Spot the Violation

PlumbingFixtures & clearancesLevel 32018 UPC

Tiled basement shower

Looking into a newly tiled three-wall shower in a basement bathroom, over a white stone curb. The walls are large off-white tile and the floor is small gray square mosaic with a square center drain. A green laser distance meter sits on the shower floor against the left wall with its red beam on the right wall and its display reading 30.00 in. A second laser meter sits against the back wall with its beam aimed out toward the curb, also reading 30.00 in. A corner shelf with two bottles is in the back left corner, and a pale blue shower curtain hangs gathered at the right side of the opening. 30.00 in 30.00 in
Basement bathroom, custom tiled shower

What's wrong here?

  1. At 30 by 30 in., the shower has only 900 sq in. of floor area; a shower compartment needs at least 1,024 sq in. as well as room for a 30 in. circle
  2. Nothing is wrong because a 30 in. circle fits inside the compartment
  3. A shower without a door must be at least 36 in. wide
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

The finished shower compartment is 30 x 30 in., which is 900 sq in., less than the 1,024 sq in. minimum floor area for a shower.

Correct choice: 1. At 30 by 30 in., the shower has only 900 sq in. of floor area; a shower compartment needs at least 1,024 sq in. as well as room for a 30 in. circle

UPC 408.6 requires every shower compartment, whatever its shape, to have a finished interior of at least 1,024 sq in. and also to be able to contain a 30 in. circle, measured at the height of the top of the threshold. Those are two separate tests: a 30 x 30 in. square holds a 30 in. circle exactly, but its area is only 900 sq in. Even taking the depth to the centerline of the curb, as 408.6 allows, this stall is about 30 x 32-1/4 in., roughly 968 sq in., and still fails. The size has to be held up to 70 in. above the drain, with only valves, heads, soap dishes, shelves and grab bars projecting into it. Measuring finished tile, not framing, is what catches this: a 32 in. framed alcove loses about an inch on each side to backer board, mortar and tile.

How to fix it

Reframe the alcove so the finished interior is at least 32 x 32 in. (1,024 sq in.) or another layout such as 30 x 36 in. or 32 x 48 in. that meets both the area and the 30 in. circle, then rebuild the pan and tile.

Code reference

  • UPC 2018 408.6 — Shower Compartments

    Shower compartments, regardless of shape, must have a finished interior of at least 1,024 sq in. and must also be able to encompass a 30 in. circle. The area and dimensions are measured at a height equal to the top of the threshold and at a point tangent to its centerline, and must be maintained up to at least 70 in. above the shower drain outlet with no projections other than valves, showerheads, soap dishes, shelves and grab bars.

    Drills citing 408.6

Minnesota

MN adopts this rule as writtenConfidence: medium

Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). No Minnesota amendment to UPC 408.6 is known; check ch. 4714 before relying on it. Search excerpts suggest Minn. Rules 4714.0408 amends other parts of UPC 408 (reportedly the shower liner rules in 408.7), not the compartment size; that was not confirmed against the rule text.

About the Minnesota Plumbing Code

Why the other choices are wrong

  • Nothing is wrong because a 30 in. circle fits inside the compartment. The 30 in. circle is only half of UPC 408.6; the compartment must also have at least 1,024 sq in. of finished interior, and 30 x 30 in. is only 900.
  • A shower without a door must be at least 36 in. wide. The UPC has no door-based width rule; a curtain is fine, and the size test is the same 1,024 sq in. and 30 in. circle with or without a door.
  • Nothing. This installation is compliant. The finished interior is 30 x 30 in., which is 900 sq in., under the 1,024 sq in. minimum in UPC 408.6.
Code complianceLevel 3 · Master#shower#shower size#1024 square inches#tile#basement#measurement

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