Section 6. (a) A proposed smart growth zoning district or starter home zoning district shall satisfy the following minimum requirements:

(1) Each proposed district shall be located in an eligible location.

(2) The zoning for each proposed smart growth zoning district shall provide for residential use to permit a mix of housing for families, individuals, persons with special needs and the elderly.

(3) Housing density in a proposed smart growth district shall be at least: 20 units per acre for multi-family housing on the developable land area, 8 units per acre for single-family homes on the developable land area, and 12 units per acre for 2 and 3 family buildings on the developable land area. Housing density in a proposed starter home district shall satisfy the following criteria: (a) the density shall be no less than 4 units per acre of developable land area; (b) the development shall emphasize smart growth principles of development, such as cluster development and other forms of development providing for common open space usable for passive or active recreational activities, or the use of low-impact development techniques; and (c) at least 50 per cent of the starter homes to be developed in a proposed starter home district, excluding accessory dwelling units, must contain 3 or more bedrooms.

(4) The zoning ordinance or by-law for each proposed smart growth zoning district shall provide that not less than 20 per cent of the residential units constructed in projects of more than 12 units shall be affordable housing and shall contain mechanisms to ensure that not less than 20 per cent of the total residential units constructed in each proposed district shall be affordable housing.

(5) The zoning ordinance or by-law for each proposed starter home zoning district shall provide that, as a condition of the increased density permitted in a starter home zoning district, not less than 20 per cent of the residential units created as starter homes shall be affordable to and occupied by individuals and families whose annual income is less than 100 per cent of the area median income as determined by the United States Department of Housing and Urban Development, and shall contain mechanisms to ensure that the required percentage of the total residential units constructed in each proposed starter home district shall meet such affordability requirements, including an affordable housing restriction, as defined in section 31 of chapter 184, that has a term of not less than 30 years.

(6) A proposed smart growth zoning district shall permit infill housing on existing vacant lots and shall allow the provision of additional housing units in existing buildings, consistent with neighborhood building and use patterns, building codes and fire and safety codes.

(7) A proposed smart growth zoning district or starter home zoning district shall not be subject to limitation of the issuance of building permits for residential uses or a local moratorium on the issuance of such permits. In addition, a proposed starter home zoning district shall not be subject to any municipal environmental or health ordinances, bylaws or regulations that exceed applicable requirements of state law or regulation, unless the department of environmental protection has determined that specific local conditions warrant imposition of more restrictive local standards, or the imposition of such standards would not render infeasible the development contemplated under the comprehensive housing plan, housing production plan or housing production summary submitted as part of the application for such district.

(8) A proposed smart growth zoning district or starter home zoning district shall not impose restrictions on age or any other occupancy restrictions on the district as a whole. This shall not preclude the development of specific projects within a smart growth zoning district that may be exclusively for the elderly, the disabled or for assisted living. Not less than 25 per cent of the housing units in such a project within a smart growth zoning district shall be affordable housing, as defined in section 2.

(9) Housing in a smart growth zoning district or starter home zoning district shall comply with federal, state and local fair housing laws.

(10) A proposed smart growth zoning district or starter home zoning district may not exceed 15 per cent of the total land area in the city or town. Upon request, the department may approve a larger land area if such approval serves the goals and objectives of this chapter.

(11) The aggregate land area of all approved smart growth zoning districts and starter home zoning districts in the city or town may not exceed 25 per cent of the total land area in the city or town. The department may approve a larger combined land area if the department determines that such approval serves the goals and objectives of this chapter.

(12) Housing density in any proposed district shall not over burden infrastructure as it exists or may be practicably upgraded in light of anticipated density and other uses to be retained in the district.

(13) A proposed smart growth zoning district or starter home zoning district ordinance or by-law shall define the manner of review by the approving authority in accordance with section 11 and shall specify the procedure for such review in accordance with regulations of the department.

(b) A city or town may modify or eliminate the dimensional standards contained in the underlying zoning in the smart growth zoning district or starter home zoning district ordinance or by-law in order to support desired densities, mix of uses and physical character. The standards that are subject to modification or waiver may include, but shall not be limited to; height, setbacks, lot coverage, parking ratios and locations and roadway design standards. Modified requirements may be applied as of right throughout all or a portion of the smart growth zoning district or starter home zoning district, or on a project specific basis through the smart growth zoning district or starter home zoning district plan review process as provided in the ordinance or by-law. A city or town may designate certain areas within a smart growth zoning district or starter home zoning district as dedicated perpetual open space through the use of a conservation restriction as defined in section 31 of chapter 184 or such other means as may be created by state law. The amount of such open space shall not be included as developable land area within the smart growth zoning district or starter home zoning district. Open space may include an amount of land equal to up to 10 per cent of what would otherwise be the developable land area if the developable land would be less than 50 acres, and 20 per cent of what would otherwise be the developable land area if the developable land area would be 50 acres or more.

(c) The zoning for a proposed smart growth zoning district may provide for mixed use development.

(d) A smart growth zoning district or starter home zoning district may encompass an existing historic district or districts. A city or town, with the approval of the department, may establish a historic district in an approved smart growth zoning district or starter home zoning district in accordance with chapter 40C, so long as the establishment of the historic district meets the requirements for such a historic district and does not render the city or town noncompliant with this chapter, as determined by the department. The historic districts may be coterminous or non-coterminous with the smart growth zoning district or starter home zoning district. Within any such historic district, the provisions and requirements of the historic district may apply to existing and proposed buildings.

(e) A city or town may require more affordability than required by this chapter, both in the percentage of units that must be affordable, and in the levels of income for which the affordable units must be accessible, provided, however, that affordability thresholds shall not unduly restrict opportunities for development.

(f) With respect to a city or town with a population of fewer than 10,000 persons, as determined by the most recent federal decennial census, for hardship shown, the department may, pursuant to regulations adopted under this chapter, approve zoning for a smart growth zoning district with lower densities than provided in this chapter, if the city or town satisfies the other requirements set forth in this section; provided, however, that such approval shall not be withdrawn solely because, in a future census, the population of the city or town exceeds 10,000 persons.

(g) Any amendment or repeal of a zoning ordinance or by-law affecting an approved smart growth zoning district or starter home zoning district shall not be effective without the written approval by the department. Each amendment or repeal shall be submitted to the department with an evaluation of the effect on the city or town's comprehensive housing plan or housing production plan, if any. Amendments shall be approved only to the extent that the district remains in compliance with this chapter. If the department does not respond to a complete request for approval of an amendment or repeal within 60 days of receipt, the request shall be deemed approved.

(h) Nothing in this chapter shall affect a city or town's authority to amend its zoning ordinances or by-laws under chapter 40A, so long as the changes do not affect the smart growth zoning district or starter home zoning district.