ADU (Additional Dwelling Units)

ADU (Additional Dwelling Unit) Design & Construction in Colorado

Unlock the full potential of your property with a custom Accessory Dwelling Unit (ADU) from PrimeStone. Whether you’re building an ADU for rental income, multi-generational living, or added space for guests, our team delivers engineered, code-compliant design and build solutions tailored to Colorado’s unique requirements.

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.

What Is an ADU?

An ADU (Accessory Dwelling Unit) is a secondary housing unit on the same property as a primary residence. ADUs can be:

Detached units (stand-alone structures)

Attached units (connected to the main house)

Garage conversions

Basement or attic conversions

ADUs are a smart solution for rental income, housing family members, aging-in-place design, home offices, or short-term rentals such as Airbnb.

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.

Site Evaluation & Planning

Zoning review and lot feasibility analysis

Structural and foundation assessment

Utility capacity and connection planning

Egress and code compliance evaluation

Design & Engineering

Custom architectural design

Structural engineering and load analysis

Permit-ready drawings and specifications

Energy code compliance planning

Construction Services

Foundation, framing, roofing, and exterior finishes

Plumbing, electrical, and HVAC systems

Insulation, drywall, and interior finishes

Kitchen and bathroom build-outs

Flooring, lighting, cabinetry, and fixtures

Permit Management & Inspections

Submit plans and handle permitting

Coordinate inspections with local jurisdictions

Ensure engineering compliance at every stage

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

1. Initial Consultation & Feasibility

We evaluate your property, discuss goals, and determine what type of ADU will meet your needs and local zoning requirements.

2. Design & Engineering

Our team develops customized plans that balance aesthetics, code compliance, and structural considerations.

3. Permitting & Approvals

We handle all permitting and coordinate with local authorities so that your project moves smoothly.

4. Construction & Project Management

From site prep to final finishes, we execute the build with oversight and consistent communication.

5. Final Inspection & Handover

After inspection and approvals, we deliver a finished ADU that is safe, functional, and ready for occupancy.

Why Choose PrimeStone for ADUs in Colorado?

Structural engineer–owned design-build company

End-to-end ADU planning, design, permitting, and construction

Code-compliant structural and architectural expertise

Transparent pricing, clear scopes of work, and project communication

Customized solutions for rental units, in-laws suites, and accessory living spaces

Trusted by homeowners, investors, and real estate professionals

Serving the Denver Metro Area & Colorado Front Range

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.

Schedule Your ADU Consultation

Ready to explore the possibilities of an Accessory Dwelling Unit on your property?

Contact PrimeStone today for a consultation and detailed estimate.

Get a Quote

ADU FAQ — Accessory Dwelling Units in Colorado

What is an ADU?

An ADU (Accessory Dwelling Unit) is a secondary housing unit on the same property as the main home. It can be detached, attached, or a conversion of an existing space like a garage or basement.

Do I need a permit to build an ADU in Colorado?

Yes. ADU construction requires permits for zoning, building, electrical, plumbing, and mechanical work. PrimeStone manages the entire permitting process to ensure compliance.

How long does it take to build an ADU?

Typical ADU projects take 4–9+ months, depending on design complexity, site conditions, permitting timelines, and finishes. We provide a customized timeline during planning.

Can you help determine if my property qualifies for an ADU?

Yes — we perform a site evaluation and zoning feasibility review to determine if your lot meets local ADU regulations, setbacks, and size limits.

How much does an ADU cost in Colorado?

Costs vary by design, size, location, and finishes. Most detached ADUs start between $180,000–$300,000+, and garage or interior conversions can cost less. We provide detailed estimates during the design phase.

Do ADUs increase property value?

Yes — well-built ADUs can increase property value and generate rental income. They also offer flexibility for multi-generational living or home offices.

Can you convert my garage or basement into an ADU?

Absolutely. We handle attached ADUs, garage conversions, and basement conversions — all engineered to meet structural and code requirements.

What makes PrimeStone different from other ADU builders?

PrimeStone is structural engineer–owned, meaning every ADU project benefits from engineering oversight, code-compliant design, and construction that prioritizes structural safety and long-term performance.

Can an ADU have a kitchen and bathroom?

Yes — most ADUs include a full kitchen and bathroom, though utility capacity and permitted layout may vary. We design systems to meet local code and functional use.

Are ADUs allowed everywhere in Colorado?

ADU regulations vary by municipality. We conduct a zoning review during evaluation to determine what is allowed on your specific property.

Do you handle utilities and HVAC for ADUs?

Yes. We design and build complete systems including plumbing, electrical, HVAC, and insulation so your ADU is comfortable and efficient.

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ADU (Additional Dwelling Units)