How Much Does an ADU Cost in Denver? (2026 Guide)

The ADU cost Denver homeowners should plan for depends mostly on the type of unit you build. A new ADU can cost more than $300,000 to build, according to Denverite. Units built through the city-supported West Denver Single Family Plus (WDSF+) ADU pilot ranged from about $213,000 for a studio to $322,000 for a larger unit, Westword reported in 2023. Garage conversions usually cost less because they reuse an existing structure. Utility connections, unit size, soil conditions, and finish level cause the biggest swings from one project to the next.

ADU Cost Denver Homeowners Can Expect by Type

Every lot is different, so treat the figures below as planning context, not bids.

Garage Conversion

• Usually the lowest-cost path, because the foundation, walls, and roof already exist
• The budget goes to insulation, plumbing, electrical, heating and cooling, and finishes
• Costs climb if the slab or framing needs structural work, or if utilities must be run from the main house

Attached ADU

• Built onto the side or rear of the main house, or created inside existing space such as a basement or attic
• Can often share water, sewer, and electric service with the main house
• An addition requires tying into the existing roof, foundation, and structure

Detached Backyard ADU

• In the WDSF+ pilot, small one- and two-bedroom units cost $243,000 to $290,000, and large two- and three-bedroom units cost $270,000 to $322,000, per Westword
• Westword also reported that the program saved participants an average of $50,000 to $75,000 compared with market-rate ADU construction, so a typical market-rate project can cost more
• Needs a new foundation, framing, roof, and its own utility connections

Hammer Hero designs, permits, and builds ADUs in Denver, including detached backyard units, above-garage units, and attached additions.

What Drives ADU Cost in Denver?

Several factors move ADU cost Denver projects up or down:

• Utility connections. Denver Water charges a one-time System Development Charge of $2,170 for a detached ADU inside Denver, rising to $2,260 on January 1, 2027, according to its current fee schedule. If the property’s water service line is not copper, Denver Water requires replacing it from the main to the first copper or brass fitting. Sewer and electric work add more, and long runs from existing service cost the most.
• Materials and labor. In a UC Berkeley Terner Center study of ADUs in Portland, Seattle, and Vancouver, construction labor (33%) and materials (34%) were the two biggest cost components. Your finish choices move this number more than anything else.
• Foundation and soil. The Colorado Geological Survey calls expansive, swelling clay soil Colorado’s most significant geologic hazard, so plan for a soils report and a foundation designed for your lot.
• Design complexity and finishes. A simple footprint with standard windows costs far less than a custom layout with high-end cabinetry.
• Permits and engineering. In the same Terner Center study, architecture and engineering made up about 8% of project costs and city permits about 8%. Utility connections added about 5%.

What Permits Does an ADU Need in Denver?

According to the City and County of Denver, a new ADU needs zoning, building, and sewer use and drainage permits, plus trade permits for electrical, plumbing, and mechanical work. A licensed contractor must pull these permits, because homeowners cannot apply for them. The ADU also needs a Certificate of Occupancy before anyone can live in it.

In single unit zone districts, the owner must live in the main house when applying for ADU permits. ADUs in historic districts need a certificate of appropriateness first. See the city’s page on permitting an ADU in Denver for current requirements.

Is a Garage Conversion Cheaper Than a New Detached ADU?

In most cases, yes. A garage conversion reuses an existing foundation, walls, and roof, which is why it usually costs well below new construction. The savings shrink if the garage needs a new slab, major framing repairs, or a long utility run.

Weighing an ADU against building onto the main house? Our comparison of ADU vs. home addition breaks down the tradeoffs. Starting with a garage? Read whether a garage conversion to ADU is right for your property.

How Can You Keep ADU Costs Down?

• Convert a sound existing garage instead of building from scratch when your lot allows it.
• Place the ADU close to existing water, sewer, and electric lines.
• Choose a simple footprint and standard window and door sizes.
• Finalize the design before permit submission, since changes after approval cost time and money.
• Ask for itemized bids that separate utilities, permits, and construction.
• Check local programs. Denverite reports that the WDSF+ ADU pilot offers pre-designed floorplans and financial assistance for some homeowners.

Want ADU cost Denver numbers for your specific lot? Get a free ADU estimate from the Hammer Hero team.

Frequently Asked Questions