Building an Accessory Dwelling Unit (ADU) on your Denver property is one of the smartest moves a homeowner can make right now. The City of Denver has relaxed its zoning code in recent years, opening the door for more homeowners to add a secondary living space to their lot. Whether you want to house an aging parent, create a private guest suite, or add a rental unit that helps cover your mortgage, an ADU puts your property to work.

But a successful ADU project takes careful planning. You need to understand Denver’s specific zoning rules, know which permits to pull, choose between a new build and a garage conversion, and find a builder who has done this before. This guide walks through every stage of the process so you can move forward with confidence.

What Is an Accessory Dwelling Unit?

An Accessory Dwelling Unit, or ADU, is a self-contained secondary home located on the same lot as a primary single-family house. You may have heard them called granny flats, in-law suites, backyard cottages, or carriage houses. Whatever the name, the defining feature is the same: an ADU includes its own entrance, kitchen, bathroom, and sleeping area. It is a fully independent living space, not just an extra bedroom.

ADUs are different from duplexes. A duplex consists of two primary residences on one lot, while an ADU is always secondary to the main home. ADUs also differ from tiny homes, which are often mobile structures. A legal ADU sits on a permanent foundation and meets all local building codes for safety and livability.

Denver homeowners build ADUs for many reasons. Some create private quarters for family members who want to live nearby without sharing walls. Others use them as dedicated home offices, art studios, or guest suites. And many homeowners build ADUs specifically to generate rental income, a strategy that can add thousands of dollars in annual revenue while increasing the property’s overall market value.

Types of ADUs You Can Build in Denver

ADUs come in several forms, and the right choice depends on your property layout, your goals, and your timeline. Here are the most common options Denver homeowners consider:

• Detached ADU: A standalone structure built in the backyard, separate from the main house. This is the most flexible option for floor plan design and often delivers the best rental returns because of its privacy.
• Attached ADU: A new addition connected to the main home, such as a bump-out or wing extension. This option shares a wall or roof with the primary house and can be easier to connect to existing utilities.
• Garage Conversion: Transforming an existing attached or detached garage into a living space. Garage conversions are popular because the basic structure (walls, roof, foundation) is already in place, which can speed up the project timeline.
• Basement Apartment: Converting an existing basement into an independent unit with a separate entrance. Denver’s climate makes basements common, so many properties already have the shell in place.
• Above-Garage Unit: Building a living space on top of an existing or new garage, sometimes called a carriage house. This approach maximizes your lot by stacking living space over parking or storage.

Each type has its own set of zoning considerations, construction requirements, and budget implications. A licensed home builder can help you evaluate which option makes the most sense for your specific property.

Denver’s ADU Zoning Rules and Regulations

Denver has become one of the more ADU-friendly cities in Colorado, but there are still rules you need to follow. Understanding these regulations before you start planning will save you time, money, and headaches down the road.

Is Your Property Eligible?

The first step is confirming that your lot qualifies for an ADU. Denver allows ADUs in most single-family residential zones. Your eligibility depends on several factors:

• Zoning district: ADUs are permitted in SU (Single Unit), TU (Two Unit), and many other residential zone districts throughout the city.
• Lot size: Your lot must meet minimum size requirements, which vary by zone. In general, a standard 6,000-square-foot lot in a single-unit zone qualifies.
• Existing structures: You must have a primary residence on the property. The ADU is secondary to this main home.

Check your specific zoning by visiting the Denver Community Planning and Development (CPD) website or contacting their office directly. They can confirm your zone district and tell you exactly what is allowed on your lot.

Size and Height Limits

Denver caps ADU size based on your lot and zone district. Key limits include:

• Square footage: ADUs are typically capped at 1,000 square feet or a percentage of the primary home’s square footage, whichever is less. The exact cap depends on your zone district.
• Height: Detached ADUs generally cannot exceed 24 feet in height, though some districts allow taller structures if the design meets specific criteria.
• Floor Area Ratio (FAR): The total building coverage on your lot, including both the main home and the ADU, must stay within your zone district’s FAR limit. This prevents over-building on smaller lots.

Setback Requirements

Setbacks determine how close your ADU can sit to property lines. Denver requires minimum distances from side, rear, and front lot lines. For most detached ADUs, expect a minimum 5-foot setback from side and rear property lines. Your builder should verify the exact requirements for your specific lot before finalizing the design.

