the IPC acknowledges
computerized vent design, as long as it is determined by an approved computer program. This computer- ized design can result in dramatically reduced vent sizes as small as ½" and
presumably made of copper for sizes of 1½" or less. All told the IPC seems to be a very
progressive Code with respect to vent sizing. However, on the project I men- tioned at the beginning of this article, one of the first comments we received from the plan reviewer was, and I quote, “Circuit vents and wet vents will not be allowed. Even though the IPC allows it to be installed on Army and Air Force facilities, it will not be allowed on this Naval facility. This facility is to be flexible and expand- able, which a circuit vent and wet vent system does not allow. Design a stan- dard waste and vent system for entire facility.” So, regardless of which Code you use, the vent design can only be as progressive as the Authority Having Jurisdiction. n
The views and opinions expressed in this column are those of the author and do not reflect those of Plumbing Engineer nor its publisher, TMB Publishing.
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