ADU Cost Estimator for Massachusetts
How much does an ADU cost in Massachusetts? Get a preliminary planning range for a detached ADU, attached ADU, garage conversion, or basement ADU, based on fixed Massachusetts market assumptions — not a quote and not site-specific.
Plan Your Budget
Answer a few quick questions for a preliminary planning range based on fixed Massachusetts market assumptions. It is not a quote, not site-specific, and not our detailed internal estimate — no commitment required.
What size ADU are you considering?
Select the approximate living space you have in mind.
ADU Cost Questions — Massachusetts
How much does an ADU cost in Massachusetts?
There is no single ADU price for Massachusetts. Final cost varies by site, utilities, foundation, selections, current trade bids, the builder's fee, and owner-controlled contingency. This estimator gives a preliminary construction planning range from fixed market assumptions — it is not a quote and not site-specific. Design, engineering, permitting, utilities, site conditions, selections, and current trade bids can change the result materially.
How much does a 900 sq ft ADU cost in Massachusetts?
This estimator is focused on the 900 sq ft statutory maximum prototype, which is why 900 sq ft is the largest option here. Massachusetts caps a protected single-family accessory dwelling unit at 900 sq ft, and local rules plus the 50%-of-primary-dwelling limitation can reduce that further on your lot — so a larger ADU should not be assumed. Final price for a 900 sq ft detached ADU varies by site, utilities, foundation, selections, current bids, fee, and contingency. The estimator's range is a preliminary planning figure from fixed market assumptions, not a quote and not site-specific.
How much does a garage conversion ADU cost?
Garage conversion ADUs are usually the most cost-effective path, often 20–35% cheaper than a comparable detached build because the shell already exists. Final cost depends on foundation upgrades, utilities, and code-required insulation and egress.
Is this estimate a real quote?
No — it is a preliminary planning range based on fixed Massachusetts market assumptions. It is not site-specific and it is not our detailed internal estimate. A firm quote requires a site walk and a preliminary plan set, which we handle as part of our design-build process.