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 [15][16][17]
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) | $200,000-$450,000 |
| Cost per Sq Ft | $250-$500 |
| Garage Conversion | $80,000-$150,000 |
| Prefab / Modular ADU (installed) | $175,000-$425,000 |
| City Permit & Plan Review | Building permit is valuation-based: $770 + $5.60 per $1,000 over $100,000 (about $1,330 at $200,000) plus a 50% plan-review fee; zoning permit $150 + $0.50 per $1,000; SUDP $425 application + $150 inspection; Denver Water ADU system development charge $2,170 (from Jul 1, 2026). |
| Impact Fees | Denver has no development impact fee, and ADUs are an exception to the affordable-housing linkage fee (DRMC 27-154; documented at building permit). Denver Water ADU SDC $2,170 inside Denver; a sanitary connection fee applies only if the ADU gets its own water service instead of sharing the house's. |
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: SU districts: ADU gross floor area 864 sq ft on lots of 7,000 sq ft or less, 1,000 sq ft on larger lots (DZC 11.8.2.1.B.2); the detached ADU building footprint is capped at the same 864/1,000 sq ft (e.g., DZC 5.3.4.5.A). Other districts: 1,000 sq ft footprint per unit, GFA not separately capped.; owner-occupancy: Only at the time of permit application, and only in single-unit (SU) districts: an owner must live in the existing house as their primary residence (shown by two of driver's licence, vehicle or voter registration, tax documents, utility bill). Waived when house and ADU are built together; no ongoing requirement (DZC 11.8.2.2.B, per CB24-1303 and C.R.S. 29-35-103(2)(b)). ADU and house must stay under one ownership (11.8.2.2.A).).
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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 (Building permit is valuation-based: $770 + $5.60 per $1,000 over $100,000 (about $1,330 at $200,000) plus a 50% plan-review fee; zoning permit $150 + $0.50 per $1,000; SUDP $425 application + $150 inspection; Denver Water ADU system development charge $2,170 (from Jul 1, 2026).), plan check (Zoning, building and SUDP reviews run concurrently when all required documents are uploaded with the initial application; a property survey is needed if building within 3 ft of a lot line. New construction over 500 sq ft also needs an approved URCO waste-diversion plan and refundable deposit before the permit issues.), and impact fees (Denver has no development impact fee, and ADUs are an exception to the affordable-housing linkage fee (DRMC 27-154; documented at building permit). Denver Water ADU SDC $2,170 inside Denver; a sanitary connection fee applies only if the ADU gets its own water service instead of sharing the house's.) are included.
- Permit handling: Confirm they manage Denver's permit process ("Administrative, no hearing: zoning, building and sewer use & drainage (SUDP) permits are filed together in Denver e-permits (scope 'New Accessory Dwelling Unit') for simultaneous review. A licensed contractor must apply; homeowners cannot pull ADU permits. Landmark or historic-district properties need a certificate of appropriateness first.", typically Not published as a fixed figure: Denver's Average Plan Review Times dashboard (updated daily) shows current 'Major Residential' review times. Trade permits for new construction need the issued residential construction permit first (since May 22, 2025).) 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 (Not published as a fixed figure: Denver's Average Plan Review Times dashboard (updated daily) shows current 'Major Residential' review times. Trade permits for new construction need the issued residential construction permit first (since May 22, 2025).) 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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