1. In every multiple dwelling erected after April eighteenth, nineteen hundred twenty-nine, one at least of the required windows provided to light each public hall or part thereof shall be at least two feet six inches wide and five feet high. Every required window in such a hall shall open upon a street, court, yard or space above a setback. On the top story of such a dwelling a ventilating skylight of the same dimensions shall be accepted in lieu of a window for that story.
2. In every multiple dwelling erected after April eighteenth, nineteen hundred twenty-nine, there shall be in the roof, directly over each required stair, fire-stair and fire-tower, a ventilating skylight provided with ventilators having a minimum opening of forty square inches or with fixed or movable louvres. The roof of every such skylight shall be glazed with plain glass and equipped with suitable wire screens above and below. The glazed area of every such skylight shall be at least twenty square feet, except that in a class A dwelling or section thereof two stories or less in height and occupied by not more than two families on each story and in dwellings three stories in height erected pursuant to plans filed with the department on or after May first, nineteen hundred fifty-nine and occupied by not more than one family on each story, the glazed area of such a skylight need be only nine square feet. In lieu of a skylight a window of the same area as prescribed in subdivision one may be provided. If such a window is used in lieu of a skylight, fixed louvres having a minimum opening of forty square inches shall also be installed in or directly adjacent to such window.
3. When any stair, fire-stair or fire-tower in such a dwelling terminates at the level of a setback of an outer wall and such setback consists of a terrace at least four feet in width, measured between the inside of the parapet wall and the wall of the building, and at least ten feet in length, measured parallel to the wall of the building, there may be provided in lieu of such a skylight a fireproof door and assembly with the door self-closing giving access from such stair, fire-stair or fire-tower to such terrace. Such door shall have a panel at least five square feet in area glazed with wire glass and shall be equipped with fixed or movable louvres with an opening of at least forty square inches.