Bathtub trap in a crawlspace
What's wrong here?
- Nothing. This installation is compliant
- The trap arm is too long for a 1-1/2 in. trap
- A fixture trap may not hang below the floor in a crawlspace
- The vent cannot be taken off a sanitary tee; a wye is required
Show the answer and the code reference
The answer
Nothing is wrong: the 1-1/2 in. tub trap arm is about 30 in. long, the vent rises from the top of a sanitary tee above the trap weir, and the drain below has a cleanout.
Correct choice: 1. Nothing. This installation is compliant
UPC 1002.2 requires the developed length of a trap arm, from the trap weir to the vent fitting, to be within Table 1002.2: 3 ft 6 in. for 1-1/2 in. This arm is about 30 in. UPC 905.5 keeps the vent opening from being below the trap weir, and taking the vent straight up out of the top of an upright sanitary tee does that. A trap below the floor is fine as long as its slip joint is accessible, which it is from the crawlspace, and the cleanout tee at the base of the drop gives a way to rod the drain. The arm is strapped, and the 2 in. drain below is pitched toward the building drain.
How to fix it
No correction needed. On an inspection, measure the trap arm from the weir to the inner edge of the vent and check that it is graded at about 1/4 in. per foot, the slope Table 1002.2 is based on.
Code references
UPC 2018 1002.2 — Fixture Traps
Each fixture trap shall have a protecting vent located so that the slope and the developed length of the fixture drain from the trap weir to the vent fitting are within Table 1002.2 (1-1/2 in. trap arm: 3 ft 6 in., based on a 1/4 in. per ft slope).
Drills citing 1002.2UPC 2018 905.5 — Location of Opening
The vent pipe opening from a soil or waste pipe, except for water closets and similar fixtures, shall not be below the weir of the trap.
Drills citing 905.5
Minnesota
Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). Search-result excerpts indicate Minnesota amends UPC 1002.2 (apparently in part 4714.1002) while keeping the Table 1002.2 trap arm distances (3 ft 6 in. for 1-1/2 in.), but the amended text could not be read; check ch. 4714 before relying on the details. This installation is compliant under the model code and under the reported Minnesota wording.
About the Minnesota Plumbing CodeCitation under review. Minnesota status is unverified: confirm what Minn. Rules ch. 4714 (apparently part 4714.1002) changes in UPC 1002.2 and Table 1002.2. Also confirm the 2018 UPC headings and numbering for 1002.2 ('Fixture Traps') and 905.5 ('Location of Opening', vent opening not below the trap weir). The compliant verdict holds as long as the 3 ft 6 in. limit for a 1-1/2 in. trap arm stands.
Why the other choices are wrong
- The trap arm is too long for a 1-1/2 in. trap. The arm runs about 30 in. from the trap weir to the tee (under two joists at 16 in. on center); Table 1002.2 allows 3 ft 6 in. for 1-1/2 in.
- A fixture trap may not hang below the floor in a crawlspace. Tub and shower traps are routinely set below the floor. What matters is that the trap is vented within the Table 1002.2 distance and that any slip joint stays accessible, which it is from the crawlspace.
- The vent cannot be taken off a sanitary tee; a wye is required. A sanitary tee is the normal fitting where a horizontal trap arm meets a vertical waste-and-vent pipe, and its top outlet puts the vent opening above the trap weir as UPC 905.5 requires. Wyes are for horizontal-to-horizontal and vertical-to-horizontal changes.