What Does It Actually Cost to Build an ADU in Denver Right Now
The gap between what homeowners expect to spend and what they actually spend is often $50,000 or more. Here are the hard numbers from completed Denver projects.
The gap between what homeowners expect to spend and what they actually spend is often $50,000 or more. Here are the hard numbers from completed Denver projects.
Building an accessory dwelling unit in Denver is not a $100,000 project anymore. It hasn’t been for years. Yet that figure—or something close to it—is what many homeowners carry when they start making calls to contractors. That gap is where projects stall, blow past budget, or die entirely.
The all-in cost for a 600-square-foot detached ADU in Denver right now runs $180,000 to $280,000, depending on your lot, your neighborhood, your soil, and what your contractor finds once the ground is open. That range comes from Denver-specific contractor data and the city’s own fee schedules—not national averages from ADU advocacy sites or contractor lead-gen pages that shade numbers low to collect your email address.
Three items routinely blindside owners who’ve done their homework: Denver Water tap fees, soft costs that never appear in a contractor’s bid, and the carrying costs that accumulate during what is realistically a 12-to-18-month process from decision to move-in. This piece works through each with actual numbers so you can build a budget that holds before you’ve spent a dollar.
Does Your Lot and Zone Actually Qualify?
Before any cost question matters, you need to know whether your property can legally have an ADU. Denver expanded allowances significantly through its 2021 zoning code updates, opening much of the city’s single-family residential land to accessory units by right. No public hearing. No special review. Just a building permit.
The relevant zone districts are U-SU-A, U-SU-B, U-SU-B1, U-SU-C, U-SU-C1, U-SU-E, and U-SU-G. In most of them, a detached ADU on an alley-loaded lot—or a garage or basement conversion—is permitted by right, provided your lot and proposed structure meet coverage limits, height limits, and setbacks in our home & property coverage. Where no alley exists or the lot configuration doesn’t accommodate a detached structure within those limits, you’re likely looking at interior conversions only.
Owner-occupancy requirements have shifted depending on what the city council has most recently decided, and that’s not a stable thing to assume you already know. Confirm the current status directly with Denver Community Planning and Development before proceeding—it affects whether a rental ADU can operate legally on your specific parcel.
Smaller lots create real physical constraints. In Cole, West Colfax, and Globeville, lots often run 25 to 33 feet wide, leaving very little room for a detached structure once setbacks are applied. Denver’s grid neighborhoods with rear alley access are a different story. Sunnyside, Park Hill, and Berkeley offer a practical advantage: a detached ADU or converted garage facing the alley tends to have fewer design complications and cleaner utility routing.
If your property is in Hilltop or you’re considering Cherry Hills Village, those jurisdictions fall outside Denver proper and operate under entirely different rules. Englewood, Lakewood, and Aurora each have their own ADU ordinances. This piece covers Denver city limits only.
Historic overlay districts add another layer. Denver has roughly 50 historic preservation overlay districts—Potter-Highlands, Curtis Park, and Whittier among the best known. In these areas, the exterior design, materials, and massing of any new structure require review by the Denver Landmark Preservation Commission. If your property is in or adjacent to one of these districts, that’s a timeline and design-cost factor to price in early. Don’t find this out after you’ve commissioned drawings.
Construction Cost Per Square Foot: Detached ADU vs. Garage Conversion vs. Basement
Detached new construction is the most expensive option. You’re building a complete stand-alone structure from scratch: foundation, framing, roof, all mechanical systems, all finishes. Contractors completing detached ADUs in Sunnyside, Park Hill, and Berkeley have reported all-in construction costs of $250 to $380 per square foot. For a 600-square-foot unit, that’s $150,000 to $228,000 in construction cost alone—before permits, before design fees, before your new Denver Water meter.
The spread within that range comes from finish level, foundation conditions, and mechanical system choices. A slab-on-grade unit with standard finishes and a simple rectangular footprint lands toward the lower end. A crawl space or full foundation, high-end kitchen and bath finishes, or a complex roofline moves you toward $350 or beyond. Custom window layouts, structural steel, or a geotechnical engineer’s special foundation design will push past $380.
