An ADU builder in Denver 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 Denver's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Colorado.
What ADU Builders Cost in Denver [4][5]
Based on our Denver 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) | $140,000-$280,000 |
| Cost per Sq Ft | $130-$260 |
| Garage Conversion | $70,000-$160,000 |
| Prefab / Modular ADU (installed) | $100,000-$230,000 |
| City Permit & Plan Review | $500-$5,000 building permit + $2,055-$3,030 Denver Water SDC; total permit/utility typically $7K-$13K |
| Impact Fees | Denver Water system development charge applies; see fees |
For a full line-item breakdown, see our Denver ADU cost guide. To confirm what you're allowed to build before you hire, review the Denver ADU rules (max detached size: Up to 1,000 sq ft on lots over 7,000 sq ft (864 sq ft on 6,000-7,000 sq ft lots; ~650 sq ft on smaller lots) — varies by zone district; owner-occupancy: Not required (removed by CB24-1303, effective Dec 16, 2024; consistent with CO HB24-1152)).
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How to Vet an ADU Builder in Denver
- License: Confirm a current contractor's license in Colorado 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 Denver 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 ($500-$5,000 building permit + $2,055-$3,030 Denver Water SDC; total permit/utility typically $7K-$13K), plan check (Several weeks to a few months depending on backlog), and impact fees (Denver Water system development charge applies; see fees) are included.
- Permit handling: Confirm they manage Denver's permit process ("Administrative (by-right) approval — no public hearing", typically 4-7 months realistic from application to issued permit (zoning + building review)) 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 Denver 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 (4-7 months realistic from application to issued permit (zoning + building review)) 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 Colorado ADU client references?
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Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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