UNFORM CODES QUESTIONS & ANSWERS

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

Does UPC Section 420.0 (2003) 418.0 (2006/2009) 409.4 (2012/2015/2018/2021) apply to bathtubs and roman tubs with no shower?
- No. Section 420.0 (2003) 418.0 (2006/2009) 409.4 (2012/2015/2018/2021)clearly states that only showers and tub-shower combinations fall under this requirement. Section 414.5 was added in 2009, 408.3 (2012/2015/2018/2021) and now requires bathtub and whirlpool tub fillers to limit hot water to 120º F by a device that conforms to ASSE 1070 or CSA B125.3
For makeup air fans where the exhaust hood controls automatically shutoff the power to the makeup air fan on detection of fire under the hood or the building fire alarm panel is in alarm, are additional duct smoke detectors required by the UMC?
- No, this application could be consistent with 2021 Uniform Mechanical Code Section 609.1 exception number (1). As long as this exhaust is controlled by the exhaust hood, no additional smoke detectors are needed. Otherwise any and all independent air-moving systems including a makeup air unit supplying air in excess of 2000 cfm to an enclosed space within a building are required to have an automatic shutoff.
May CPVC piping be used for hot water distribution "outside" the building?
- IAPMO Installation Standard IS 20 very specifically defines CPVC as suitable for "hot and cold, water within buildings." Section 604.1 allows the use of CPVC for "cold water distribution systems outside a building." Nonetheless, each local Authority Having Jurisdiction has the prerogative of allowing CPVC for hot water distribution outside of the building when all concerns have been addressed by an alternative method of installation.
Would it be an acceptable installation to pipe three air-conditioner condensate lines into one main drain line (1 inch pipe)?
- Yes. Section 310.3 (309.3, 2009; 312.3, 2012; 310.3, 2015, 2018) of the UMC clearly states that the waste pipe may be for one unit or a combination of units. A 1 inch pipe could adequately handle the condensate for up to 40 tons of equipment capacity.
In the UPC: 1. Can a Reduced Pressure Principle Backflow Preventer Assembly be used to separate reclaimed water from potable water? 2. Can a Reduced Pressure Principle Backflow Preventer Assembly be used for protection to refill the reclaimed water systems tank in times when the tank is not receiving water from rainfall? 3. Is an air gap the only way to prevent cross connection from occurring when refilling the holding tank for reclaimed water?
- 1. Yes, Section 1613.0(A) (2009), 1603.4 (2012), 1503.4 (2015, 2018) addresses the use of potable water as make-up water for reclaimed water systems. That section states, “…Potable water supplied as makeup water in these systems shall be protected against back-pressure and back-siphonage to accordance with Section 602.0 and 603.0.” Section 602.2 requires the installation of a “backflow prevention device approved for the potential hazard” when connecting potable water systems to piping carrying water that has been used for other uses. 2. Yes (see first answer). 3. No, though an airgap is the optimum type of protection for a high hazard installation such as this, other devices designed for maximum protection of the potable water system may be used. Note: Section 1603.4 (2012) 1503.4 (2015, 2018) requires an airgap or reduced pressure backflow preventer where potable water is used for makeup water for the reclaimed water system.
Under what specific conditions or installations would the requirement not have to be met, to provide 18 inches of clearance between ducts and the ground in a crawl space?
- The code requirement must always be met, although the duct does not necessarily have to maintain 18 inches of clearance for its entire developed length if there is a path maintained to access all areas of the crawlspace. The intent of the code is to make certain that a duct does not block access to areas of the crawlspace. If a person could easily go around a duct to access a portion of the crawlspace, then that portion of the duct would not be required to have 18 inches of clearance as long as it had a minimum of 4 inches of separation from earth. The substantiation for the code change as printed in the 2004 Report on Proposals states “often ducts are installed in crawl spaces and block all access. It is often necessary to cut air ducts apart to gain access to a crawl space area or tunnel under the duct.”
In the case of constructing a new gable roof over an existing flat roof on an apartment complex, are there any circumstances that would allow a plumbing vent to terminate below the new roof? Would the open sides and ends have any affect on waiving the termination requirements?
- No. Any vent that does not terminate vertically 6 inches or more above the roof, as required in Section 906.1, is not acceptable. The open sides or ends in the building as described do not have any effect on waiving termination requirements. Sewer gas is too dangerous and unsanitary to allow in any part of a building or structure.
When determining the rate of breathing zone outdoor air using UMC Table 402.1 should the calculation include cfm/person and cfm/sqft (area)? Do we use the highest number or the total of both?
- Both values are required to derive an answer.
Is there engineering data available which substantiates that the requirements of the Code are adequate for vent stacks up to nine stories in height?
- While basic engineering principles can generally be applied in pressurized water and gas piping design, sanitary plumbing flows involve complex pneumatic and gravity considerations plus construction and the use of intangibles that defy precise engineering classification. Over the years, this has resulted in the development of a substantial amount of specialized plumbing design formula and practice, adequately documented and broad enough for average application. Much of the supporting data consists of research reports, technical discussion, and mathematics unsuited for inclusion in a craft type code. The UPC requirement for a parallel vent stack with yoke relief vents at each fifth floor in buildings ten and more stories in height is more conservative than that of the National Plumbing Code, which varies in requiring yoke relief cross-over vents only at each tenth floor.
Are domestic clothes dryers allowed to terminate vertically through the roof to a “tee top” flashing without a back-draft damper?
- No. Sections 504.3.1 and 504.1 (2003/2006/2009/2012), 504.4 (2015/2018) of the UMC both state that exhaust ducts shall be equipped with back-draft dampers.
What is the required vent size under the sink (not the foot vent)?
- Per Section 909.1 of the 2015 and 2018 UPC, pipe sizing for island drains “shall be as elsewhere in this code”. Sizing requirements for drainage and vent piping may be found in Tables 702.1 and 703.2. A domestic kitchen sink drain has an assigned drainage fixture unit value of two, requiring a minimum 2” waste line and 1-1/2” vent.
  Note: The 2015 Illustrated Training Manual, Figure 909.1B shows a code compliant drawing of an island sink installation.