Zoning & Size Limits
| Requirement | Somerville, MA | Quincy, MA |
|---|
| Allowed Zones | By right in Neighborhood Residence (NR) district as the 'Bac | One ADU by right in single-family zoning districts (internal |
| Max Size (Detached) | 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) | 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 |
| Max Size (Attached) | 900 sq ft or 50% of principal dwelling gross floor area, whichever is smaller (state cap); internal conversions (basement/attic) follow the same cap | 900 sq ft or 50% of the principal structure's gross floor area, whichever is less |
| Max Height | Backyard cottage: 1.5 stories max, ground story he | Detached ADUs limited to one story (city guideline |
| Parking Required | None required for the ADU — state law bars parking requireme | 1 additional off-street space required only if the ADU is ou |
| Owner Occupancy | Not allowed — prohibited statewide by the Affordable Homes A | Not allowed — prohibited statewide by the Affordable Homes A |
Setback Requirements
| Setback | Somerville, MA | Quincy, MA |
|---|
| Rear Setback | 3 ft minimum (3 or 20 ft where lot abuts an alley); 10 ft minimum separation from the principal building | Detached ADUs must meet the principal-structure yard setbacks in QZO Table 4.1 — varies by district; Confirm with Quincy Inspectional Services |
| Side Setback | 3 ft minimum | Per QZO Table 4.1 (district-specific) — Confirm with Quincy Inspectional Services |
| Front Setback | Backyard cottages sit behind the principal buildin | Per QZO Table 4.1 (district-specific) — Confirm wi |
Permits & Timeline
| Detail | Somerville, MA | Quincy, MA |
|---|
| Permit Timeline | Building-permit plan review typically 4-8 weeks — Confirm with Inspectional Services (617-625-6600 ext. 5600, isd@somervillema.gov) | Standard building-permit review; typically 4-8 weeks — Confirm with Quincy Inspectional Services |
| Permit Fees | Confirm with Inspectional Services — building permit fees are valuation-based; budget several thousand dollars on a typical $300K+ build | Valuation-based building permit fee — Confirm with Quincy Inspectional Services |
| Impact Fees | None for a single ADU — Confirm with Inspectional Services | None listed in the ADU guidelines — Confirm with Quincy Insp |
| Pre-Approved Plans | None — Somerville does not offer a pre-approved AD | None — Quincy does not offer a pre-approved ADU pl |
Construction Costs
| Cost | Somerville, MA | Quincy, MA |
|---|
| Avg Build Cost | $275,000-$450,000 | $250,000-$425,000 |
| Cost Per Sq Ft | $400-$600 | $350-$550 |
| Garage Conversion | $150,000-$250,000 | $150,000-$250,000 |
| Prefab ADU | $180,000-$350,000 installed (site work, foundations, and buried utilities extra — confirm with manufacturer) | $180,000-$350,000 installed (site work, foundation, and utility connections extra — confirm with manufacturer) |
Rental Income Potential
| Rental | Somerville, MA | Quincy, MA |
|---|
| 1BR Avg Rent | $2,600-$3,000/mo | $2,200-$2,700/mo |
| 2BR Avg Rent | $3,300-$3,700/mo | $2,700-$3,300/mo |
| Short-Term Rentals | Effectively no — Somerville's STR ordinance (registration re | No — Quincy's ADU guidelines expressly prohibit using an ADU |
| Est. ROI | 6-9% annual return | 5-8% annual return |
Which City Is Better for ADUs?
Somerville scores 7/10 while Quincy scores 6/10 on our ADU-friendliness index.
Somerville edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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