Everything homeowners ask about building an ADU in Medford — answered with 2026 data.
Yes, ADUs are allowed in SF-1, SF-2, GR, APT-1 and APT-2 — every district where a detached single-family dwelling is a permitted use (Table A, row A.1). 760 CMR 71.02 defines a "Single-family Residential Zoning District" as any district where single-family dwellings are permitted or allowable, so the protection is not confined to SF-1 and SF-2. None arises in ROS, APT-3, C-1, C-2, I, O, O-2, MUZ or the new Mystic Avenue, Salem Street and Medford Square districts (single-family is N there). Confirm at (781) 393-2480. in Medford, MA. The maximum size for a detached ADU is The smaller of 900 sq ft or half the principal dwelling's gross floor area. Medford § 94-8.2.3(4) and M.G.L. c. 40A § 1A / 760 CMR 71.02 agree on the number. Under 760 CMR 71.02, GFA counts every story of compliant ceiling height including basements and lofts but excludes crawl spaces, garages, attics and enclosed porches — so a 1,400 sq ft house gets a 700 sq ft unit. § 94-8.2.3(4) lets the Board exceed 900 sq ft only for a carriage house or barn with preservation value, by special permit. Attached ADUs can be up to Same cap — the smaller of 900 sq ft or half the house's gross floor area. Medford has an ADU-friendliness score of 7/10. Check our full Medford ADU rules page for complete zoning details.
ADU construction in Medford typically costs $220,000-$400,000. The cost per square foot averages $275-$450. Garage conversions are more affordable at $100,000-$250,000, while prefab ADUs cost $250,000-$525,000. Permit fees add $15.00 per $1,000 of estimated construction cost plus a $35.00 application fee, a $100.00 plan review fee for 1-4 family dwellings and $125.00 for a certificate of occupancy (Schedule of Building Fees effective July 28, 2009; Code Appendix A, § 10-35) — about $3,885 on a $250,000 ADU. to your budget. See our detailed Medford ADU cost guide.
Detached ADUs in Medford can be up to The smaller of 900 sq ft or half the principal dwelling's gross floor area. Medford § 94-8.2.3. Attached ADUs are limited to Same cap — the smaller of 900 sq ft or half the house's gross floor area. Junior ADUs (JADUs) have a cap of Not a category in Massachusetts — no junior ADU exists in M.G.L. c. 40A, 760 CMR 71.00 or the Medford Zoning Ordinance. A unit carved out of the existing house is simply an ADU under the same 900 sq ft / half-GFA cap. Maximum height is 35 ft and 2½ stories for a dwelling in every residential district (Table B, row 1). Medford limits structures accessory to one- and two-family dwellings to 15 ft (§ 94-4.3.1(1)), but 760 CMR 71.03(3)(b)(2) bars any height or story standard stricter than the more permissive of the principal-dwelling and accessory-structure standards, which is 35 ft. The city has published no determination on this; confirm with the Building/Zoning Department at (781) 393-2509 before drawing a second story. You are allowed up to One. § 94-8.2.3 on a qualifying lot.
