§ 215. Alcoves. No part of any room shall be enclosed or subdivided, wholly or in part, by a curtain, portiere, fixed or movable partition or other contrivance or device unless each such enclosure or subdivision shall contain a separate window conforming to the provisions of section thirty for rooms in multiple dwellings erected after April eighteenth, nineteen hundred twenty-nine, and have a clear floor area of at least seventy square feet.