Drain traps must be prevented from losing their water seals. Loss of the water seal allows sewer gas to enter the building.
The International Plumbing Code (IPC) Section 1002.3, 2018 edition, discusses the types of prohibited traps. Specifically, the first type of trap that is prohibited is “Traps that depend on moving parts to maintain the seal.” Some interpret this language to prohibit the use of trap seals.
The Code Commentary states that “a trap is intended to be a simple U-shaped piping arrangement that offers minimal resistance to flow. Prohibited traps do not have a simple U-shaped design or configuration.” A P-trap with a trap seal still has the simple U-shaped design or configuration. Regarding this first prohibition, the Code Commentary states, “Item 1 refers to mechanical traps that use moving parts such as floats or flappers.”
Note that this code language is in reference to traps, not trap seals.
Although the Code Commentary is not mandatory code language, it provides insight into the code committee’s intent. Section 1002.3.1 prohibits the use of mechanical traps, not U-shaped piping, with the addition of a trap seal.
Also, to interpret 1002.3.1 as prohibiting trap seals is a direct contradiction of 1002.4.1.4, which permits barrier-type trap seal protection devices conforming to ASSE 1072 as a method for trap seal protection. Section 1002.4.1 Trap Seal Protection provides four acceptable methods for trap seal protection. Trap seal devices are one of them, as noted in 1002.4.1.4.
To correctly interpret the IPC, the distinction between traps and trap seal protection must be recognized. Traps are covered in 1002.3 and trap seal protection is covered in 1002..4.1, respectively.
Ultimately, the decision on whether to use trap primers or trap seal devices for trap seal protection is the judgment of the design engineer; however, I do not believe the IPC, specifically Section 1002.3.1, prohibits the use of trap seals.
