§ 218. Alterations. 1. Any non-fireproof tenement erected after May fifteenth, nineteen hundred two, having apartments extending from street to yard and having one or more outer courts on a side lot line four feet or more in width or inner courts which alone or together with adjoining courts are eight feet or more in width and twelve feet six inches or more in depth, may be altered into apartments opening either on the street or the yard, provided all such altered apartments also have windows opening on such a court. All such altered apartments shall be provided with a second means of egress as required by section two hundred thirty-one. The entrance and stair halls of such tenement shall be fire-retarded.

2. No room in the cellar or basement of any tenement shall be constructed or altered to be occupied for living purposes unless all of the conditions of section thirty-four and of subdivision eight of section twenty-six in regard to multiple dwellings erected after April eighteenth, nineteen hundred twenty-nine, are complied with, except that the minimum depths of yards and courts prescribed for tenements in subdivision one of section two hundred twelve shall be substituted for the minimum depths referred to in section thirty-four.

3. Any additional room or hall constructed or created in a tenement shall comply in all respects with the provisions of this article respecting rooms or halls in tenements erected after April eighteenth, nineteen hundred twelve, except that in any tenement erected after April fourteenth, nineteen hundred three, such rooms or halls may be of the same height as the other rooms or halls on the same story.

4. The number of apartments or suites of rooms on any story in any tenement erected after April twelfth, nineteen hundred one, may be altered so as to increase or decrease the number of living rooms provided such dwelling shall conform with the applicable provisions of sections two hundred thirty-five and two hundred thirty-six.

5. If the number of apartments or suites of rooms in any old-law tenement is increased, the entrance hall and both sides of the walls of the stair halls adjoining the altered apartment shall be fire-retarded, the stairs shall extend to the roof and there shall be no inside stairs from the entrance story to a cellar, or to a basement or other story below the entrance story. However, such inside stair may be permitted provided such stair is constructed of incombustible material, has closed risers, is enclosed between the entrance story and the next lowest story with fireproof materials having a standard fire-resistive rating of at least three hours, and has fireproof doors and door assemblies at the top and bottom with the doors and door assemblies at the top and bottom with the doors self-closing. The soffit of any stair immediately above an inside cellar stair shall be fire-retarded and the jib partitions enclosing such cellar stair at the first story shall be of incombustible material or fire-retarded on both sides with materials having a standard fire-resistive rating of at least one hour.

6. If any old-law tenement shall be so altered as to increase the number of rooms therein by one-third or more, or if such tenement is increased both in number of rooms and in height and after such alteration is more than four stories or parts of stories above the curb level, or if such tenement is over three stories in height and is combined with another old-law tenement and the combined area on any story exceeds three thousand square feet, the stair halls, entrance halls and other public halls of the whole dwelling shall be made to conform to the requirements of subdivision two of section two hundred thirty-three and sections two hundred thirty-four to two hundred thirty-eight inclusive, except that such combined tenements, if over three stories in height, shall have in the roof a fireproof bulkhead with a fireproof self-closing door.

7. In lieu of fire retarding required under subdivision five, there may be installed in public halls an automatic dry pipe valve system or, where halls are heated, an automatic wet pipe system. Where a sprinkler system is installed it shall be equipped on each story with heads in such number and spaced to protect the complete area of the public halls and stairs and shall be constructed, located and arranged on every stair and entrance hall and in every closet opening therefrom in such a manner as the department may require. Such sprinkler system shall be maintained continuously in good repair and serviceable condition.