Garage conversions look cheaper because the shell is already there. Total project costs have run $80,000 to $150,000. But that range assumes the existing structure is sound. Pre-1950s garages in Berkeley, West Highland, and Potter-Highlands frequently have poured concrete or rubble foundations that don’t meet current code for habitable space. That triggers remediation or a partial foundation rebuild. Add egress window cuts in masonry, HVAC rough-in, and insulation upgrades to meet Denver’s current energy code, and a conversion that looked like a $90,000 project becomes a $130,000 project before you’ve chosen tile.
Basement conversions offer the lowest entry point, typically $60,000 to $120,000, though variability here is high. The structure is already there. What you’re paying for is code-compliant egress, moisture management, HVAC extension or new systems, and finish work. The catch: older Denver homes often have basement ceiling heights that fall short of minimums for habitable space. If you’ve stood in a 1940s Park Hill basement, you know what I mean. A dig-down to lower the floor can add substantially to a project that initially looked like the affordable path. Some of the most successful basement conversions in the city have been in Park Hill and Berkeley, where homes tend to have deeper lots and better existing drainage than neighborhoods closer to downtown.
Soft Costs: The Line Items That Don’t Show Up in Contractor Bids
A contractor bid covers construction. It does not cover the costs that have to happen before construction starts, or that run alongside it. These soft costs are underestimated in almost every ADU planning budget I’ve seen.
Architectural and design fees typically run 8 to 15 percent of construction cost for a full-service architect. On a $180,000 construction project, that’s $14,400 to $27,000. Some Denver firms that specialize in ADUs offer flat-fee design packages—$8,000 to $20,000 for a complete permitted plan set—which can represent real savings on a straightforward project. One Park Hill architect who has completed twelve detached ADUs in the past five years charges a flat $12,000 for design through permit issuance. That’s become a useful reference point when homeowners are shopping around.
Structural engineering is not optional on a new detached ADU or a structural garage conversion. Budget $2,000 to $5,000 for a licensed structural engineer’s drawings and calculations. In neighborhoods with documented soil challenges, a structural engineer will specify foundation requirements that a general contractor would otherwise guess at. This is one of those fees that often pays for itself.
Soils reports matter specifically in Denver because of the city’s expansive bentonite clay. This soil swells when wet and shrinks when dry, and it has caused foundation problems across the Front Range for decades. In Globeville, Elyria-Swansea, and parts of Cole, a geotech report is something a careful contractor or structural engineer will require before specifying a foundation system. Budget $1,500 to $4,000. One Globeville homeowner spent $3,200 on a geotech report that identified a need for deeper footings—unglamorous, but it prevented a foundation failure.
A lot survey ($1,000 to $2,500) is typically required to confirm setbacks and property lines before CPD will approve your plans. West Highland lots, with their narrow frontages and irregular platting, often trigger survey complications that push costs toward the higher end.
Title and legal work applies if you’re financing through a home equity loan, refinance, or any product requiring a title company’s involvement. It won’t fit cleanly into anyone’s project estimate. It’s coming anyway.
Denver Water Tap Fees and Sewer Connection Costs
This is the line item that trips up even well-prepared homeowners. More than one contractor has called it the jaw-drop moment—and for good reason. It’s often the single biggest surprise on the budget sheet.
A new detached ADU in Denver typically requires its own Denver Water service tap, separate from the main house. Tap fees are based on meter size. For a ¾-inch meter—standard for a residential ADU—fees have run $8,000 to $13,000 or more. Confirm the current fee schedule directly at denverwater.org before budgeting, since these fees are subject to adjustment. A Sunnyside homeowner who pulled a permit in 2023 reported a tap fee of $11,400. A similar project in Park Hill a month earlier was quoted $8,800. That difference was driven by meter size and the location of the existing service connection—a good reminder that “similar project” doesn’t mean identical cost.
