521 CMR, § 10.1
The public use and common use spaces of multiple dwellings in existing buildings consisting of 12 or more units in a building, shall be accessible and shall comply with 521 CMR. The public use and common use spaces of multiple dwellings in new construction consisting of three or more units shall comply with 521 CMR. Public and common use spaces are those spaces inside or outside a building that are used by residents and/or visitors. Public use and common use spaces shall include but not be limited to community facilities, meeting rooms, restaurants, recreation spaces, health facilities, pools, public toilet rooms, laundry areas, trash areas, storage areas, mailboxes, walks, sidewalks, parking lots and garages, entrances, elevators, lobbies and foyers, as well as corridors and stairways leading to dwelling units.
521 CMR, § 10.1