R303.3 Bathrooms. Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m 2), one-half of which shall be openable. Exception: The glazed areas shall not be required where artificial light and a local exhaust system are provided.
Shower compartments shall have not less than 900 square inches of interior cross-sectional area. Shower compartments shall be not less than 30 inches in minimum dimension measured from the finished interior dimension of the shower compartment, exclusive of fixture valves, shower heads, soap dishes, and safety grab bars or rails. The National Kitchen & Bath Association developed Bathroom Planning Guidelines with Access Standards to provide designers with good planning practices that consider the needs of a range of users.
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In other than dwelling units, toilet, bathing and shower room floor finish materials shall have a smooth, hard, nonabsorbent surface. The intersections of such floors with walls shall have a smooth, hard, nonabsorbent vertical base that extends upward onto the walls not less than 4 inches (102 mm). The ceiling height above bathroom fixtures must enough for the fixture to be used for its intended purpose [IRC R305.1 (2)].
A shower or tub equipped with a showerhead shall have a minimum ceiling height of 6-feet 8-inches above an area that is 30-inches square [IRC R305.1 (2)]. There is some additional clarity provided in this exception, however. Where a showerhead is provided over a bathtub or shower pan (called "fixtures" in the IRC), there must be at least 6 ft.
Residential Bathroom Code Requirements Bc at Vernon Minjares blog
8 in. of ceiling height at the showerhead for a horizontal area of not less than 30 in. by 30 in.
1. rooms with sloped ceilings, at least 50% of the required floor area must have a ceiling height of at least 7' and none less than 5' 2. bathrooms shall have a minimum ceiling height of 6'8".
STANDARDS.pptx
The area of a bathroom shall not be less than 1.8 m2 with a minimum width of 1.2 m. The floor area of water. The ceiling height above bathroom and toilet room fixtures shall be such that the fixture is capable of being used for its intended purpose.
A shower or tub equipped with a showerhead shall have a ceiling height of not less than 6 feet 8 inches above an area of not less than 30 inches by 30 inches at the showerhead. 2016 NFPA 13R says sprinklers SHALL not be required in bathrooms where the bathroom area does not exceed 55-sq. ft.
So the inverse would also be true: Sprinklers SHALL be required in bathrooms where the bathroom area exceeds 55-sq. ft. In your case, the bathroom does in fact exceed 55 sq.
ft. So you'll need to protect this bathroom unless they make it smaller.