There’s an alternative worth investigating early. If your existing home’s meter has sufficient capacity to serve both the primary residence and the ADU, Denver Water may allow a shared service without a new tap. This requires a formal capacity review from Denver Water and isn’t guaranteed. But it can save $10,000 or more. Few homeowners ask about this option, and those who do sometimes find themselves cutting a five-figure cost out of the project entirely. Get this question on the table before you’ve finalized your project scope.
Sewer connection fees are separate from water. Denver Metro Wastewater Reclamation District—the relevant agency for most Denver addresses—charges connection fees that have run $4,000 to $8,000 depending on district and meter size. Your plumber should be able to tell you which district your address falls in and what the current rate is.
Taken together, water and sewer connection costs for a detached ADU can easily total $12,000 to $21,000 before any physical trenching or piping work. That single cost category routinely exceeds the total permit fees for the project. It needs its own line in your budget from day one.
Electrical and Gas Service Costs Through Xcel Energy
For a detached ADU, you’ll need to address electrical service as a separate structure. Xcel Energy serves most of Denver. Your ADU either gets its own service drop or is sub-metered from the main house’s existing service.
A separate service drop—Xcel running a new line from the nearest transformer—costs $2,000 to $6,000 depending on distance and whether any infrastructure upgrades are required on Xcel’s side. If your alley transformer is at capacity, which is not uncommon in older neighborhoods that are densifying, Xcel may require a transformer upgrade. That adds significant cost and delay of the type that doesn’t appear in any estimate until it’s already happening. Sub-metering, where the ADU shares the main service entrance but has a separate meter inside, is permissible in some configurations and can reduce costs. A Berkeley contractor reported that a sub-metered project saved one client roughly $3,000 in new service costs, though it required additional electrical design work to comply with code.
Gas service is increasingly optional in new ADU construction. Heat pump mini-splits, heat pump water heaters, induction cooktops—going all-electric eliminates the $1,000 to $4,000 cost of stubbing a new gas line to a detached structure and may qualify for utility incentives under Denver’s 2021 IECC energy code adoption. One Park Hill project that went all-electric qualified for a Xcel rebate that offset $1,800 of the heat pump installation cost. Not life-changing, but not nothing. If you haven’t yet decided on mechanical systems, run the all-electric question through your contractor and an energy consultant before locking in the design.
Confirm all Xcel fees and available incentives with Xcel’s residential new service department. The specifics depend on your address and load requirements, and figures change.
Denver CPD Permit Fees: How the Fee Schedule Works
Denver Community Planning and Development uses a valuation-based permit fee structure—a percentage of the declared construction valuation, scaling upward as project value increases. Not a flat fee.
For a project with a declared construction valuation of $150,000, the building permit fee runs roughly $1,500 to $3,000. Separate permits are required for mechanical, electrical, and plumbing work, each with its own fee—typically a few hundred dollars each at this project scale. A plan review fee, equal to approximately 65 percent of the building permit fee, is charged at plan submission, not at permit issuance. You’re paying a significant fee before you know whether your plans will be approved. Plan your cash flow accordingly.
The current fee schedule is published at denver.gov/permits. These numbers shift with each fiscal year, so verify against the live document rather than anything quoted online—including this article. It’s also worth asking CPD directly whether any ADU-specific fee waivers or reductions are currently available. Denver has explored fee incentives to encourage ADU production, and the status of any such programs is worth confirming before you submit.
How Long Does the Denver ADU Permit Process Actually Take?
Timeline management is as important as budget management. They’re connected: months of delays mean months of carrying costs on any construction financing you’ve taken out.
A pre-application conference with CPD is optional but worth doing—especially for projects on complicated lots, in historic overlay districts, or where zoning compliance isn’t entirely clear. Scheduling currently takes 2 to 4 weeks, costs nothing, and can save you a plan revision cycle that costs far more.
