Section 3 of said chapter 40A, as appearing in the 2016 Official Edition, is hereby amended by adding the following paragraph:-

No zoning ordinance or by-law shall prohibit or require a special permit for the use of land or structures for an accessory dwelling unit located internally within a single-family dwelling or the rental thereof on a lot not less than 5,000 square feet or on a lot of sufficient area to meet the requirements of title 5 of the state environmental code established by section 13 of chapter 21A, if applicable; provided, however, that such land or structures may be subject to reasonable regulations concerning dimensional setbacks, screening and the bulk and height of structures. The zoning ordinance or by-law may require that the principal dwelling or the accessory dwelling unit be continuously owner-occupied and may limit the total number of accessory dwelling units in the municipality to not less than 5 per cent of the total non-seasonal single-family housing units in the municipality. Not more than 1 additional parking space shall be required for an accessory dwelling unit; provided, however, that, if parking is required for the principal dwelling, that parking shall be retained or replaced. Exterior alterations of the principal dwelling to allow separate primary or emergency access to the accessory dwelling unit shall be allowed without a special permit if such alterations are within applicable dimensional setback requirements. Nothing in this paragraph shall authorize an accessory dwelling unit to violate or avoid compliance with the building, fire, health or sanitary codes, historic or wetlands laws, ordinances or by-laws or title 5 of the state environmental code established by said section 13 of said chapter 21A, if applicable. This section shall not limit a city or town’s authority to prohibit or restrict use of an accessory dwelling unit as a short-term rental.