May 14, 2026
From the 2024 UPC Illustrated Training Manual, Chapter 10, TRAPS AND INTERCEPTORS
1002.4 Vent Pipe Opening. The vent pipe opening from soil or waste pipe, except for water closets and similar fixtures, shall not be below the weir of the trap.
This requirement is similar to Section 905.5 and has been discussed in Section 1002.2. Caution is needed in using the proper fitting in connecting the trap arm to the waste and vent connection. In the vertical position the sanitary tee will be the proper fitting for most installations. The use of a combination wye and one-eighth bend will not be allowed as it places the inner edge of the vent below the weir of the trap. See Figure 1002.4 for an improper use of a double wye and the improper length of clothes washer standpipes.
IMPROPER FITTINGS USED FOR VENT CONNECTION
From the 2024 UMC Illustrated Training Manual, Chapter 6, DUCT SYSTEMS
608.2 Dwelling Units. The use of under-floor space shall be limited to dwelling units not more than two stories in height. Except for the floor immediately above the underfloor plenum, supply ducts shall be provided extending from the plenum to registers on other floor levels.
Exception: In flood hazard areas, under-floor spaces shall not be used as supply plenums unless the flood opening requirements in the building code are met.
This section regulates the use of under-floor space as an HVAC supply plenum in single-family residences. The requirements for supplying heated air to under-floor space limits air temperature that comes into contact with exposed wood construction, and at the same time limits the volume of underfloor air to be heated each time the circulating fan is turned on. Figure 608.2 illustrates the requirements of this section.
UNDER-FLOOR SPACE AS SUPPLY PLENUM
(This is not to be considered the official position of IAPMO, nor is it an official interpretation of the Codes.)
IAPMO
IAPMO develops and publishes the Uniform Plumbing Code®,the most widely recognized code of practice used by the plumbing industry worldwide; Uniform Mechanical Code®; Uniform Swimming Pool, Spa and Hot Tub Code®; and Uniform Solar Energy, Hydronics and Geothermal Code™ — the only plumbing, mechanical, solar energy and swimming pool codes designated by ANSI as American National Standards — and the Water Efficiency Standard (WE-Stand)™. IAPMO works with government, contractors, labor force, and manufacturers to produce product standards, technical manuals, personnel certification/educational programs and additional resources in order to meet the ever-evolving demands of the industry in protecting public health and safety.
Last modified: May 9, 2026