ADU (Additional Dwelling Units)
Denver has some of the most ADU-friendly zoning in the country and PrimeStone Construction Group helps you take advantage of it. As a licensed, structural engineer–owned ADU builder, we design and construct accessory dwelling units for rental income, multi-generational living, and long-term property value throughout Denver, Aurora, Lakewood, Boulder, and the greater Front Range. We handle the entire process: zoning eligibility, design, permits, and construction.
What is an ADU? An Accessory Dwelling Unit (ADU) also called a granny flat, mother-in-law suite, carriage house, or casita is a self-contained secondary home on the same lot as a primary residence. It has its own entrance, kitchen, bathroom, and living/sleeping space, and can be detached, attached, built above a garage, or converted from a basement or garage.
As a structural engineer–owned design-build company, PrimeStone provides homeowners with both architectural insight and engineering expertise — ensuring structurally sound ADU projects that meet local building codes and maximize livability.
We proudly serve the Denver Metro Area and Colorado Front Range, including Denver, Aurora, Highlands Ranch, Centennial, Lakewood, Boulder, and surrounding communities.
An ADU (Accessory Dwelling Unit) is a secondary housing unit on the same property as a primary residence. ADUs can be:
ADUs are a smart solution for rental income, housing family members, aging-in-place design, home offices, or short-term rentals such as Airbnb.
Types of ADUs We Build
Detached ADU (Backyard Cottage / Carriage House)
A standalone unit in your backyard with its own foundation and utilities. The most flexible and highest-value option and the most involved to build. Must sit in the rear portion of your lot per Denver zoning.
Above-Garage ADU
A dwelling unit built above a new or existing garage a smart way to add living space and rental potential without sacrificing yard space.
Garage Conversion ADU
Converting an existing garage into living space. Often more affordable than building from scratch, though many Denver garages need new insulated foundations, plumbing, and electrical. Note: eliminating off-street parking may trigger a parking-compensation requirement.
Basement / Internal ADU
Converting a basement or portion of your existing home into a self-contained unit with its own entrance, kitchen, and bath typically the most cost-effective ADU when the space already exists.
How Much Does It Cost to Build an ADU in Denver, CO?
Building an ADU in Denver typically costs between $150,000 and $350,000+ in 2026, with a typical detached ADU landing around $230,000–$310,000. Even small ADUs require a full kitchen and bath, which are expensive per square foot. Type, size, site conditions, and finish level are the biggest cost drivers.
ADU Type | Estimated Cost (2026) |
Garage conversion (1-story) | $140,000 – $200,000 |
Small detached ADU (400–600 sq ft) | $150,000 – $220,000 |
Mid-size detached ADU (700 sq ft, mid-tier) | $250,000 – $350,000 |
Above-garage / 2-story ADU | $350,000 – $380,000+ |
Additional Denver-specific costs to budget for:
Since the Denver Group Living Code update, ADUs are allowed by-right on most single-family lots meaning a 400–1,000 sq ft unit can typically be permitted without a variance. However, your specific zone, lot size, and setbacks determine what you can build. Key Denver ADU standards include:
Rule | Denver Standard |
Where allowed | By-right in most single-family & many multi-family zones (verify your zone) |
Typical size | 400 – 1,000 sq ft |
Maximum height | 24 feet (bulk-plane limited) |
Detached placement | Generally must sit in the rear 35% of the lot |
Setbacks | Vary by lot width and alley access |
Licensed contractor | Required to pull permits and build |
Yes. Denver allows long-term rental (30+ days) of an ADU with no owner-occupancy requirement. Short-term rental (under 30 days) requires a Denver Short-Term Rental license and DOES require you to live on the property as your primary residence. The STR license costs about $250 per year. You can short-term rent your ADU or your main house but not both at once unless you’re the primary resident of one.
Rental Type | Owner-Occupancy Required? | License |
Long-term (30+ days) | No | No license required |
Short-term (under 30 days) | Yes | Denver STR license (~$250/yr) |
Rental and occupancy rules can change. Confirm current requirements with the City and County of Denver before planning your rental strategy.
Most Denver ADUs take 4 to 8 months from design through final inspection. Feasibility and design run 2–12+ weeks, and permit review can take a few weeks to several months depending on complexity and whether your property is in a historic district.
An ADU is a long-hold asset, not a get-rich-quick investment but it can add significant value and flexibility. In Denver, ADUs can generate long-term rental income in the typical apartment-rent range, and short-term rentals can earn considerably more in the right location (one Denver example estimated around $3,900/month for a well-located short-term rental). Just as important, an ADU adds resale value and gives you options: rental income, a multi-generational compound, a home office, or a guest suite.
Our ADU Design & Construction Services
ADUs are a smart solution for rental income, housing family members, aging-in-place design, home offices, or short-term rentals such as Airbnb.
Because PrimeStone is structural engineer–owned, all ADU designs are reviewed for structural integrity, efficient load management, and full compliance with building codes — giving you confidence in both safety and long-term performance.
Our ADU Process
We evaluate your property, discuss goals, and determine what type of ADU will meet your needs and local zoning requirements.
Our team develops customized plans that balance aesthetics, code compliance, and structural considerations.
We handle all permitting and coordinate with local authorities so that your project moves smoothly.
From site prep to final finishes, we execute the build with oversight and consistent communication.
After inspection and approvals, we deliver a finished ADU that is safe, functional, and ready for occupancy.
Whether it’s your first ADU or you’re expanding your property’s potential, PrimeStone delivers thoughtful design and reliable construction — engineered for safety and long-term value.
Ready to explore the possibilities of an Accessory Dwelling Unit on your property?
Contact PrimeStone today for a consultation and detailed estimate.
ADU FAQ — Accessory Dwelling Units in Colorado
What is an ADU?
Do I need a permit to build an ADU in Colorado?
How long does it take to build an ADU?
Can you help determine if my property qualifies for an ADU?
How much does an ADU cost in Colorado?
Do ADUs increase property value?
Can you convert my garage or basement into an ADU?
What makes PrimeStone different from other ADU builders?
Can an ADU have a kitchen and bathroom?
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