Accessory Dwelling Units (ADU)
Case Study

Lexington, MA

Lexington is a fairly affluent community located in close proximity to Boston and with ready access to Routes 2 and 128. The community has an exceptionally strong school system that has fostered residential growth. The birthplace of the American Revolution, Lexington is a popular tourist destination and the site of many annual events. The town lies within an area of similar communities struggling to maintain their suburban nature in the face of strong real estate market demands and growth.

Historic building in Lexingtown, MA.

Lexington is a highly built-out suburb with strong demand for housing. Lexington implemented its first accessory dwelling unit bylaw in 1983, since then only 60 units have been constructed. In February 2005, the Town amended the ADU bylaws in order to simplify the bylaws and enable the development of more accessory units. Changes made included:
- Reducing or eliminating minimum lot size or floor area requirements;
     - Allowing ADUs by-right in homes built as recently as five years ago; and
     - Allowing ADUs by Special Permit in new construction

Why it works:

  • Market Constraints - Land for new construction in Lexington is extremely limited and demand for housing is high. The need for accessory units will increase out of necessity; the zoning bylaws allow the existing housing market to fill this demand sustainably.
  • Clarity of Bylaws - Lexington amended its ADU bylaws in 2005 in order to improve the clarity of the provisions. The improved transparency eliminates attitudinal barriers to constructing accessory units by making the regulations clear and intuitive.
  • Flexibility - Accessory units can be constructed by-right, by special permit, or as accessory apartments in accessory structures. The clear definition of each development option expands the number of homeowners able and willing to construct accessory units.
  • Comprehensive Planning - Lexington's ADU provisions match the goals articulated in the city's comprehensive plan, which include increasing the supply of affordable housing and providing housing for middle-income households that are being priced out of the city's housing market.