How Much Does an ADU Cost in Denver Metro, Colorado?

Building an accessory dwelling unit is a significant investment, and understanding the full cost picture before you commit is essential. ADU pricing in the Denver Metro area depends on the type of unit, its size, the quality of finishes you choose, site conditions on your property, and the cost of permits and utility connections.

This guide breaks down costs by ADU type, explains the major cost drivers, and gives you realistic ranges based on current construction pricing in the south Denver metro area.

ADU Cost by Type

The most important factor in your ADU budget is which type of unit you build. Here is what each option typically costs in the Denver Metro area.

ADU Type	Cost Range	Cost Per Sq Ft	Typical Size
Detached Backyard Cottage	$200,000 – $400,000	$250 – $500	500 – 800 sq ft
Above-Garage ADU	$120,000 – $300,000	$200 – $500	400 – 600 sq ft
Garage Conversion	$50,000 – $150,000	$100 – $250	400 – 600 sq ft
Basement Conversion	$40,000 – $120,000	$80 – $200	500 – 1,000 sq ft

Detached Backyard Cottage: $200,000 – $400,000

A detached ADU is a brand-new standalone structure built from the ground up in your backyard. It requires a new foundation, new utility connections (water, sewer, electrical, gas), and full construction from framing through finishes. This is why it carries the highest price tag — but it also delivers the most value in terms of rental income, property value increase, and design flexibility.

The wide cost range reflects the difference between a basic 500 square foot studio with standard finishes and a fully custom 800 square foot two-bedroom unit with premium fixtures, custom cabinetry, and high-end appliances. Most Denver Metro homeowners building a detached ADU land somewhere in the $250,000 to $350,000 range.

Garage Conversion: $50,000 – $150,000

Converting an existing garage is significantly less expensive than new construction because the structural shell — walls, roof, and foundation — already exists. Your primary costs are interior buildout: insulation, drywall, flooring, plumbing, electrical, HVAC, a kitchen, and a bathroom. The lower end of the range covers a basic conversion of a single-car garage with modest finishes. The upper end reflects a full two-car garage transformation with separate bedroom, full kitchen, upgraded finishes, and new utility runs.

Basement Conversion: $40,000 – $120,000

If your home has a walkout basement — common in Denver Metro due to the rolling terrain — a basement ADU conversion is often the most affordable path. The space is already enclosed and climate-controlled in most cases. Key costs include adding a separate entrance (required for a legal ADU), installing or upgrading a kitchen and bathroom, meeting egress window requirements, addressing radon mitigation (required in Colorado), and adding sound insulation between the basement unit and the main home above.

What Drives ADU Costs Up or Down

Site Conditions

Every lot is different. If your backyard has steep slopes requiring grading or retaining walls, costs rise. If utility connections need to run a long distance from the street or main house, trenching and connection fees add up. Properties with mature trees, difficult access for construction equipment, or challenging soil conditions can add $10,000 to $50,000 to a detached ADU project.

Finishes and Fixtures

Standard builder-grade finishes (laminate countertops, vinyl plank flooring, basic cabinetry) sit at the lower end of the range. Upgraded finishes (quartz countertops, hardwood or tile flooring, custom cabinets, premium appliances) push costs toward the upper end. This is one area where you have the most control over your budget.

Permits and Fees

Permit fees in the Denver metro area typically range from $3,000 to $15,000 depending on the jurisdiction and project scope. Utility connection fees — especially water tap fees for a new detached ADU — can add $5,000 to $20,000 or more. Denver Water, for example, requires a separate water supply license for ADUs, plus a system development charge. These fees are not optional and should be factored into your budget from the start.

Size

Smaller ADUs have a higher cost per square foot than larger ones because certain fixed costs — kitchen, bathroom, mechanical systems, utility connections, permits — exist regardless of size. A 500 square foot ADU might cost $300 per square foot, while an 800 square foot unit could come in at $250 per square foot. But the total cost of the larger unit is still higher. Choose the size that fits your goals and budget, not just the lowest per-square-foot number.

ADU Financing Options

Most homeowners finance their ADU through one of these methods:

• Home Equity Line of Credit (HELOC): Borrow against your existing home equity. Often the simplest option for homeowners with significant equity. Interest rates are variable.
• Cash-Out Refinance: Refinance your mortgage for a higher amount and use the difference for construction. Works best when current interest rates are favorable.
• Construction Loan: A short-term loan specifically for the build phase, which converts to a permanent mortgage upon completion. Requires more paperwork but designed for new construction.
• Colorado ADU Grant Program: The state allocated $8 million in funds for low- and moderate-income homeowners to build ADUs. Check the Colorado Division of Local Affairs for current availability and eligibility.

Will an ADU Increase My Property Value?

ADUs generally increase property value by 20 to 35 percent, according to industry estimates across markets with established ADU programs. The value increase depends on the type of ADU, its quality, and local market conditions. A well-built detached ADU with a full kitchen and bathroom is the most valuable addition, as it represents a fully independent living unit that future buyers can use for rental income, family housing, or as flexible space.

In the Denver Metro market, where the average home already commands nearly $580,000, even a conservative 20 percent increase from a quality ADU represents over $100,000 in added equity — often more than half the cost of the unit itself.