An ADU builder in Detroit 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 Detroit's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Michigan.
What ADU Builders Cost in Detroit [6][7]
Based on our Detroit 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) | $90,000-$200,000 |
| Cost per Sq Ft | $140-$240 |
| Garage Conversion | $45,000-$100,000 |
| Prefab / Modular ADU (installed) | $75,000-$150,000 |
| City Permit & Plan Review | Building permit fees based on construction value — confirm with Detroit BSEED once ADU rules take effect |
| Impact Fees | None — Michigan law does not authorize municipal development impact fees; budget for water/sewer connection charges via DWSD |
For a full line-item breakdown, see our Detroit ADU cost guide. To confirm what you're allowed to build before you hire, review the Detroit ADU rules (max detached size: Proposed: no more than the smaller of 1,200 sq ft or 60% of the principal dwelling's gross floor area (Sec. 50-12-466); not yet in effect; owner-occupancy: No owner-occupancy requirement appears in the proposed ordinance text — confirm final adopted language with the City Planning Commission).
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How to Vet an ADU Builder in Detroit
- License: Confirm a current contractor's license in Michigan 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 Detroit 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 (Building permit fees based on construction value — confirm with Detroit BSEED once ADU rules take effect), plan check (Would follow standard BSEED plan review; the proposed ordinance requires ADUs to contain complete independent living facilities (sleeping, cooking, eating, sanitation)), and impact fees (None — Michigan law does not authorize municipal development impact fees; budget for water/sewer connection charges via DWSD) are included.
- Permit handling: Confirm they manage Detroit's permit process ("No standard ADU permitting pathway exists yet — ADUs are barred in R1/R2 under current code and need special approvals elsewhere. If the amendment is adopted, ADUs in R2-R6 would be by right through a Buildings, Safety Engineering and Environmental Department (BSEED) building permit. Confirm current status with BSEED and the City Planning Commission (313-224-6225)", typically Not applicable until the ordinance is adopted — City Council was still deliberating as of spring 2026) 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 Detroit 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 (Not applicable until the ordinance is adopted — City Council was still deliberating as of spring 2026) 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 Michigan ADU client references?
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