Lexington MA’s zoning code permits Accessory Dwelling Units (ADUs) so long as they are located in the principle dwelling, the gross floor area does not exceed 1,000 square feet, and there are no more than two bedrooms.
ADUs help increase neighborhood densities, which diminishes demand for automobile travel. ADUs, being smaller than traditional single-family homes, also consume fewer natural resources in the construction process as well as the during the day-to-day operation of the unit.