Rear setback: 3 ft for a detached ADU, or 1 ft with fire-resistance-rated wall assemblies (§ 94-4.3.2(3), accessory structures). A dwelling needs a 15 ft rear yard (Table B, row 1), but 760 CMR 71.03(3)(b)(2) gives the ADU the more permissive of the two. An accessory building may occupy up to 25 percent of the rear yard (§ 94-4.2.5(1)) and must sit at least 10 ft from the house and from any other accessory building (§ 94-4.1.2(3)(a)). Side setback: 3 ft from the side lot line for a detached ADU, or 1 ft with fire-resistance-rated walls (§ 94-4.3.2(3)) — more permissive than the 7½ ft side yard Table B requires of the house, so it governs under 760 CMR 71.03(3)(b)(2). § 94-4.3.2(1): in residential districts no accessory structure may stand in the required front or side yard, so a detached unit belongs in the rear yard. An attached ADU takes the house's own 7½ ft side yard. Front setback: 15 ft for the principal dwelling in all residential districts (Table B, row 1). A detached ADU may not be placed in the required front yard at all (§ 94-4.3.2(1)); an interior or attached unit uses the house's 15 ft front yard. Off-street parking may not be placed in the front yard in SF-1, SF-2 and GR (§ 94-6.1.4(3)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
Usually none; at most one space. § 94-8.2.3(7) asks for "no more than one additional parking space, when necessary and feasible"; 760 CMR 71.03(2)(b) caps it at one and bars any space if any part of the lot is within 0.5 mile of a Transit Station, which 760 CMR 71.02 defines to include a Bus Station — any embarkation point for an MBTA bus. Wellington, Medford/Tufts, Ball Square and West Medford stations and the bus network cover most of the city; Table A's 2 spaces per unit binds the house only. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. § 94-8.2.3(2) still demands an affidavit that one of the two units is owner-occupied, and § 94-8.2.3(8) expires the permit every five years without a fresh affidavit; the Building Department's ADU handout (September 7, 2022, still posted) repeats both. State law overrides them: M.G.L. c. 40A § 3 bars owner-occupancy requirements, 760 CMR 71.03(2)(a) lists them first among Prohibited Regulations, and 71.03(4) bars enforcing such a condition even if imposed before January 31, 2025. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Medford is typically The Building Department's FAQ says the building official has 30 days to review and act on a building permit application and that most reviews finish sooner; new buildings go to the weekly Tuesday development meeting for multi-department sign-off. No ADU-specific timeline is published. Plan check: Standard building plan review ($100.00 plan review fee, 1-4 family dwellings). Two Massachusetts items to settle early: Title 5 — if the lot is on septic, 310 CMR 15.000 applies through the Board of Health and the § 94-8.2.3(1) plot plan must show the system; and utilities — 760 CMR 71.03(3)(b)(3) says the city may not require a separate water, sewer or electric connection, though the utility or a state board still can. Work started without a permit is charged a quadruple fee (Appendix A, § 10-35(10)). Every ADU must be assigned an address to the MassGIS standard and reported to MassGIS and EOHLC (760 CMR 71.03(8)). Pre-approved plans availability: None from the City of Medford — no plan gallery appears on the Building Department or Planning pages as of September 20, 2026. EOHLC's Accessory Dwelling Units page on mass.gov is the state's ADU resource hub; check it for plan and financing material before commissioning a custom set.
Average ADU rental income in Medford: 1-bedroom units rent for $2,500-$2,800/month, 2-bedroom units for $3,000-$3,350/month. Short-term rentals: No — 30-day minimum rental term for the ADU or the house (§ 94-8.2.3(6)); state law lets a city restrict short-term rental of an ADU (M.G.L. c. 40A § 3; 760 CMR 71.03(3)(c)). Long-term letting of both units is allowed. Expected ROI: 6-10% net annual yield (estimate: $220,000-$400,000 build, $2,500-$3,350/mo HUD-based rent, before financing).
The minimum lot size for an ADU in Medford is None for the ADU — 760 CMR 71.03(3)(b)(2) says a municipality "may not require a minimum Lot size for a Protected Use ADU." The district minimum for the house itself is 7,000 sq ft in SF-1 and 5,000 sq ft in every other district, with 35 ft frontage, 50 ft width, 55 ft depth and 40 percent maximum lot coverage (Table B, row 1). A nonconforming lot or house is not a bar: 760 CMR 71.03(3)(b)(9). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Medford, a garage conversion typically costs $100,000-$250,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
Tell us about your project and we'll pass it to ADU builders serving Medford. Free, no obligation — you choose who to work with. We don't have builders in every area yet; if nobody covers yours, we'll email you to say so.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
Just browsing? Search ADU builders near you by ZIP code.