§ 217. Lighting and ventilation of public halls and stairs. 1. In every tenement erected after April twelfth, nineteen hundred one, which exceeds four stories in height or is occupied by three families or more on any story, every public hall shall have at least one window opening directly upon a street, yard or court. Such window shall be located at the end of the hall and at right angles to its length, with an additional window in each thirty feet of hall or fraction thereof beyond the first sixty feet from such end window if the tenement was erected after April eighteenth, nineteen hundred twelve; or, if the window is not thus located at the end of the hall, there shall be at least one window opening directly upon a street, yard or court in every twenty feet of the length of the hall or fraction thereof, measured from one end of hall; but the foregoing provisions shall not apply to that portion of an entrance hall between the entrance and the first flight of stairs if the entrance door contains five square feet or more of glazed surface.

2. When the length of any recess or return off of a public hall in such a tenement does not exceed twice its width, no window shall be required therein. But wherever the length of a recess or return exceeds twice its width there shall be an additional window or windows meeting the requirements for a separate public hall.

3. Except as provided in subdivision four, a tenement erected after April twelfth, nineteen hundred one, which is four stories or less in height and occupied by not more than two families on any story shall either have windows in its public halls as above provided or a stairwell twelve inches or more in width extending from the entrance story to the roof. In such a tenement, except as provided in subdivision four, every entrance door shall contain five square feet or more of glazed surface, and all doors leading from the public halls shall be provided with translucent glass panels five square feet or more in area for each door and fixed transoms of translucent glass over each door.

4. Neither such windows nor such a stairwell shall be required in cities of one million or more population in tenements which do not exceed three stories in height or fifty-five feet in depth and which are occupied by not more than one family on any story and in which the stairs descend in a straight and continuous run from the top story to the entrance story with proper landings at each story. Such tenements shall not be required to have glass panels or transoms in the doors leading from the public halls.

5. In every public hall that is provided with a window or windows in a tenement erected after April twelfth, nineteen hundred one, at least one such window shall be at least two feet six inches wide and five feet high.

6. In every such tenement there shall be provided, at every floor level, a window opening upon a street, yard, court or space above a setback to light and ventilate every stair. Every such required window shall be of the size required by subdivision five, except that a window opening upon a street need be only four feet high. On the top story a ventilating skylight of the same dimensions shall be accepted in lieu of a window for that story.

7. In every such tenement there shall be in the roof, directly over each stairwell, a ventilating skylight provided with ridge ventilators having an opening of at least forty square inches, or provided with fixed or movable louvres. The roof of every such skylight shall have at least twenty square feet of glazed surface. If the stairs and public halls are not provided at each story with windows opening directly to the outer air, the skylights shall be provided with ridge ventilators and also with fixed or movable louvres or movable sashes.

8. A sash door shall be deemed the equivalent of a window for the purposes of this section if it contains the amount of glazed surface prescribed for such windows.

9. In all old-law tenements the public halls and stairs shall be provided with such skylights, ventilators, windows in bulkheads or other means of lighting and ventilation as may be deemed practicable by the department.

10. All skylights installed in old-law tenements after April eighteenth, nineteen hundred twenty-nine, shall be provided with ridge ventilators having an opening of at least forty square inches and also with fixed or movable louvres or with movable sashes. They shall be of such size as may be determined to be practicable by the department, and the roofs of such skylights shall be glazed with plain glass equipped with suitable wire screen above and below.

11. Whenever a public hall in any old-law tenement four stories or more in height is not light enough in the daytime to permit a person to read in every part thereof without the aid of artificial light, every door at the end of such hall or opening therefrom into a room shall have a wire glass panel or panels of an aggregate area of at least four square feet; or in lieu thereof such hall may be lighted by a window or windows opening upon a street or upon a lawful yard, court or shaft, with the plane of each such window at right angles to the length of the hall. In any such tenement any public hall or stair which is not provided with a window opening directly upon a street or yard and which is not sufficiently lighted in the opinion of the department shall be provided by the owner with artificial light, which shall be kept burning at all times.

12. Any part of a public hall that is shut off from any other part of such hall by a door or doors shall be deemed a separate hall for the purposes of this section.