Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 40R, § 13

A city or town may apply to the department for approval of an existing zoning district as a smart growth zoning district if it meets the requirements for such a district, including the affordability requirements and the density requirements. The application shall be the same as for a new smart growth zoning district. Upon approval, a city or town with an existing district shall become entitled to the one-time density bonus payments upon the construction of new units within the smart growth zoning district and preference of capital expenditure funds, as provided in section 9, from the date of approval, but shall not be eligible for zoning incentive payments.