As of October 2026, Block Renovation's 2026 cost analysis puts a detached ADU in Denver at about $230,000 to $310,000 and says garage conversions start around $140,000. It also puts Colorado all-in costs at roughly $200 to $300 per square foot. Your lot, utilities and finishes decide where a project lands.
What do published figures say by ADU type?
| ADU type | Published figure, as of October 2026 | Scope |
|---|---|---|
| Detached ADU | About $230,000 to $310,000 | Denver-specific |
| Garage conversion | From about $140,000 | Denver-specific |
| Attached ADU | About $100,000 to $250,000 | National |
| Basement ADU | About $50,000 to $120,000 | National |
All figures come from one source, Block Renovation's 2026 analysis. They are published estimates, not our prices. National numbers blend cheaper and costlier regions, so treat them as a rough frame for Denver.
What costs sit on top of construction?
- Design and engineering. The same analysis puts these at about 10% to 15% of construction cost.
- Permit and impact fees. Published at about $1,500 to $25,000 nationally, depending on the city and project. Colorado's HB24-1152 still lets cities charge generally applicable impact fees on ADUs.
- Water service. Denver Water may require a new license for the ADU's water service, with possible fees.
- Sewer and electrical. Trenching to the sewer main and upgrading an older electrical service.
- Demolition. Removing an old garage or shed needs its own permit.
Why do Denver ADU quotes vary so much?
It depends on what each quote leaves out. One may cover only the building; another may include drawings, engineering, permits, utility tie-ins and the certificate of occupancy. Ask every builder for a written, itemized quote and compare line by line, especially allowances for finishes and how unknowns underground are handled.
What pushes a Denver ADU's price up or down?
- Type. Building inside existing space usually costs less than new construction.
- Neighborhood context. A two-story ADU in an urban context needs more structure than a one-story suburban unit.
- Alley access. An alley shortens the path for crews, materials and sometimes utilities.
- Historic review. Landmark districts can add design work and time.
- Finishes. Cabinets, flooring and fixtures can move the total either way.
Is there help paying for an ADU in Colorado?
Possibly. The Department of Local Affairs runs an ADU grant program for local governments, which can fund things like fee reductions and pre-approved plans in certified ADU-supportive jurisdictions. Homeowners in those jurisdictions can also work with lenders on CHFA ADU finance programs. Availability depends on your city.
Sources, as of October 2026:
- Block Renovation, “A Deep Dive Into ADU Construction Costs” (April 2026, updated June 2026), for cost ranges and soft-cost estimates.
- Colorado Department of Local Affairs, Accessory Dwelling Units page, for HB24-1152, impact fees, grants and CHFA programs.
- City and County of Denver, Permitting an Accessory Dwelling Unit, for Denver Water and demolition permits.