Owner-Occupancy Rule

One regulation that catches some homeowners off guard is Denver’s owner-occupancy requirement. The property owner must live on-site, either in the main house or in the ADU. This means you cannot rent out both the primary home and the ADU to separate tenants unless local rules change. This requirement is fundamental to Denver’s ADU policy and affects your investment strategy.

The Permitting Process for Denver ADUs

Building an ADU in Denver requires permits, and the process involves several steps. Working with an experienced contractor who knows the local permitting landscape can make this much smoother.

Permits You Will Need

A typical ADU project requires multiple permits:

• Zoning permit: Confirms your project complies with land use rules (setbacks, height, lot coverage).
• Building permit: Covers the structural, mechanical, electrical, and plumbing work.
• Sewer/water tap permits: Required if your ADU needs new utility connections.
• Right-of-way permit: Needed if any work affects the public sidewalk or street.

How to Submit Your Plans

Denver’s Community Planning and Development (CPD) office handles permit applications. You will need to submit architectural drawings, a site plan showing the ADU’s location on your lot, and structural engineering documents. The review process typically takes 4 to 8 weeks, though timelines vary based on project complexity and the city’s current workload.

A skilled builder handles the permit process for you. At Faros Construction Services, we manage the full permitting workflow so you can focus on design decisions rather than paperwork.

Garage to ADU Conversion: A Popular Denver Option

Converting an existing garage into an ADU is one of the most popular approaches for Denver homeowners, and for good reason. Your garage already has a foundation, walls, and a roof. That existing structure reduces the scope of new construction, which can shorten your timeline and lower your upfront investment compared to building from scratch.

Full vs. Partial Conversion

You have two main paths for a garage conversion:

• Full conversion: The entire garage becomes a living space. This means adding insulation, flooring, plumbing, electrical, HVAC, and finishing the interior to residential standards. You lose garage parking and storage but gain a complete living unit.
• Partial conversion: Part of the garage becomes living space while the rest remains a garage or storage area. This is a good compromise if you still need covered parking or a workshop.

What Affects a Garage Conversion Project

Several factors shape the scope of a garage conversion:

• Structural condition: Your garage’s foundation, framing, and roof need to meet residential building codes. Some older garages require foundation upgrades or structural reinforcement.
• Plumbing and electrical: Adding a kitchen and bathroom means running new plumbing lines and upgrading the electrical panel. The distance from your main home’s utility connections affects the complexity.
• Insulation and HVAC: Most garages are uninsulated. You will need wall and ceiling insulation plus a heating and cooling system that meets Denver’s energy code.
• Denver building codes: The converted space must meet all building codes for habitable rooms, including minimum ceiling height, natural light, ventilation, and egress windows.

Start by assessing your current garage’s condition and talking to a qualified contractor who can walk the space with you and outline what the conversion will involve.

Custom ADU Design: Building Exactly What You Need

If you have the space and the vision, a custom ADU gives you full control over the design. Unlike prefabricated or standard plans, a custom build starts with your specific property and your goals. You choose the floor plan, the materials, the finishes, and the layout that works best for how you plan to use the space.

What Makes a Custom ADU Different

Standard ADU plans are off-the-shelf designs that work for many properties but offer limited flexibility. A custom ADU is designed around your lot’s unique characteristics, including slope, orientation, existing landscaping, views, and proximity to the main home. The result is a space that feels intentional rather than generic.

Custom design is especially valuable when your property presents challenges. A sloped backyard, an oddly shaped lot, mature trees you want to preserve, or specific Denver zoning constraints can all be addressed through thoughtful custom design. An experienced builder works with you and an architect to solve these site-specific problems from the start.

Key Design Decisions

When planning a custom ADU, focus on these decisions early:

• Purpose: How will the space be used? A rental unit needs a different layout than a home office or a suite for aging parents. Rental ADUs benefit from a separate entrance and clear separation from the main home.
• Floor plan efficiency: In a small space, every square foot counts. Open floor plans with multipurpose rooms maximize livability. Think about storage, natural light, and flow between the kitchen, living area, and bedroom.
• Architectural style: Your ADU should complement the main house. Matching rooflines, siding materials, and window styles creates a unified look that adds value to the whole property.
• Energy efficiency: Denver’s climate demands good insulation, efficient windows, and a reliable HVAC system. Building to high energy standards reduces long-term operating expenses and makes the space more comfortable year-round.
• Accessibility: If the ADU is for aging parents or anyone with mobility needs, plan for single-story living, wider doorways, a walk-in shower, and grab bars from the start. Retrofitting later is more expensive.

