The 421-b tax incentive is a partial tax exemption for new construction, conversion, or renovation of owner-occupied one- and two-family homes and certain multiple dwellings. 421-b is not available to three- and four-unit multiple dwellings that were completed after 2008 and one- and two-family homes that were completed after 2011.
Contact 421a_customerservice@hpd.nyc.gov for more information.