Cambridge is moderately progressive on ADU regulations, allowing accessory units in residential zones with reasonable size limits. The city's focus on housing affordability and proximity to Boston make it attractive for ADU development.
Zoning & Size Requirements [1][2]
Yes, you can build an ADU in Cambridge. A detached ADU can be up to 900 sq ft under current Massachusetts and Cambridge zoning rules.
| Allowed Zones | All residential districts - Cambridge eliminated single-family-only zoning in Feb 2025 (Residence C-1 citywide); one ADU is by-right under the state law |
| Max Size (Detached) | 900 sq ft or 50% of primary dwelling, whichever is less (MA state by-right cap) |
| Max Size (Attached) | 900 sq ft or 50% of primary dwelling, whichever is less (MA state by-right cap) |
| Max Size (JADU) | N/A (Massachusetts has no JADU category) |
| Max Height | No ADU-specific cap - an ADU may match the principal-dwelling/accessory standards (base residential height is now 4 stories citywide) |
| Max Units | 1 ADU per lot |
Setback Requirements [1][2]
Cambridge requires a rear setback of about 5 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 5 ft base (ADU setbacks may not be stricter than principal/accessory standards under 760 CMR 71.03) |
| Side Setback | 5 ft base |
| Front Setback | 10 ft base |
| Parking Required | None - Cambridge abolished all parking minimums citywide in Oct 2022 (state law would otherwise allow 1 space beyond 0.5 mi of transit) |
| Owner Occupancy | Not required (prohibited under MA Affordable Homes Act / 760 CMR 71) |
| Min Lot Size | None - state law prohibits a minimum lot size for a by-right ADU (760 CMR 71.03) |
Permit Process & Fees
An ADU permit in Cambridge typically costs $3,500-$5,500 and takes 60-90 days, through a standard permit review.
| Approval Process | Building permit - as-of-right, no discretionary design review |
| Review Timeline | 60-90 days |
| Permit Fees | $3,500-$5,500 |
| Impact Fees | $1,500-$2,500 |
| Plan Check | 3-4 weeks |
| Pre-Approved Plans | Not available |
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Construction Costs [3][4]
Building an ADU in Cambridge typically costs $210,000-$420,000 ($220-$440 per sq ft); a garage conversion runs $105,000-$230,000.
| Average Build Cost | $210,000-$420,000 |
| Cost per Sq Ft | $220-$440 |
| Garage Conversion | $105,000-$230,000 |
| Prefab ADU (Installed) | $160,000-$340,000 |
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Rental Income Potential [5][6]
A 2-bedroom ADU in Cambridge rents for around $2,300-$3,400/mo, an estimated 5-7% annual return.
| Avg Rent (1 Bedroom) | $1,900-$2,500/mo |
| Avg Rent (2 Bedroom) | $2,300-$3,400/mo |
| Short-Term Rental | Not permitted |
| Est. Annual ROI | 5-7% annual return |
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Recent Law Changes
What's Changed Recently
- MA Affordable Homes Act ADU by-right effective Feb 2, 2025 (regulations 760 CMR 71 issued Jan 31, 2025): one ADU allowed by-right in single-family zones statewide, up to 900 sq ft or 50% of the primary dwelling, whichever is smaller
- Owner-occupancy requirements and ADU-specific parking minimums are prohibited; no parking may be required for ADUs within 0.5 mile of a transit station
- Statewide, 1,224 ADUs approved across 217 communities in the law's first year (Gov. Healey, 2026)
- Cambridge's local zoning is overridden by the state Protected Use ADU framework where local rules are more restrictive
Tips for Building an ADU in Cambridge
- Cambridge's university presence (MIT, Harvard) creates strong rental demand
- Design review adds time but ensures quality neighborhood integration
- Premium rents despite lower ROI make Cambridge attractive for long-term hold
- Walkable neighborhoods command premium rental rates
ADU Builders in Cambridge
Looking for an ADU builder in Cambridge? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Cambridge homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Accessory Dwelling Units — Mass.gov (EOHLC) Government Data — Accessed 2026-06-28
- 760 CMR 71.03 — Regulation of Protected Use ADUs in Single-family Residential Zoning Districts Government Data — Accessed 2026-06-28
- Angi — ADU Construction Cost Data Market Data — Accessed 2026-02-24
- Angi — Local ADU Contractor Costs Market Data — Accessed 2026-02-24
- Zillow Rental Manager — Market Rent Data Market Data — Accessed 2026-02-24
- HUD Fair Market Rents Government Data — Accessed 2026-02-24
- Accessory Dwelling Units — Mass.gov Government Data — Accessed 2026-02-24
- Massachusetts Affordable Homes Act — ADU Provisions Government Data — Accessed 2026-02-24
Frequently Asked Questions
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