Zoning & Size Limits
| Requirement | Somerville, MA | Worcester, MA |
|---|
| Allowed Zones | By right in Neighborhood Residence (NR) district as the 'Bac | All zoning districts - by-right on any lot with a lawfully e |
| 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 by-right (larger is possible via Planning Board special permit) |
| 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 by-right (larger via special permit) |
| Max Height | Backyard cottage: 1.5 stories max, ground story he | No ADU-specific cap - the most permissive of the d |
| Parking Required | None required for the ADU — state law bars parking requireme | No additional parking required for an ADU (existing required |
| Owner Occupancy | Not allowed — prohibited statewide by the Affordable Homes A | Not required (owner need not live on the property; prohibite |
Setback Requirements
| Setback | Somerville, MA | Worcester, MA |
|---|
| Rear Setback | 3 ft minimum (3 or 20 ft where lot abuts an alley); 10 ft minimum separation from the principal building | 5 ft via the accessory-structure standard (R districts) |
| Side Setback | 3 ft minimum | 5 feet |
| Front Setback | Backyard cottages sit behind the principal buildin | ADUs may not be placed in the front yard |
Permits & Timeline
| Detail | Somerville, MA | Worcester, MA |
|---|
| Permit Timeline | Building-permit plan review typically 4-8 weeks — Confirm with Inspectional Services (617-625-6600 ext. 5600, isd@somervillema.gov) | 60-80 days |
| Permit Fees | Confirm with Inspectional Services — building permit fees are valuation-based; budget several thousand dollars on a typical $300K+ build | $2,800-$4,500 |
| Impact Fees | None for a single ADU — Confirm with Inspectional Services | $1,000-$1,800 |
| Pre-Approved Plans | None — Somerville does not offer a pre-approved AD | Not available |
Construction Costs
| Cost | Somerville, MA | Worcester, MA |
|---|
| Avg Build Cost | $275,000-$450,000 | $140,000-$280,000 |
| Cost Per Sq Ft | $400-$600 | $165-$330 |
| Garage Conversion | $150,000-$250,000 | $70,000-$160,000 |
| Prefab ADU | $180,000-$350,000 installed (site work, foundations, and buried utilities extra — confirm with manufacturer) | $110,000-$250,000 |
Rental Income Potential
| Rental | Somerville, MA | Worcester, MA |
|---|
| 1BR Avg Rent | $2,600-$3,000/mo | $1,250-$1,650/mo |
| 2BR Avg Rent | $3,300-$3,700/mo | $1,550-$2,150/mo |
| Short-Term Rentals | Effectively no — Somerville's STR ordinance (registration re | Not permitted |
| Est. ROI | 6-9% annual return | 7-10% annual return |
Which City Is Better for ADUs?
Somerville scores 7/10 while Worcester 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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