Lexington, MA Accessory Structures: Tiny Homes (2026)

Middlesex County does not regulate tiny homes. Chapter 48 of the Acts of 1997 abolished the county executive, leaving zoning to the 54 cities and towns. Massachusetts was one of the first six states to adopt the Tiny House Appendix into the state building code, with Appendix Q taking effect on January 1, 2020. Appendix Q applies to dwellings 400 square feet or less on a permanent foundation and sets standards for ceiling height, loft minimum area, loft access stairs/ladders, headroom, treads, risers, handrails, guards, and emergency escape and rescue openings. Appendix Q does not cover tiny houses on wheels (which Massachusetts treats as recreational vehicles, not dwellings). Even with Appendix Q in the building code, a tiny home is only legal in a Middlesex town if the local zoning bylaw permits it: many towns enforce minimum dwelling size (often 600-1,000 sq ft for single-family) or restrict tiny homes to ADUs. The 2024 Massachusetts Affordable Homes Act (Chapter 150 of the Acts of 2024, effective February 2, 2025) now allows ADUs by right statewide in single-family zones up to 900 sq ft or 50% of the principal dwelling, which provides a clearer path for accessory tiny homes. Confirm zoning eligibility with the planning or building department of the specific town (Cambridge, Somerville, Newton, etc.) before designing or buying a tiny home.