Types of Accessory Dwelling Units You Can Build in Denver
A detailed look at all four ADU types — pros, cons, costs, and which one fits your property.
Detached Backyard ADU
A detached ADU is a completely separate structure built in your backyard — a standalone home with its own entrance, kitchen, bathroom, and living space. This is the most popular ADU type for rental income because it offers maximum privacy for both you and your tenant.
TYPICAL COST
$180,000 – $350,000
SIZE RANGE
400 – 1,200 sq ft
TIMELINE
4–6 months construction
Advantages
- Highest rental income potential
- Maximum privacy for homeowner and tenant
- Most flexible design options
- Strongest property value increase
- Can include garage or carport
Considerations
- Highest construction cost
- Requires sufficient yard space
- Utility connections can be expensive
- Longest construction timeline
Ideal For
Homeowners with larger lots who want to maximize rental income or create a fully independent living space for family members. Most popular in Denver, Wheat Ridge, Arvada, Lakewood, and Littleton.
Permit Requirements
Requires full building permit including foundation, structural, electrical, plumbing, and mechanical inspections. Most Denver metro cities process detached ADU permits through administrative review.
Garage Conversion ADU
A garage conversion transforms an existing detached garage into a livable dwelling unit. Because the basic structure already exists, this is typically the most cost-effective ADU option. Garage conversions work especially well on properties with alley access, where parking isn't dependent on the garage.
TYPICAL COST
$80,000 – $130,000
SIZE RANGE
300 – 600 sq ft
TIMELINE
2–4 months construction
Advantages
- Most affordable ADU type
- Fastest construction timeline
- Existing structure reduces costs
- Lower utility connection costs
Considerations
- Limited by garage size
- Loss of garage parking/storage
- May require foundation upgrades
- Layout constrained by existing structure
Ideal For
Homeowners with detached garages (especially alley-accessed) who can accommodate parking elsewhere. Common in older Denver neighborhoods, Englewood, Wheat Ridge, and Edgewater.
Permit Requirements
Requires change-of-use permit plus building permits for residential conversion. Includes egress window requirements, insulation upgrades, and utility modifications.
Basement ADU
A basement ADU converts your home's existing basement into a separate, legal dwelling unit with its own entrance. This option causes the least disruption to your property's exterior footprint and can be completed relatively quickly compared to new construction.
TYPICAL COST
$100,000 – $180,000
SIZE RANGE
500 – 1,000 sq ft
TIMELINE
3–5 months construction
Advantages
- No change to exterior property footprint
- Moderate cost
- Existing space reduces structural work
- Often has existing plumbing rough-ins
Considerations
- Requires separate exterior entrance
- Egress window requirements
- Ceiling height may be limiting
- Shared walls with primary home
Ideal For
Homes with full, unfinished basements and sufficient ceiling height (typically 7+ feet). Especially popular in Northglenn, Thornton, Centennial, and older Denver neighborhoods with ranch-style homes.
Permit Requirements
Requires building permit for residential conversion. Key requirements include separate exterior entrance, egress windows in bedrooms, fire separation between units, and independent HVAC.
Attached Addition ADU
An attached ADU is a new addition connected to your existing home with its own private entrance. This option works well for homeowners with limited yard space who still want to add a self-contained dwelling unit to their property.
TYPICAL COST
$150,000 – $280,000
SIZE RANGE
400 – 900 sq ft
TIMELINE
3–5 months construction
Advantages
- Works on smaller lots
- Shared wall reduces costs vs. detached
- Can blend seamlessly with home architecture
- Easier utility connections
Considerations
- Less privacy than detached
- Shared wall with primary home
- Limited layout flexibility
- May affect primary home's exterior appearance
Ideal For
Homes with limited yard space but sufficient lot coverage allowance. Good for multigenerational living where proximity to the main home is preferred. Common in Cherry Hills Village, Parker, and suburban communities.
Permit Requirements
Requires building permit similar to a home addition. Must meet ADU requirements including separate entrance, full kitchen and bathroom, and fire separation from primary dwelling.
Not Sure Which ADU Type Is Right for You?
We'll assess your property for free and recommend the ADU type that makes the most sense for your lot, budget, and goals.