Attached ADU
Build an Attached ADU in Colorado
An attached ADU is built as an addition or conversion connected directly to your existing home. It shares at least one wall but functions as a fully independent living space with its own entrance, kitchen, and bathroom.
Benefits of an Attached ADU
Why Choose an Attached ADU
An attached ADU offers a cost-effective way to expand your home while maintaining privacy and independence for occupants. Because it connects to the primary residence, construction and utility integration are often more affordable compared to detached units. Attached ADUs are especially popular in Colorado neighborhoods where lot size or setback rules limit standalone structures.
Lower construction costs compared to detached units
Easier and more affordable utility connections
Ideal for multigenerational living
Maintains backyard and outdoor space
Blends seamlessly with your existing home design
Common Layouts & Options
An attached ADU can be designed as an addition, internal conversion, or vertical expansion. Layout flexibility allows homeowners to maximize square footage while keeping the design cohesive with the main home.
Rear Addition ADU (400–700 sq ft)
Built onto the back of the home with a private entrance, full kitchen, living area, bedroom, and bathroom. A popular solution for rental income or in-law housing.
Side-Yard or Bump-Out ADU (350–600 sq ft)
Extends outward from the main structure, ideal for compact Colorado lots. Efficient layout with full living amenities.
Above-Garage Attached ADU (500–900 sq ft)
Constructed over an existing garage, offering separation while remaining structurally connected. Great for maximizing vertical space.
Two-Story Extension (600–1,000 sq ft)
Adds significant square footage with private lower or upper-level living quarters.
How much does it cost to build an attached ADU in Colorado?
Several factors influence your final project cost. For a personalized estimate, visit our ADU Costs in Colorado page or contact us for a free consultation.
Extent of structural modifications to the main home
Foundation expansion requirements
Plumbing, HVAC, and electrical system upgrades
Interior finishes and customization level
Permit, zoning, and city review fees
Energy efficiency upgrades required by Colorado code
How It Works
Your Colorado ADU Journey in 5 Steps
01
Free Consultation
Discuss your goals, budget, and property potential (zoning check included).
02
Design & Planning
Custom floor plans and 3D renderings that complement Colorado’s unique architectural styles.
03
Permits & Approvals
We handle the complex Denver/Boulder/Aurora permitting and utility tap fees.
04
Construction
Expert build-out using climate-appropriate materials and energy-efficient systems.
05
Final Walkthrough
Inspect every detail and ensure your new space is move-in ready.
Permits & Considerations
Attached ADU regulations vary by city. Denver, Boulder, Fort Collins, and Colorado Springs each have unique zoning codes and integration requirements.
Colorado-specific factors include:
Fire separation and wall rating requirements
Separate exterior entrance compliance
Building code integration with the primary home
Energy efficiency standards
Setback and lot coverage limits
FAQs
Homeowners Questions on Attached ADUs
Are attached ADUs legal in Colorado?
Yes, many Colorado cities and counties allow detached ADUs, but zoning rules, lot size requirements, and design standards vary by municipality. Some areas have specific regulations regarding owner occupancy, maximum square footage, height limits, parking requirements, and setback distances. It’s important to review your local zoning code or work with a knowledgeable ADU builder who understands Colorado’s city-specific guidelines.
Is an attached ADU cheaper than a detached ADU?
Almost certainly yes if you live in an urban or suburban “subject jurisdiction.” Thanks to Colorado’s HB24-1152, most cities along the Front Range are now required to allow at least one ADU on any lot with a single-family home. Furthermore, the law now prevents many HOAs from flat-out banning ADUs, though they can still enforce “reasonable” design standards.
Do I need a separate entrance for an attached ADU?
Yes, most Colorado cities require a private exterior entrance for the unit.
Can I convert part of my home into an attached ADU?
Yes, provided zoning allows it and the space meets building, fire, and safety codes.
Will an attached ADU increase my property value?
Typically yes. Adding livable square footage and rental potential can significantly increase resale value.
Start Your Attached ADU Project Today
We help you build your dream detached ADU every step of the way. Get in touch with one of our experts to start planning your ADU project.