Plumbing Fixture Clearances (IPC 405.3.1)
The bathroom rough-in check, in four numbers: 15 in from a fixture centerline to any side wall, partition, vanity, or other obstruction; 30 in center to center between adjacent fixtures with no partition between them; 21 in of clearance in FRONT to any wall, fixture, or DOOR; and a floor-mounted water-closet compartment not less than 30 x 60 in. The number that decides a layout before anything is drawn is the derived one: a row of n fixtures needs 2 x 15 + (n-1) x 30 of wall-to-wall width, so two want 60 in and three want 90 -- a 5 ft wall holds two and not three, which is where half-bath layouts come apart. Measure from the CENTERLINE, and remember a door swinging into the 21 in is an obstruction just as a wall is. These are the plumbing FLOOR, not an accessible layout -- ANSI A117.1 and ADA want substantially more. Minimums are editable for local amendments.
Formula and source
pass requires centerline-to-obstruction >= 15 in on each side, adjacent fixture centers >= 30 in apart where no partition separates them, clearance in front >= 21 in, and a floor-mounted water-closet compartment >= 30 in wide by >= 60 in deep. Minimum wall-to-wall width for a row of n fixtures = 2 x 15 + (n - 1) x 30.
IPC 405.3.1, Clearance of plumbing fixtures - a water closet, urinal, lavatory, or bidet not set closer than 15 in from its center to any side wall, partition, vanity, or other obstruction; adjacent fixtures not closer than 30 in center to center where partitions or other obstructions do not separate them; not less than 21 in of clearance in front to any wall, fixture, or door; water-closet compartments not less than 30 in wide and 60 in deep for floor-mounted closets.
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