The bill amends several sections of Chapter 45-24 of the General Laws, which governs zoning ordinances, by introducing new provisions that clarify the means by which attached single-family dwelling units may be created, recorded, and regulated as subdivisions of an existing lot. Key changes include allowing owners of substandard lots of record with more than one principal dwelling to subdivide the lot so that each dwelling is treated as its own lot, 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. The bill also allows for a zero-lot line setback along the common property line between attached single-family dwelling units.

Additionally, the bill expands the circumstances under which accessory dwelling units (ADUs) may be allowed by right, clarifies the extent to which local authorities can set the maximum size of ADUs in relation to the gross area of the principal dwelling, and ensures the right of municipalities to require year-round occupancy for such units. The maximum unit size regulations for ADUs are specified, allowing 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 defines "gross floor area" and states that nothing in this section shall restrict a municipality's right to require year-round occupancy restrictions for rental ADUs, which are not subject to the thirty-year limitation on restricted covenants. Overall, the bill seeks to streamline the development of ADUs while ensuring compliance with local and state regulations. This act would take effect upon passage.