How to Choose the Right ADU Builder in Denver

Your builder is the most important partner in your ADU project. The right contractor brings experience with Denver’s specific zoning rules, a track record of completed ADU projects, and the ability to manage every stage from design through final inspection.

What to Look for in an ADU Contractor

Not every general contractor has ADU experience. When evaluating builders, focus on these qualifications:

• ADU-specific experience: Ask how many ADU projects they have completed in the Denver metro area. A contractor who has built multiple ADUs understands the common challenges, from navigating Denver’s permit process to maximizing small floor plans.
• Full-service capability: The best ADU builders handle everything: design, permitting, construction, and final inspections. A full-service approach means fewer handoffs and fewer opportunities for miscommunication.
• Licensing and insurance: Verify that the contractor holds a valid Colorado contractor’s license and carries general liability insurance and workers’ compensation coverage. Ask for proof before signing any agreement.
• References and reviews: Talk to previous ADU clients. Ask about communication, timeline accuracy, and how the builder handled unexpected issues. Online reviews provide additional perspective, but direct references are more valuable.
• Clear communication: A good builder explains the process, provides a detailed timeline, and keeps you updated throughout the project. If a contractor is hard to reach before you hire them, that pattern will continue during construction.

Questions to Ask Before Hiring

Before committing to a builder, get clear answers to these questions:

1. How many ADU projects have you completed in Denver?
2. Do you handle the full permit process, or is that my responsibility?
3. What is your estimated timeline from design to move-in?
4. How do you handle change orders or unexpected issues during construction?
5. What warranty do you provide on your work?
6. Can I speak with two or three recent ADU clients?

At Faros Construction Services, we bring over 30 years of construction experience to every ADU project in the Denver metro area. Ricardo Alfaro, our owner, personally oversees each build from start to finish. That hands-on approach means your project gets the attention it deserves. Learn more about our home building services.

The ADU Construction Process: From Design to Move-In

A well-run ADU project follows a predictable sequence. Knowing what to expect at each stage helps you plan your time and make decisions efficiently.

Step 1: Initial Consultation and Site Assessment

The project begins with an on-site visit. Your builder walks the property, evaluates the lot, checks for potential challenges (slope, drainage, utility access, tree roots), and discusses your goals. This visit sets the foundation for everything that follows.

Step 2: Design and Planning

Based on the site assessment, your builder or architect creates a design that meets your needs and complies with Denver’s zoning rules. You will review floor plans, exterior elevations, material selections, and a detailed project scope. This is when you finalize decisions about layout, finishes, and any special features.

Step 3: Permitting

Your builder submits plans to Denver’s Community Planning and Development office. The review and approval process typically takes 4 to 8 weeks. During this time, you may need to respond to plan check comments or provide additional documentation.

Step 4: Construction

Once permits are approved, construction begins. A detached ADU typically takes 4 to 6 months to build, depending on size and complexity. Garage conversions can often be completed in 2 to 4 months. Your builder manages the day-to-day work, coordinates subcontractors, schedules city inspections, and keeps you informed of progress.

Step 5: Final Inspections and Certificate of Occupancy

After construction is complete, the city conducts final inspections covering structural, electrical, plumbing, mechanical, and fire safety systems. Once everything passes, Denver issues a Certificate of Occupancy (CO), which means your ADU is legally approved for habitation.

Step 6: Move-In and Maintenance

With the CO in hand, your ADU is ready for its intended use. Your builder should provide maintenance guidance and warranty information. Regular upkeep, including HVAC servicing, gutter cleaning, and exterior inspections, keeps the space in top condition for years to come.

Why Denver Homeowners Are Building ADUs Now

Several trends are driving ADU construction in the Denver metro area:

• Housing flexibility: Denver’s updated zoning code has removed many of the barriers that previously made ADU construction difficult or impossible. More properties than ever now qualify.
• Multigenerational living: More families want to keep aging parents or adult children close by while maintaining separate living spaces. An ADU provides independence with proximity.
• Rental income potential: With Denver’s strong rental market, an ADU can generate meaningful monthly income. Many homeowners use this revenue to offset mortgage payments, fund home improvements, or build savings.
• Property value: A well-built ADU adds usable square footage and functional flexibility to your property, both of which increase market value. Buyers increasingly look for properties with ADUs because of the income potential and versatility.
• Home office demand: Remote work has made dedicated office space a priority for many homeowners. A backyard ADU creates a true separation between work and home life that a spare bedroom cannot match.

