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Uniform Codes Questions & Answers 

Every week we will be including additional questions and informal UPC and UMC interpretations

1. Where can listed air duct connectors be used in compliance with the UMC? 2. Would an electric water heater be allowed to be installed in a return air plenum?

1. Listed or not, air duct connectors are only approved for use with domestic clothes dryers (reference Section 504.3.2.1, Exception).They may be installed between the domestic clothes dryer and the moisture exhaust duct. 2. Yes, but the electric water heater and wiring must be listed for plenum use.

This question regards the use of a combination waste and vent system installed in a public school (Section 910.0 and Appendix B). This system receives the waste from kitchen sinks which are equipped with waste disposal units. These sinks are located in a home economics classroom. Would this system be acceptable if the disposals were eliminated? I do not believe this type of system is acceptable for receiving the discharge from kitchen sinks or other apparatuses which discharge grease or excessive soap residue.

UPC Section 910.0 permits a combination waste and vent system only if structural conditions preclude the installation of conventional plumbing. Appendix B specifically requires that sinks, lavatories and other fixtures which rough-in above the floor not be permitted to discharge into a combination waste and vent systems. Combination waste and vent systems are intended primarily for extensive floor drain and shower installations where separate venting is not practical, and for floor sinks in markets, demonstration or work tables in school buildings, or similar applications where the fixtures are not adjacent to walls or partitions. Due to the oversized characteristics of this type waste system (which is not self-scouring), grease producing fixtures such as sinks, lavatories, etc., should not be connected to a combination waste and vent system. Discharge of other than clear water waste into an indirect waste receptor would not comply with the intent or provisions of Appendix B, Section 910.0, or Section 304.0.

I am looking for clarification for the use of a plastic start collar (duct fitting) in the UMC. Is a fitting that passes the UL 2043 test standard (produces smoke having an average optical density not greater than 0.15 and having a peak optical density of 0.5 or less when tested in accordance with UMC Standard No. 6-3.) allowed to be used in commercial construction under the UMC? These types of fittings are not mentioned in the UMC.

No. Materials exposed within ducts must be tested in accordance with NFPA 255, ASTM E84, or UL 723, except as indicated in the exceptions. Exception 8 of Section 602.2 which addresses UL 2043 provides approval for loudspeakers and recessed lighting fixtures, including their assemblies and accessories. Exception 8 would not apply to plastic start collars.

When joining 304 stainless steel to copper piping do you need to install a dielectric union or coupling to separate the metals?

The UPC allows the use of stainless steel pipe and Section 605.17.3 (2012), 605.16.3 (2015)Stainless Steel to Other Materials states: Where connecting stainless steel pipe, mechanical joint of the compression type, dielectric fittings, or dielectric union in accordance with ASSE 1079 and designed for the specific transition intended shall be used.

On a facility or project that is seismically engineered with detailed drawings showing bracing and guying, prepared by seismic consultants, is additional bracing still required on ducts smaller than six square feet of cross-sectional area for a rectangular duct or a 28 inch diameter or smaller round ducts?

The code requires that ducts be braced and guyed to prevent lateral or horizontal swing. It does not limit the size of the duct and does not say specifically how it is to be achieved. If the Administrative Authority accepts and approves an engineered design, the installation should be installed per the approved design.

Is a backflow preventer required where a reverse osmosis system is installed?

Potable water must always be protected from backflow, which could degrade its potability. If the process of treating the potable water represents a threat to its potability, then all such "treated" water must be isolated by appropriate backflow protection. If neither the treatment nor the application of the water results in degradation of its potability, then no special backflow protection is necessary.

1. Is the method proposed by ASHRAE Fundamentals 2007 Chapter 13 (Page 13.18) be acceptable alternate method to UMC Table 4-4, for parking garage exhaust? Justification: UMC Chapter 4 exhaust rate refers to ASHRAE 62.1. ASHRAE Fundamentals Chapter 13 explains that due to reductions in vehicular CO emissions, exhaust rates should be generally going down, and that the method proposed in Chapter 13, is based on further study projects conducted by ASHRAE. 2. Can the exhaust rate be verified based on CO monitoring in the garage? The current code does not address this in relation to UMC Table 4-4. However, UMC Section 403.6 (2006/2009) does allow dynamic reset of ventilation airflow. We would like to know if a CO monitoring method can be allowed for dynamic reset of exhaust airflow rates. With more and more owners having interest in LEED projects, a consideration to be able to dynamically vary the exhaust rates would likely save a lot of fan energy, particularly in the non-peak hours.

1. Yes, if the Authority Having Jurisdiction determines the proposed design is equivalent to the requirement of the code. In addition, the system would need to be designed as a product-conveying ventilation system per Section 505.0 of the 2006/2009/2012 UMC. 2. No, not per Section 505.2 (2003/2006/2009/2012) of the code, although the AHJ may approve a design that incorporates a variable system if it is determined to be equivalent to the code.

Does the piping upstream of the water closet need to be 3" even though the fixture unit DFU is 4 or less?

UPC Section 908.4.3 (2006), 908.2.1.2 (2009), 908.2.2 (2012/2015) UPC allows four (4) DFU units on a 2 inch horizontal wet vent. The total DFU values affixed to a bathtub and lavatory is 3 DFU per Table 7-3 (2006/2009), Table 702.1 (2012/2015). A 2” wet vent would be permissible by Code.

If a packaged rooftop air conditioning unit is serving several small offices, can the total volume of all spaces served be included in the calculation of permissible refrigerant quantities?

Yes, as long as the dampers have a permanent stop allowing not less than one quarter of the area to be closed off.

Would a hose bibb in a restroom constitute adequate trap seal protection as required by UPC Section 1007.0?

No, since trap seals are essential to protect the building from sewer gas, Section 1007.0 requires that traps subject to “infrequent use” must be provided with an approved automatic means of maintaining their water seals.

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