105 CMR 410.430
Natural Light and Obstructions
(A) The owner shall provide transparent or translucent glass which admits unobstructed light
from the outdoors equal in area to a minimum 8% of the entire floor area in:
(1) Habitable rooms other than a kitchen.
(2) Kitchens which have a floor area greater than 70 square feet.
(B) If any light obstructing structure is located less than three feet from the outside of and
extends to a level above the lower level of the transparent or translucent glass, that portion so
obstructed shall not be included as contributing to the required minimum total glass area.