Zoning & Size Limits
| Requirement | Cambridge, MA | Boston, MA |
|---|
| Allowed Zones | Residential zones R-1 through R-4 | Select residential zones |
| Max Size (Detached) | 950 sq ft | 900 sq ft or 50% of living area (whichever is less) |
| Max Size (Attached) | 850 sq ft | 900 sq ft or 50% of living area (whichever is less) |
| Max Height | 35 feet | 35 feet |
| Parking Required | Optional | 1 space per unit |
| Owner Occupancy | Not required | May be required in some zones |
Setback Requirements
| Setback | Cambridge, MA | Boston, MA |
|---|
| Rear Setback | 15 feet | 20 feet |
| Side Setback | 3 feet | 5 feet |
| Front Setback | 15 feet | 20 feet |
Permits & Timeline
| Detail | Cambridge, MA | Boston, MA |
|---|
| Permit Timeline | 60-90 days | 90-150 days |
| Permit Fees | $3,500-$5,500 | $4,500-$7,500 |
| Impact Fees | $1,500-$2,500 | $2,000-$3,500 |
| Pre-Approved Plans | Not available | Not available |
Construction Costs
| Cost | Cambridge, MA | Boston, MA |
|---|
| Avg Build Cost | $210,000-$420,000 | $200,000-$400,000 |
| Cost Per Sq Ft | $220-$440 | $220-$440 |
| Garage Conversion | $105,000-$230,000 | $100,000-$220,000 |
| Prefab ADU | $160,000-$340,000 | $150,000-$320,000 |
Rental Income Potential
| Rental | Cambridge, MA | Boston, MA |
|---|
| 1BR Avg Rent | $1,900-$2,500/mo | $1,800-$2,400/mo |
| 2BR Avg Rent | $2,300-$3,400/mo | $2,200-$3,200/mo |
| Short-Term Rentals | Not permitted | Not permitted |
| Est. ROI | 5-7% annual return | 5-7% annual return |
Which City Is Better for ADUs?
Cambridge scores 7/10 while Boston scores 6/10 on our ADU-friendliness index.
Cambridge 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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