An ADU builder in Cambridge is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Cambridge's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Massachusetts.
What ADU Builders Cost in Cambridge [3][4]
Based on our Cambridge cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $210,000-$420,000 |
| Cost per Sq Ft | $220-$440 |
| Garage Conversion | $105,000-$230,000 |
| Prefab / Modular ADU (installed) | $160,000-$340,000 |
| City Permit & Plan Review | $3,500-$5,500 |
| Impact Fees | $1,500-$2,500 |
For a full line-item breakdown, see our Cambridge ADU cost guide. To confirm what you're allowed to build before you hire, review the Cambridge ADU rules (max detached size: 900 sq ft or 50% of primary dwelling, whichever is less (MA state by-right cap); owner-occupancy: Not required (prohibited under MA Affordable Homes Act / 760 CMR 71)).
Get Free ADU Quotes in Cambridge
We forward your request to licensed ADU contractors serving your area. Free, no obligation.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
How to Vet an ADU Builder in Cambridge
- License: Confirm a current contractor's license in Massachusetts and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Cambridge and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits ($3,500-$5,500), plan check (3-4 weeks), and impact fees ($1,500-$2,500) are included.
- Permit handling: Confirm they manage Cambridge's permit process ("Building permit with design review", typically 60-90 days) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Cambridge in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (60-90 days) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Massachusetts ADU client references?
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
Some links on this page are affiliate links. We may earn a commission at no extra cost to you. Learn more
Are you an ADU builder? Get Cambridge leads
Homeowners on this page submit real ADU project requests in Cambridge. We match each one to a local builder. Your first lead is free, then a small per-lead fee — no subscription, and you contract directly with the homeowner.
Get Cambridge ADU Leads →Frequently Asked Questions
How much do ADU builders charge in Cambridge?
How do I find a good ADU builder in Cambridge?
Do ADU builders in Cambridge handle permits?
How long does it take to build an ADU in Cambridge?
Get Free ADU Builder Quotes in Cambridge
Compare bids from pre-screened, licensed Cambridge ADU builders. Free, no obligation.
Get Free Quotes →