The bill amends several sections of Chapter 45-24 of the General Laws, focusing on zoning ordinances to enhance land use and development regulations. Key provisions include clarifying the means by which attached single-family dwelling units may be created, recorded, and regulated as subdivisions of an existing lot under current zoning ordinance law. It allows owners of a substandard lot of record with more than one principal dwelling to subdivide the lot such that each dwelling is treated as its own lot without requiring zoning relief for dimensional nonconformities. The zoning ordinance must allow each attached single-family dwelling unit to be located on its own lot through the subdivision of an existing property, at permitted levels of density, and without specific requirements for maximum building lot coverage or minimum lot size, lot width, lot frontage, or lot depth for the individual lots resulting from subdivision.

Additionally, the bill expands the circumstances in which an accessory dwelling unit (ADU) may be allowed by right, clarifying that municipalities may establish maximum unit size regulations for ADUs, which must allow for a studio or one-bedroom ADU of up to 900 square feet or 60% of the gross floor area of the principal dwelling, whichever is less, and for an ADU with two bedrooms or more, up to 1,200 square feet or 60% of the gross floor area of the principal dwelling, whichever is less. The bill also ensures that the gross floor area has the same meaning as set forth in the state building code and retains municipalities' rights to impose year-round occupancy restrictions on ADUs offered for rental occupancy.

The act takes effect upon passage.