D.C. Mun. Regs. tit. 14, r. 14-507
Each bathroom shall be naturally or mechanically ventilated, at least equivalent to the requirements of this section.
Natural ventilation shall be provided by openings, other than a door, directly to the outside, the openable area of which is at least equal to five percent (5%) of the floor area of the room served.
No opening for ventilation of a bathroom shall contain less than two square feet (2 ft.2).
If mechanical ventilation is used, it shall provide for each bathroom with a single water closet outside air in a minimum quantity of one and one half cubic feet per minute per square foot of floor area (11/2 ft.3/min./ft.2), with no recirculation permitted.
A bathroom having more than one water closet shall be provided with a minimum outside air quantity of two and one half cubic feet per minute per square foot of floor area (21/2 ft.3/min./ft.2), with no recirculation permitted.
A mechanically ventilated bathroom shall not serve or open into any area that opens on, or is served by, a bathroom that is not similarly ventilated.
D.C. Mun. Regs. tit. 14, r. 14-507