Shower Compartment Size (IPC 417.4)

IPC 417.4 wants at least 900 sq in of finished interior area AND at least 30 in in least dimension; the exception allows a least dimension down to 25 in only if the area reaches 1,300. So a 28 x 36 stall has 1,008 sq in -- past the 900 -- and FAILS both paths, because 28 is under 30 and 1,008 is under 1,300. Adding length does nothing for the short side, and for a rectangle the 30 in disc test IS the least-dimension test. A 30 x 30 passes exactly; a 25 x 52 passes exactly by the exception. Measured from the FINISHED interior at the threshold, exclusive of valves, showerheads, soap dishes, and grab bars, and it must hold to 70 in above the drain -- so the tile finish and a bench come out of the number and a low soffit can fail a stall that measures fine at the curb.

area = width x depth; least dimension = min(width, depth); base path passes when area >= 900 sq in AND least dimension >= 30 in; the exception path passes when area >= 1,300 sq in AND least dimension >= 25 in; the compartment complies if either path passes. The other side needed at a given least dimension = max(minimum dimension, minimum area / least dimension) on each path.

IPC 417.4 - shower compartments not less than 900 sq in in interior cross-sectional area and not less than 30 in in least dimension, measured from the finished interior dimension at a height equal to the top of the threshold and at a point tangent to its centerline, exclusive of fixture valves, showerheads, soap dishes, and safety grab bars or rails, continued to a height not less than 70 in above the shower drain outlet; with the exception permitting a least dimension of not less than 25 in where the compartment has not less than 1,300 sq in of cross-sectional area.

Both the base rule and the exception are short prescriptive sentences quoted in state adoptions and code-viewer sites. No table is reproduced and all four thresholds are editable inputs.

Estimate. AHJ and licensed professional govern.

Field names used by the API: width_in, depth_in, base_min_area_sqin, base_min_dim_in, exception_min_area_sqin, exception_min_dim_in, area_sqin, least_dim_in, area_deficit_base, area_deficit_exc, exc_other_needed_in

• Base path 900 sq in AND 30 in least dimension - both requiredIPC 417.4
• Exception path 1,300 sq in AND 25 in least dimension - both requiredIPC 417.4 exception
• Disc test for a rectangle the 30 in disc fits exactly when the short side reaches 30 ingeometry
• Measurement finished interior at the threshold, exclusive of valves, heads, dishes, and grab barsIPC 417.4 wording
• Height the dimension must continue to at least 70 in above the drain outletIPC 417.4
• Not checked door and swing, receptor and drain, waterproofing, the 70 in height, accessible stallsstated scope limit