ADU Costs in Somerville, MA
Estimate ADU costs in Somerville, Massachusetts based on local size limits, allowed types, and zoning rules. Plan your budget with real data.
ADU Regulations in Somerville
Somerville follows the Massachusetts state baseline under the Affordable Homes Act. This means all Massachusetts state-level ADU rights apply — including by-right approval, no owner occupancy requirement, and standardized size limits. Somerville may also have additional local regulations that supplement the state baseline.
Cost by ADU Type in Somerville
Interior conversions are the most affordable option at $100-$200 per square foot, since you're reusing existing structure. Attached ADUs typically cost $150-$250 per square foot, sharing a wall and utility connections with your existing home. Detached ADUs are the most expensive at $200-$350 per square foot, but offer the most privacy and design flexibility.
Budget for a Full-Size ADU
With 900 sq ft allowed in Somerville, a maximum-size detached ADU could cost $180k-$315k for construction alone. Add 15-25% for permits, design, site work, and utility connections. A smaller footprint can significantly reduce costs.
Return on Investment
ADUs in Somerville can generate significant rental income while also increasing your property value. With a population of 81,360, Somerville has strong rental demand that supports competitive rates. Without owner occupancy requirements, you have full flexibility to maximize your rental returns — including the option to rent both units.
Somerville ADU Rules at a Glance
Max Size
900 sq ft
% of Home
50%
Max Height
25 ft
Max Stories
2
Front Setback
10 ft
Side Setback
3 ft
Rear Setback
3 ft
Parking
None required
Approval
BY RIGHT
Owner Occupancy
Not required
Rental Allowed
Yes
Short-Term Rental
Not allowed
Somerville Building Department
Frequently Asked Questions
How much does it cost to build an ADU in Somerville, MA?
ADU costs in Somerville typically range from $150,000 to $350,000+ depending on the type. With a maximum size of 900 sq ft allowed, a full detached ADU (the most expensive option) in Somerville could cost $200-$350/sq ft. Interior conversions are typically the most affordable at $100-$200/sq ft.
What is the cheapest type of ADU to build in Somerville?
In Somerville, a conversion ADU is typically the most affordable option. Interior conversions reuse your existing structure (basement, attic, or garage), eliminating foundation and framing costs. Somerville allows detached, attached, conversion ADUs, giving you flexibility to choose based on your budget.
Are there ADU financing options in Somerville?
Common ADU financing options available to Somerville homeowners include home equity loans (HELOCs), construction loans, cash-out refinancing, and renovation loans (FHA 203k or Fannie Mae HomeStyle). Some Massachusetts programs also offer ADU-specific financing or incentives.
What rental income can I expect from an ADU in Somerville?
ADU rental income in Somerville depends on size, finishes, and location. A full 900 sq ft unit (2-bedroom) can command premium rents. With a population of 81,360, Somerville has strong rental demand that supports competitive rates.
Do ADU permit fees add significantly to costs in Somerville?
Permit fees in Somerville typically range from $1,000 to $5,000 depending on the project scope. While not the biggest cost factor, budget for building permits, plan review fees, utility connection fees, and any impact fees. By-right approval in Somerville means you avoid the additional costs of hiring a lawyer for public hearings.
Where can I find all ADU regulations for Somerville?
Visit our complete ADU rules page for Somerville, MA for a full overview of zoning, permits, size limits, setbacks, parking, and costs. We cover all Massachusetts municipalities with data sourced from local ordinances and state law.
Check Your Address
See exactly what ADU rules apply to your specific property in Somerville.