The combination of relaxed regulations, strong demand, and clear financial benefits makes right now an excellent time to explore ADU construction on your Denver property.

ADU Construction in the Denver Metro Area: Local Considerations

Building an ADU in Denver comes with location-specific factors you should plan for:

• Climate: Denver’s wide temperature swings (from below zero in winter to 90+ degrees in summer) demand proper insulation, energy-efficient windows, and a reliable HVAC system. Snow loads also affect roof design for detached structures.
• Soils: Many Denver-area properties have expansive clay soils that can shift with moisture changes. Your builder should conduct a soil test and design the foundation accordingly. Proper drainage around the ADU is also critical.
• Utility connections: Connecting water, sewer, gas, and electric to a detached ADU involves trenching and potentially upgrading your main service panel. These connections need to be planned early in the design phase to avoid surprises.
• Neighborhood context: Different Denver neighborhoods have different character and density levels. A well-designed ADU respects the existing streetscape and adds gentle density without disrupting the neighborhood feel. This also means working within any HOA rules that may apply to your property.

Faros Construction Services has been building in the Denver metro area for years, serving homeowners across Denver, Aurora, Lakewood, Littleton, Arvada, Westminster, Highlands Ranch, Englewood, Golden, Thornton, Parker, Castle Rock, and Centennial. View our full service area.

Frequently Asked Questions About ADU Construction in Denver

Can I build an ADU on my Denver property?

Most single-family residential lots in Denver now allow ADUs under the updated zoning code. Your eligibility depends on your specific zone district, lot size, and existing structures. Contact Denver’s Community Planning and Development office or ask your builder to verify your property’s qualifications before starting the design process.

What types of ADUs can I build?

Denver allows detached ADUs (standalone backyard structures), attached ADUs (additions to the main home), garage conversions, basement apartments, and above-garage carriage houses. The best option for your property depends on your lot layout, existing structures, and how you plan to use the space.

Do I need to live on the property if I build an ADU?

Yes. Denver’s current regulations require the property owner to live on-site, either in the primary residence or in the ADU. You cannot rent out both the main home and the ADU to separate tenants.

How long does it take to build an ADU in Denver?

The full process, from initial design through move-in, typically takes 6 to 12 months. Permitting accounts for 4 to 8 weeks, and construction ranges from 2 to 4 months for a garage conversion up to 4 to 6 months for a new detached ADU. Timelines vary based on project complexity and the city’s permit review workload.

Can I convert my garage into an ADU?

Yes, garage conversions are one of the most popular ADU options in Denver. Both attached and detached garages can be converted, provided the finished space meets all building codes for habitable rooms, including minimum ceiling height, natural light, ventilation, and egress requirements. A full conversion transforms the entire garage into living space, while a partial conversion keeps some area for storage or parking.

What permits do I need to build an ADU?

ADU projects in Denver typically require a zoning permit, building permit, and potentially sewer/water tap permits and right-of-way permits. Your builder should handle the full permit application process, including submitting architectural drawings and responding to any plan review comments from the city.

How do I choose the right ADU builder?

Look for a builder with specific ADU experience in the Denver metro area, full-service capability (design through final inspection), proper licensing and insurance, strong client references, and clear communication. Ask how many ADU projects they have completed and request to speak with recent clients about their experience.

Start Your Denver ADU Project with Faros Construction

Building an ADU is a significant project, and the results should last for decades. At Faros Construction Services, we bring the experience, local knowledge, and hands-on approach needed to deliver an ADU that meets your goals and stands up to Denver’s demanding climate.

We handle every step: site assessment, design, permitting, construction, and final inspection. Ricardo Alfaro, our owner and general contractor with over 30 years of experience, personally manages each project. That means you get direct access to the person making decisions on your build, not a project manager relaying messages.

Whether you are converting a garage, building a detached backyard cottage, or adding an attached unit, we can help you turn your ADU vision into reality. Contact us for a free consultation and let us show you what is possible on your property.