UNFORM CODES QUESTIONS & ANSWERS

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

Can PVDF be installed in a non-combustible plenum?
- Yes, when it meets the requirement of Section 602.2 of the UMC and is installed in compliance with its listing and installation instructions.
Can two traps be installed on one branch without reventing on a combination waste and vent system?
- Yes, provided that the branch serving more than one trap on a combination waste and vent systems does not exceed 15 feet in length and has a cleanout installed at its upper terminal, as required by Section 910.6. See also Appendix B
1. Does the code allow a Type I hood to be exposed to the attic space provided it meets all the clearance requirements in Section 507.2? 2. In other words, can a T-bar ceiling terminate at the hood flashing and not continue over the hood provided all the required clearances are maintained? 3. Is a Type I hood allowed to penetrate a non fire-rated ceiling without an enclosure?
- 1. Yes, but only in a one-story building where the roof-ceiling assembly is not required to have a fire-resistance rating or where the hood penetrates a non fire-rated ceiling in a building more than one-story. The code states, “In 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, the ducts shall be enclosed in a continuous enclosure extending from the lowest fire-rated ceiling or floor above the hood.” 2. Yes, as long as it meets the requirements of #1 and the ceiling is listed as a noncombustible. 3. Yes, as long as it meets the requirements of #1, except that if there are additional stories above the hood, an enclosure would be required commencing at the point where the grease duct penetrates the floor above.
Does the UPC permit a sink and lavatory to discharge into the 3 inch vent stack above a water closet and shower in a single family dwelling without reventing the water closet and shower?
- There are two separate answers to the question as stated. 1. Yes, the lavatory may wet vent the water closet, provided the wet vented section is one pipe size larger than the minimum required waste pipe size for the upper fixture(s). 2. The shower may be wet vented in a similar manner.
Conditions: 1 story building with exterior concrete walls and a wood roof, not sprinklered with a t-bar ceiling at 10'-0", can we have a non-ducted return air system if we have plenum rated cables and wires?
- No, this requirement is not limited to exposed plenum cables and wiring. Section 602.2 of the 2021 Uniform Mechanical Code begins by stating that “materials exposed within ducts or plenums shall be noncombustible or shall have a flame spread index not to exceed 25 and a smoke developed index not to exceed 50.” This requirement would include all exposed construction materials. The wood roof is considered combustible and would not meet the 25/50 flame and smoke index requirements.
In the UPC: 1. Is there a limit on the number of unvented, untrapped fixtures allowed on a sand interceptor? 2. Is there a maximum distance from the floor drains to the sand trap? 3. Does standard waste sizing per Chapter 7 apply to such a system?
- 1. There is no fixture limit imposed by code. In reality, an untrapped, unvented drainage piping system is similar in character and function to an open trough drainage system. An untrapped/unvented pipe system is effectively a closed trough. 2. Again, there is no limit imposed by code. There is obviously a practical limitation resulting from interceptor burial depth and the need for adequate pipe flow to prevent settling of sand and other materials in the pipe due to flow velocities. 3. Standard waste pipe sizing would apply. Oversizing should be avoided. As noted earlier, it is important that slope, water volume, and pipe area be selected which will assure the greatest degree of scouring action. Piping which is too flat, or which is oversized, will fail to carry materials such as sand all the way to the interceptor, thereby creating drainage problems rather than curing them. In summary, certain waste products must be intercepted or treated prior to entering the sanitary waste system. A conventional trap and vent system is unsuitable for sand-bearing waste because "self-cleaning" (Section 1003.1) of a trap is limited by the density of the waste products passing through it. Therefore, a trough (open or closed) is the best means of assuring that such products will reach the intended interceptor. Note: All interceptors are required to be vented, whether they have gastight covers or not (Section 1009.4,2003/2006/2009/2012/2015; Section 1009.5 2018/2021). The interceptor vent will be located within standard trap arm length based upon the nominal trap arm diameter.
Is there any language in the mechanical code that would restrict or prohibit supplying combustion air from a ventilated attached garage ceiling to a remote mechanical room elsewhere in the house?
- You cannot bring combustion air from a garage. Combustion air shall not be obtained from a hazardous location or from any area in which objectionable quantities of flammable vapor are released. Combustion Air ducts would be limited to approved materials for their intended use.
When are “existing, non-compliant” materials, equipment, or plumbing systems required to be replaced with currently compliant products or installation requirements?
- Existing systems may remain in service when maintained in accordance with the law in effect prior to the effective date of this Code, provided that no hazard to life, health, or property exists, or would be created by such ongoing utilization.
My city has a number of buildings which are being converted from LPG to natural gas as fuel for water heaters, furnaces, and ranges. Some of these conversions consist of only new gas piping being installed outside the structure from the meter location to the supplier’s gas main. Is it the intention of the UMC to require a pressure test on the entire system when no modification to the existing building piping has occurred? All new gas piping outside the building will be tested.
- No. The Authority Having Jurisdiction may use discretionary authority to waive the test on the existing portion of a gas piping system, provided that it has been determined that the existing work has not suffered structural damage, complies with the sizing and material requirements of the code, and was previously properly tested.
Where in the UPC is the specific code that prohibits untreated rainwater from being introduced into a building?
- The UPC allows non-potable water to be used in some applications. Chapter 17 (2012), Chapter 16 (2015) regulates non-potable rainwater catchment systems. The installation of rainwater catchments systems is only intended to supply uses such as water closets, urinals, trap primers for floor drains and floor sinks, irrigation, industrial processes, water features, cooling tower makeup and other uses shall be approved by the Authority Having Jurisdiction.
  Appendix K if adopted would allow the rainwater to be treated to potable standards and be used for drinking purposes.