After design and engineering work is complete—4 to 8 weeks with most firms—you submit for permit and pay the plan review fee. Under current CPD conditions, standard ADU plan review runs approximately 6 to 14 weeks. That’s improved from 2021 and 2022, when backlogs stretched to six months. It’s still not fast. Projects requiring a Board of Adjustment variance or Landmark Preservation Commission design review add months to this phase. If your project is in a historic overlay district, budget an additional 4 to 8 months for the landmark review process alone, plus whatever design revisions result from commission feedback.
Once you have a permit, a standard detached ADU takes 4 to 8 months to build, depending on project complexity, the contractor’s schedule, and whether Denver’s weather cooperates during the foundation phase. Basement and garage conversions generally run 2 to 4 months.
Total elapsed time from decision to move-in for a detached ADU: 12 to 18 months is realistic. For a conversion, 8 to 12 months is more typical, assuming the permit process goes smoothly. Plan for the longer end of every range. You won’t be wrong.
Site-Specific Factors That Push the Number Up
The ranges above represent the middle of the market. Several factors push projects toward the top or beyond.
Expansive clay soils are the most common structural wildcard in Denver ADU construction. Denver’s bentonite clay swells when wet and shrinks when dry—responsible for foundation movement throughout the Front Range for decades. Globeville and Elyria-Swansea have documented soil challenges that can require deeper footings, moisture barriers, or engineered fill. One Elyria-Swansea homeowner paid an additional $8,000 in foundation costs after a geotech report identified conditions the contractor hadn’t anticipated. The report itself cost $3,000. Both were worth it.
Irregular or undersized lots in West Colfax and Sloan’s Lake can require significant architectural creativity to fit a legally compliant structure within setback and coverage limits. A West Colfax project that required a setback variance added three months to the permit timeline and $6,000 in additional design and legal work.
Winter construction starts add roughly 5 to 10 percent to foundation costs. Ground frost and concrete curing temperature requirements mean insulated formwork, heated enclosures, or accelerated mixes. If your permit comes through in November, factor this in. A lot of homeowners don’t, and they’re surprised when the contractor invoice reflects it.
Hail-resistant roofing is a practical consideration in the Denver metro, which consistently ranks among the most hail-active markets in the country. Specifying a Class 4 impact-resistant product on an ADU adds modest upfront cost and can meaningfully affect insurance premiums. Ask your contractor about this specifically—it’s rarely raised unless you bring it up, which is strange given how often Denver gets hammered in late spring.
How to Use This Information Before You Call a Contractor
The sequence matters as much as the numbers.
Start at the zoning map. Denver’s online zoning map, accessible through the city’s My Neighborhood portal, will show your zone district and whether an ADU is permitted by right. Do this before spending any money. It takes twenty minutes.
Request a pre-application conference with CPD once you have a general sense of what you want to build. It’s free and will surface site-specific requirements before you’ve paid for design work.
Contact Denver Water early for a service capacity determination. Ask specifically whether your existing meter can serve the ADU without a new tap. This single question can save you $10,000 or more, and most homeowners never ask it.
When you solicit contractor bids, ask for an itemized estimate that separates construction cost from soft costs and utility connection fees. A bid that lumps everything together is a bid you can’t evaluate. Ask each contractor what their most recent comparable Denver ADU cost, where it was built, and what drove the final number. If they can’t answer specifically, that tells you something.
Ask CPD whether pre-approved ADU plan sets are available. Denver has explored standard plan programs—pre-reviewed designs that can be purchased and used as-is, reducing design fees and potentially shortening plan review time. Confirm directly with CPD before commissioning custom drawings.
On financing: CHFA programs and local credit unions that have developed ADU-specific loan structures are worth investigating early, because the financing structure affects your carrying costs throughout the permit and construction period. One Berkeley homeowner secured a home equity line of credit structured to disburse in phases matching her construction timeline—she only paid interest on money actually drawn during the 14-month project. That’s the kind of structure worth asking about specifically, rather than taking whatever product a lender leads with.
An ADU in Denver is a capital project, not a home improvement. The homeowners who get through it on budget are the ones who priced permits, soft costs, utility connections, and timeline before the contractor invoices started arriving—not after.
