Section 9. Buildings converted or altered

1.  On  or  after  December
  fifteenth, nineteen hundred sixty-one, no  multiple  dwelling  shall  be
  enlarged  or  its  lot  diminished  so that the yard or other unoccupied
  areas shall be  less  in  size  or  area  than  the  minimum  dimensions
  prescribed in section twenty-six.
    2.  A  building  not  a  dwelling, if converted or altered after April
  eighteenth, nineteen hundred twenty-nine, to a multiple dwelling,  shall
  thereupon   become  subject  to  all  the  provisions  of  this  chapter
  applicable to dwellings of like class and kind erected after such date.
    3. A dwelling of one class or kind, altered or converted  after  April
  eighteenth,  nineteen  hundred  twenty-nine,  to  another class or kind,
  except as hereinafter in this section and  in  articles  six  and  seven
  otherwise provided, shall thereupon become subject to all the provisions
  of  this chapter applicable to a building of that class or kind, erected
  after such date, to which it is altered or converted.
    4. No dwellings shall be altered so as  to  be  in  violation  of  any
  provision  of  this chapter relating to dwellings of like class and kind
  erected after April eighteenth,  nineteen  hundred  twenty-nine,  except
  that  it  shall  be  sufficient  for  the  purposes of this section that
  tenements shall comply with article seven,  converted  dwellings  comply
  with  article  six,  and  lodging  houses comply with section sixty-six.
  Nothing in this section  shall,  however,  be  deemed  to  prohibit  the
  conversion  or  alteration  of  any  multiple  dwelling,  other  than  a
  converted dwelling and a lodging house, from a class  A  to  a  class  B
  multiple  dwelling,  or vice-versa, provided that the entire dwelling is
  of fireproof construction and is  made  to  conform  to  the  applicable
  provisions  of  section sixty-seven, and to all other provisions of this
  chapter applicable to multiple dwellings of like class and kind  erected
  before April eighteenth, nineteen hundred and twenty-nine.
    5.  a.  Any  multiple  dwelling  may  be  altered  to conform with any
  provision of this chapter applicable to dwellings of like class and kind
  and not expressly limited in  application  to  dwellings  erected  after
  April  eighteenth,  nineteen  hundred  twenty-nine; or to conform to the
  provisions of  this  chapter  relating  to  egress,  or  to  exits  from
  apartments,  in dwellings of like class and kind erected after such date
  if such dwelling also  conforms  or  is  made  to  conform  to  all  the
  requirements  relating  to  stairs and public halls in dwellings erected
  after such date, except that  existing  dimensions  of  stair  landings,
  treads and risers need not be changed.
    b.  An  apartment in any part of a fireproof multiple dwelling erected
  before April eighteenth, nineteen hundred twenty-nine, may be altered or
  subdivided and need not conform to the requirements of  paragraph  a  of
  this  section  relating  to  stairs and public halls provided each newly
  created apartment has access to a public hall which provides  horizontal
  egress  to  at least two stairs. If both of such stairs are not arranged
  and designed as required by sections  two  hundred  thirty-six  and  two
  hundred  thirty-seven,  at least one of such stairs shall be so arranged
  and designed, and the other shall be arranged and designed  as  required
  by  section  two  hundred thirty-nine. Both stairs shall be protected by
  automatic sprinkler heads throughout.
    6. Any tenement previously converted to other uses may be  altered  or
  reconverted  to  a  tenement by complying with the provisions of article
  seven, provided, however, that its height and  bulk  were  not  enlarged
  prior  to  such alteration or reconversion except as permitted by and in
  accordance with the provisions of sections two hundred  eleven  and  two
  hundred twelve of this chapter.
    7. In any class B multiple dwelling, except a rooming house or lodging
  house,  any  apartment  may  be  occupied  as  an apartment in a class A

  multiple  dwelling,  provided  such  apartment  complies  with  all  the
  requirements  for apartments in class A multiple dwellings erected after
  April eighteenth, nineteen hundred twenty-nine. In any rooming house  or
  lodging  house, one apartment may be occupied as an apartment in a class
  A multiple dwelling, provided such apartment is occupied solely  by  the
  owner, janitor, superintendent or caretaker.
    8.  Any apartment in any class A multiple dwelling may be occupied for
  single room occupancy only if such dwelling complies with the provisions
  of section two hundred forty-eight and  all  other  provisions  of  this
  chapter applicable to such dwelling.
    9.  Excepting  a frame dwelling, any dwelling three stories or less in
  height erected after April eighteenth, nineteen hundred twenty-nine as a
  one or two-family dwelling may be converted to a multiple dwelling to be
  occupied by not  more  than  three  families  in  all,  with  a  maximum
  occupancy  of two families on each floor in a two story building and one
  family on each floor in a three story building, provided however that it
  shall be unlawful for any such dwelling  converted  at  any  time  since
  October  fifteenth,  nineteen hundred fifty-two, to have any boarders or
  roomers. In each such instance, compliance shall be  required  with  all
  the  provisions  of article six, including section one hundred seventy-a
  of said article.
    10. If any class A dwelling erected before April eighteenth,  nineteen
  hundred  twenty-nine,  is altered so as to increase the number of living
  rooms by more than twenty per centum, such dwelling, except as otherwise
  provided in sections two hundred eighteen, two hundred  thirty-five  and
  two  hundred thirty-six, shall be made to conform to the requirements of
  this chapter with respect to class A dwellings of like  class  and  kind
  erected after such date.