Designer’s Guide Venting: IPC vs. UPC
Timothy Allinson, P.E., Murray Co., Long Beach, Calif. A
s you may have noticed, I usually write about design in the context of the UPC, the Code that governs the work I do here in California. Well,
ironically enough, I am doing a project for the Navy, which is governed by the IPC, even though it is California based, because the IPC governs all Navy projects nation- wide. This project necessitated that I get up to speed with the latest IPC, and the biggest difference I discovered between the two Codes is that of venting. For the sake of this article, it is worth noting that I am comparing the 2009 IPC with the UPC of that same year. In the IPC, vent stacks are required for every waste
stack of five branch intervals or more. In the UPC, this requirement doesn’t kick in until branch intervals reach 10 stories or more. Vent stacks must be connected to the base of the waste stack in both Codes. In the UPC, waste and vent stacks must be interconnected with a yoke vent every five floors, while the IPC requires relief vents every ten stories. The IPC also requires a relief vent for stack offset where there are five stories or more above the offset. This relief vent must be connected to both the upper and lower
sections of the vent offset. Horizontal vent terminations are allowed by the IPC,
through exterior walls that are 10 feet from the lot line and at least 10 feet above grade and screened from birds, varmints, etc. This is a handy allowance that the UPC does not provide. Oddly, the IPC requires that vents in freezing climates (0-degree design temp) be insulated above the roof. In contrast, the UPC requires that they be at least 2" in size or larger to satisfy design conditions. Each of these requirements is meant to prevent frost closure from freez- ing vapor emitted by the vents. Trap arm distances— downstream side of trap to vent
— also vary between Codes, the IPC being more lenient, double in fact. The UPC allows 4', 6' and 8' trap arms for 2", 3" and 4" trap arms, respectively. The IPC allows 8', 12' and 16' for these same trap arm diameters. Common vents in the UPC are allowed for fixtures at
the same elevation, such as back-to-back lavatories. In the IPC, common vents tread into the territory of wet vents as Continued on page 16
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Circle 9 on Reader Reply Form on page 38 Page 14/Plumbing Engineer February 2011
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