Much is new regarding engineered design concepts. Not so with nonwater-supplied urinals and air admittance valves.

This year, each of the model plumbing codes published a new edition: the 2009 edition. For the IAPMO Uniform Plumbing Code (UPC), this is a year in which the new code brings about changes. At the same time, it is an off year, whereby there are no code changes to be considered.

The next code change cycle for the UPC begins next February, and Feb. 2010 is the deadline for submitting any changes to the 2012 code. IAPMO has code change forms available on its Web site,

The hot subjects that have haunted the UPC for the past few years have been: non-water-supplied urinals, engineered design and air admittance valves. The first two appear in the 2009 edition.

After much debate, nonwater-supplied urinals were added as an acceptable fixture. Included with the approval is a requirement that a water supply be roughed in the wall behind the urinal to allow a retrofit. The code is not clear as to the exact location of this water line. It will be subject to the interpretation of the local inspector.

One could conclude that the water line merely be located somewhere in the wall. Others may consider a requirement for the water line to be where a flush valve would be located. However, the question would become, “What urinal would replace the nonwater-supplied urinal, and what flush valve?” Depending on the products, the water line could be in different locations.

Major Changes to Engineered Design

With regard to engineered design, major changes appear in the 2009 edition. In Chapter 9, there is an added reference to allow an engineered vent system. The key requirement for an engineered vent system is that the design and installation protect the trap seal.

A new section was added, stating that a trap seal must not be exposed to pressure differentials that exceed one inch of a water column. It is somewhat surprising that this was never stated in the UPC. However, it has always been the understanding of the design of a venting system.

Appendix L has a number of engineered design concepts for venting. Many of these concepts already appeared in the 2006 edition. One of the reasons for adding the engineered vent system section was to clarify, to the authority having jurisdiction, that such an engineered design is permitted in the body of the code. Some inspectors were interpreting Appendix L as not being a part of the code. However, Chapter 3 already allows an engineered design and, hence, Appendix L is applicable.

Chapter 7 on sanitary drainage had always permitted an engineered design for the drainage system. A change to Appendix L adds new sizing requirements for an engineered drainage system. The new requirements are consistent with Hunter design parameters. The UPC was the last remaining code that did not completely embrace all of Hunter’s principles. With the change to Appendix L, that is no longer the case.

The sizing and design method in Appendix L is consistent with theASPE Plumbing Engineering Design Handbooksizing methods. The tables were extracted from ASPE, with ASPE’s permission. As a result of these changes, some of the pipe sizing in high-rise construction will be reduced in size. Along with the reduction in size is a requirement for venting any drainage offset. Prior to this edition, the UPC addressed the pressure differentials in an offset by upsizing the piping. With a reduction in sizing, venting becomes necessary. For buildings, less than six stories in height, an offset vent is not required.

Included with the new drainage piping sizing method in Appendix L is a new engineered vent sizing method. This will also result in smaller size vents for many installations, especially taller buildings.

I would advise every plumbing engineer to check out the allowable design and sizing methods found in Appendix L.It should also be noted that IAPMO has issued an interpretation stating that you must be a licensed professional engineer to use Appendix L. This interpretation is completely appropriate since it is an engineered design appendix.

Another change that will impact the plumbing engineered design is to the horizontal wet venting section. One of the changes is merely a clarification. It states that fixtures must connect horizontally to the wet vent system or have a dry vent connection. Of course, that is the concept of wet venting.

The change that will impact certain designs is the statement that the water closet shall be the most downstream fixture in a wet vent system. This was the basis for Hunter’s study in the early part of the last century. Of course, later research indicated that the placement of the water closet had no impact on the performance of the wet vent. It should be noted that many plumbing engineers already design wet vent systems with the water closets being the most downstream fixture.

AAVs Left Out

The last of the three hot issues, air admittance valves, did not make it into the 2009 edition of the UPC. The IAPMO Plumbing Technical Committee had approved air admittance valves as a part of Appendix L. However, the membership removed this section. The interesting fact is that Appendix L still allows air admittance valves to be used as a part of an engineered vent design. This is also permitted by the engineered vent section in Chapter 9.

The only thing the membership accomplished with the change to Appendix L was to remove a valuable reference that the authority having jurisdiction could use. Now, when evaluating an engineered design utilizing air admittance valves, there are no guidelines in the UPC. Basically, the inspector is at the mercy of the plumbing engineer. However, that is not all that bad since a plumbing engineer should be very well-versed in the design of a vent system using air admittance valves.

While air admittance valves do not appear in the code, Studor has filed an appeal to ANSI requesting that air admittance valves be added. Studor appealed both the ASPE change to add requirements to Appendix L and its own change to add requirements to Chapter 9. There is validity to the appeal regarding the ASPE change to Appendix L. Although, that doesn’t mean that Studor will win its appeal.

Finally, there is a new design and sizing method for grease interceptors. The new sizing methods are consistent with the recommendations of the Plumbing and Drainage Institute.