Compare ADU zoning rules across 6 Massachusetts cities. Average ADU score: 6.3/10.
| City | Max Size | Setbacks | Permit Fees | Build Cost | 1BR Rent | Score |
|---|---|---|---|---|---|---|
| Boston | Not as-of-right — ZBA variance required (by-right only in Mattapan) | 20 feet (applies to variance/Mattapan detached units) | $4,500-$7,500 | $200,000-$400,000 | $1,800-$2,400/mo | 5/10 |
| Cambridge | 900 sq ft or 50% of primary dwelling, whichever is less (MA state by-right cap) | 5 ft base (ADU setbacks may not be stricter than principal/accessory standards under 760 CMR 71.03) | $3,500-$5,500 | $210,000-$420,000 | $1,900-$2,500/mo | 8/10 |
| Newton | 1,000 sq ft or 50% of the main building by right; 1,200 sq ft in an existing garage or if the owner occupies the site; up to 1,500 sq ft by special permit | 5 ft for a 1.5-story/22-ft detached ADU; standard principal-dwelling setbacks for taller units | Building permit fees based on construction value — Confirm with Newton Inspectional Services | $250,000-$450,000 | $2,500-$3,300/mo | 6/10 |
| Quincy | 900 sq ft or 50% of the principal structure's gross floor area (per 760 CMR 71.02), whichever is less; minimum 320 sq ft for a detached ADU | Detached ADUs must meet the principal-structure yard setbacks in QZO Table 4.1 — varies by district; Confirm with Quincy Inspectional Services | Valuation-based building permit fee — Confirm with Quincy Inspectional Services | $250,000-$425,000 | $2,200-$2,700/mo | 6/10 |
| Somerville | Local backyard cottage: 576 sq ft max floor plate, max massing 24 ft wide x 32 ft deep; state protected-use ADU: up to 900 sq ft or 50% of principal dwelling GFA, whichever is smaller (reasonable local dimensional standards still apply) | 3 ft minimum (3 or 20 ft where lot abuts an alley); 10 ft minimum separation from the principal building | Confirm with Inspectional Services — building permit fees are valuation-based; budget several thousand dollars on a typical $300K+ build | $275,000-$450,000 | $2,600-$3,000/mo | 7/10 |
| Worcester | 900 sq ft by-right (larger is possible via Planning Board special permit) | 5 ft via the accessory-structure standard (R districts) | $2,800-$4,500 | $140,000-$280,000 | $1,250-$1,650/mo | 6/10 |
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