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Uniform Codes Questions & Answers 

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

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.

1. Is 5/8 inch Type X gypsum wallboard considered a combustible per the UMC in reference to clearances from single-wall gas vents? 2. Would it be acceptable per the UMC to reduce the clearances between a single-wall gas vent and 5/8 inch Type X gypsum wallboard by applying paint to the wallboard?

1. Yes. Gypsum wallboard does not meet the definition of noncombustible as defined in Section 216.0. 2. No. Acceptable methods of clearance reduction can be found in Table 3-2 as per footnote 2 of Table 3-3 (Table 3-3 as per footnote 2 of Table 3-4, 2009).Other methods of clearance reduction would be considered an alternate method.

Does UPC Section 905.3 require the use of a combination wye and 1/8 bend installed on its back as a vent connection to a horizontal drain at which point the vent is below the flood level rim of the fixture being served?

The correct fitting to be used for this type of installation is a combination wye and 1/8 bend. Section 905.3 states that vents less than 6 inches above the flood level rim of the fixture shall be installed with approved drainage fittings and material. A sanitary tee installed in a horizontal position is not an approved drainage fitting.

1. Is an attached garage (unheated and uninsulated space with ventilation from the outside) considered a "cold area"? If so, then would a Type B or Type L vent connector be required? 2. Does the definition of "cold area" include a garage?

1. Yes, the garage is considered a cold area. The UMC requires a Type B or L vent or other equivalent means of insulation. 2. A "cold area" is defined as having or being a temperature that is uncomfortably low for humans and not heated. In summary, the object is to prevent condensation. The interpretation of a "cold area" will depend on climate and the opinion of the Authority Having Jurisdiction.

1. Are the men's and women's bathrooms in a retail store that are open to the public use required to have metered faucets on lavatories? 2. In state or office buildings where there are central bathrooms (men's and women's) which are intended to serve the transient public, are metered faucets on lavatories required? 3. What does transient mean?

UPC Section 402.4 (2003/2006/2009) 403.4 (2012) 407.2 (2015) references "transient public". In this instance the purpose is to distinguish between one element of the public occupancy and another element. Webster's Ninth Collegiate Dictionary defines transient as "temporary; fleeting; passing quickly. Metered faucets are required as the concern addressed by the code is the potential for misuse by the transient public which has no vested interest in appropriate utilization of public buildings or their facilities As opposed to employees who require extended and predictable periods of occupancy.

1. Do the requirements for UMC Section 510.7.2 apply to a building more than one story and one story building where roof ceiling assembly is required to have fire-resistance rating? 2. If yes, is it the intent of the code that other single story buildings that are not a part of Section 510.7.1 shall be governed by Section 510.7.2.1? 3. Would Section 510.7.2.3 still apply if Section 510.7.2.1 is met? (i.e. building is single story and has a enclosure of 1 hour or more and is not a building as defined in Section 510.7.1 or Section 510.7.1.1)

1. Yes. Section 501.7.2 only applies to buildings more than one-story in height and in one–story buildings where the roof-ceiling assembly is required to have a fire resistance rating as addressed in Section 510.7.1. 2. No. Section 510.7.2.1 only applies to buildings defined in Section 510.7.1. 3. Section 510.7.2.3 applies to both Sections 510.7.2.1 and 510.7.2.2. All of Section 510.7.2 applies to Section 510.7.1. If you are referring to a single-story non-rated building where an enclosure is not required, all clearances shall meet the requirements as stated in Section 507.2.1.

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