SECTION 1. Section 2 of chapter 40R of the General Laws, as appearing in the 2014 Official Edition, is hereby amended by inserting after the word “meanings:,” in line 2,  the following definitions:-

“Accessory dwelling unit”, a self-contained housing unit incorporated within a single-family dwelling or detached accessory structure that is clearly subordinate to the single-family dwelling and complies with the use, dimensional, and design requirements of the local zoning ordinance or by-law.

“Accessory dwelling zoning district”, a zoning district adopted by a city or town pursuant to this chapter that is superimposed over 1 or more zoning districts, in which a developer may elect to (i) develop a project in accordance with requirements of the accessory dwelling zoning district ordinance or bylaw, or (ii) develop a project in accordance with requirements of the underlying zoning district.

SECTION 2. Said chapter 40R is hereby further amended by adding the following section:-

Section 15. In its zoning ordinance or by-law, a city or town may adopt an accessory dwelling zoning district. A proposed accessory dwelling zoning district shall permit the use of accessory dwelling units as of right.

No zoning ordinance or by-law shall unreasonably regulate the location, dimensions, or design of an accessory dwelling unit on a lot.

An accessory dwelling zoning district ordinance or by-law, or any amendment to or repeal of such ordinance or by-law, shall be adopted in accordance with section 5 of chapter 40A; provided however, that an accessory dwelling zoning district ordinance or bylaw shall be adopted, amended or repealed by a simple majority vote of all the members of the town council, or of the city council where there is a commission form of government or a single branch, or of each branch where there are 2 branches, or by a simple majority vote of a town meeting.

A city or town with an approved accessory dwelling zoning district shall not be eligible for a zoning incentive payment or a density bonus payment pursuant to section 9, unless the district meets the requirements of an approved smart growth zoning district pursuant to section 6 of this chapter.”.