Each habitable room shall have either natural or mechanical ventilation at least equal to the requirements of this section.
Natural ventilation shall be provided by an opening directly to the outside, the area of which is at least equal to five percent (5%) of the floor area of the room served, except as otherwise provided in this section.
Rooms opening on enclosed porches and meeting the ventilation requirements of Article 501-01-e of the 1941 Building Code, as amended, and rooms ventilated through sunporches and meeting the ventilation requirements of § 3 -515 of the 1961 Building Code, as amended, shall be deemed to have adequate natural ventilation.
At least fifty percent (50%) of the required ventilation shall be furnished by an openable window, louvres located in the upper fifty percent (50%) of the room, side light, transom, glazed door, or door of the horizontally divided (dutch) or vertically divided (french) type.
For buildings erected, altered, or converted under permits issued prior to July 1, 1961, mechanical ventilation where used shall provide habitable rooms, other than kitchens, with at least three (3) air changes per hour.
Kitchens shall be provided with at least four (4) air changes per hour.
Openable area directly to the outside at least equal to three percent (3%) of the floor area of the habitable space served shall be available for use in case of temporary failure of mechanical ventilation, except as provided in § 506.8.
Interior kitchens which are not daylighted as required by § 502 may be artificially lighted and mechanically ventilated if they comply with the following:
Not more than seventy-five percent (75%) of the air supplied by mechanical ventilation shall be recirculated air.
The recirculation of air from kitchens, bathrooms, furnace rooms, laundry rooms, and garages is prohibited.
No air supplied to habitable rooms shall be drawn from a plenum or system fed with air returned from habitable rooms occupied by other families, common space, or commercial or industrial establishments.
For buildings erected, altered, or converted under permits issued after June 30, 1961, the requirements for mechanical ventilation shall be in accordance with the applicable provisions of sections 3 -527 through 3-533, inclusive, of the 1961 D.C. Building Code, as amended.
D.C. Mun. Regs. tit. 14, r. 14-506