An existing building or structure that undergoes alteration or a change in use or occupancy and which is located on a public street or fire apparatus access road that has a substandard road width as set forth in FC503.2.10 or 503.3.2 shall install a sprinkler system throughout such building, when:
- The cost of making alterations to the building (other than alterations made to Group R-3 occupancies) in any 12-month period exceeds 60 percent of the value of the building, as set forth in New York City Administrative Code §27-115; or
- By reason of alteration or otherwise, there is a change in the "main use or dominant occupancy" of the building, as determined by the New York City Department of Buildings for purposes of assigning a single occupancy classification to the building, including any change from a Group R-3 occupancy to a Group R-2 occupancy, but excluding a change in use or occupancy that is limited to restoring a building that was originally constructed as a one-family or two-family dwelling to its original one-family or two-family use and occupancy; or
- There is an increase of more than 125 percent in the square footage of the floor area of a building (excluding attic, basement and cellar space, as those terms are defined in Section 202 of the Building Code); or
- There is a change constituting an alteration under the Building Code (excluding rooftop equipment installations) to a building of combustible (non-fireproof) construction with a height of 35 feet (10 668 mm) or less above the grade plane, that increases the height of such building to more than 35 feet (10 668 mm) above the grade plane (with the terms "grade plane" and "building height" having the meanings set forth in Section 502.1 of the Building Code); or
- A one-family Group R-3 occupancy is being altered to a two-family Group R-3 occupancy, except where:
- the alteration involves converting a basement space to a separate dwelling unit, and the new basement dwelling unit is protected throughout by a sprinkler system; or
- the alteration does not involve converting a basement space to a separate dwelling unit, and either at least two lawful accessory off-street parking spaces are provided on the premises, or sufficient space exists to park two motor vehicles on a common driveway shared exclusively with an adjoining Group R-3 occupancy.