§ 231. Egress. 1. Every non-fireproof tenement exceeding two stories in height and every fireproof tenement erected after May sixteenth, nineteen hundred thirteen, shall have at least two independent means of egress, which shall extend from the ground story to the roof, be located remote from each other and be separated from each other by walls.

2. One of such means of egress shall be a flight of stairs constructed as provided in sections two hundred thirty-three to two hundred thirty-eight inclusive; but this sentence shall not be construed to require any alteration in the material or width of any stair or its treads and risers lawfully permitted on April eighteenth, nineteen hundred twenty-nine.

3. The other required means of egress shall be directly accessible at each story to each apartment without having to pass through the first means of egress. Such other means of egress shall be any one of the following, as the owner may elect:

a. A system of outside fire-escapes constructed as provided in section fifty-three.

b. An additional stair, either inside or outside, constructed and arranged as provided in sections two hundred thirty-three to two hundred thirty-eight inclusive.

c. A fire-tower or fire-stair constructed and arranged as provided in section two hundred thirty-nine.

d. Except as provided in subdivision nine of section fifty-three, any means of egress lawfully permitted on April eighteenth, nineteen hundred twenty-nine, except wire, chain, cable, vertical ladder, or rope fire-escapes.