Zoning & Size Limits
| Requirement | Boston, MA | New York City, NY |
|---|
| Allowed Zones | Interior ADUs as-of-right in owner-occupied 1-3 family homes | R1-R5 residential zones (NOT R1A, R2A, R3A unless in Greater |
| Max Size (Detached) | Not as-of-right — ZBA variance required (by-right only in Mattapan) | Up to 800 sq ft (and no more than 33% of the required rear yard) where permitted under City of Yes; not allowed in historic districts or R1A/R2A/R3A zones outside the Greater Transit Zone |
| Max Size (Attached) | Not as-of-right — ZBA variance required (by-right only in Mattapan) | 800 sq ft |
| Max Height | 35 feet | 15 ft (detached, zero lot line, or semi-detached A |
| Parking Required | None required for an interior ADU | Not required |
| Owner Occupancy | Required (owner-occupied 1-3 family home; condos and LLCs in | Owner must occupy either the primary home or the ADU |
Setback Requirements
| Setback | Boston, MA | New York City, NY |
|---|
| Rear Setback | 20 feet (applies to variance/Mattapan detached units) | N/A |
| Side Setback | 5 feet (applies to variance/Mattapan detached units) | N/A |
| Front Setback | 20 feet (applies to variance/Mattapan detached uni | N/A |
Permits & Timeline
| Detail | Boston, MA | New York City, NY |
|---|
| Permit Timeline | 90-150 days | 120-180 days |
| Permit Fees | $4,500-$7,500 | $5,000-$10,000 |
| Impact Fees | $2,000-$3,500 | Varies by borough |
| Pre-Approved Plans | Not available | Yes — DOB/HPD Pre-Approved ADU Plan Library launch |
Construction Costs
| Cost | Boston, MA | New York City, NY |
|---|
| Avg Build Cost | $200,000-$400,000 | $150,000-$300,000 |
| Cost Per Sq Ft | $220-$440 | $300-$600 |
| Garage Conversion | $100,000-$220,000 | $120,000-$260,000 |
| Prefab ADU | $150,000-$320,000 | Rarely feasible (site access/crane limits) |
Rental Income Potential
| Rental | Boston, MA | New York City, NY |
|---|
| 1BR Avg Rent | $1,800-$2,400/mo | $2,200-$3,200/mo |
| 2BR Avg Rent | $2,200-$3,200/mo | $2,800-$4,200/mo |
| Short-Term Rentals | Not permitted | Heavily restricted (primary unit rule) |
| Est. ROI | 5-7% annual return | 4-6% annual return |
Which City Is Better for ADUs?
Boston scores 5/10 while New York City scores 5/10 on our ADU-friendliness index.
Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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