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 [9][10]
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 | BSEED building permit (fee schedule modified 7/18/2025): $2,895.29 at $100,000 project cost plus $27.82 per $1,000 above that (about $4,286 at $150,000); trade permits and a 35% plan-review deposit are extra. Relevant only if the zoning changes. |
| Impact Fees | None: the BSEED fee schedule lists no development impact or capacity fee. Budget instead for DWSD water and sewer connection charges if a separate service is ever needed. |
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: No ADU size rule exists because no ADU use exists. The lapsed proposal (draft Sec. 50-12-466(1)e) would have capped an ADU at the smaller of 1,200 sq ft or 60% of the principal dwelling's gross floor area. Today a building accessory to a one- or two-family house is limited to one story and 15 ft (Sec. 50-13-209).; owner-occupancy: None in the code (no ADU use exists) and none in the lapsed proposal's text.).
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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 (BSEED building permit (fee schedule modified 7/18/2025): $2,895.29 at $100,000 project cost plus $27.82 per $1,000 above that (about $4,286 at $150,000); trade permits and a 35% plan-review deposit are extra. Relevant only if the zoning changes.), plan check (Building, structural and zoning plan review is taken as a 35% deposit against the building permit fee, with electrical, mechanical and plumbing plan review at 7% each (BSEED fee schedule Part F); a self-contained unit would need all four.), and impact fees (None: the BSEED fee schedule lists no development impact or capacity fee. Budget instead for DWSD water and sewer connection charges if a separate service is ever needed.) are included.
- Permit handling: Confirm they manage Detroit's permit process ("No ADU permit path exists because the use is not allowed: BSEED cannot issue a building permit for a dwelling unit in an accessory building in R1 or R2 (Sec. 50-12-454(a)), and no special-approval route for one is published. Ask BSEED Zoning for a zoning verification letter ($93 per address) if you are told otherwise, and watch the City Planning Commission's ordinance page for any revived text.", typically Not applicable: no ADU permit can be issued under current zoning, and as of September 2026 no ADU ordinance is before City Council.) 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: no ADU permit can be issued under current zoning, and as of September 2026 no ADU ordinance is before City Council.) 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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