Navigating ADU laws can be a maze. As ADU projects increase in popularity throughout Colorado, municipalities have relaxed regulations in some regards, but have become stricter in others.
Want to find out how challenging it will be to build an ADU on your Boulder or Denver property? Learn more about different ADU regulations in this article.
Key Takeaways:
- Denver is the gold standard for ADU builds in Colorado. It’s easier to get started, since Denver has eliminated mandates like owner-occupancy and parking.
- Boulder has traditionally been a difficult municipality in which to build; however, it’s recently loosened up its regulations to align with state laws.
- Suburbs are still transitioning their rules, and tend to be the most difficult place to build ADUs in comparison to Denver and Boulder.
Denver ADU Rules
While the whole state of Colorado has made strides toward opening up the opportunity for accessory dwelling unit builds, Denver has become the gold standard for ease and flexibility.
Denver has aggressively removed barriers in an effort to make ADUs more accessible and make housing more affordable.
As of late 2024, ADUs are allowed in all residential zones, which means no more expensive rezoning hearings. In addition, you do not have to live on-site, now that owner-occupancy mandates have been lifted. This gives you options for your Denver ADU — you can use it as a flexible family space, a rental unit, or an investment vehicle.
Previously, ADUs in Denver required dedicated parking spots. If you didn’t already have space, you may have been required to pave one, making builds more expensive. Now, this has been lifted, which adds less stress for homeowners!
Finally, Denver offers a good amount of flexibility in how much square footage you can have based on your lot size. Size tiers include:
- Lots less than 6,000 sq ft: Up to 650 sq ft.
- Lots between 6,000–7,000 sq ft: Up to 864 sq ft.
- Lots over 7,000 sq ft: Up to 1,000 sq ft.
Little Home Builder offers ADUs with footprints that work for any lot size — our one-bedroom Autumn model comes in at an efficient 576 square feet!
Boulder ADU Rules
Boulder is a more “premium” market, which makes building an ADU slightly more challenging than in Denver. But if you are a Boulder homeowner who wants a tiny home, you’re in luck. Boulder may not be as favorable as Denver, but it has still relaxed its restrictions from previous years.
As of March 2025, Boulder has removed a rule limiting how many ADUs could be in one neighborhood. Boulder also now allows larger ADUs up to 1,000 square feet, if attached. Otherwise, detached units are generally capped at 800 sq ft.
Boulder does have extremely strict energy guidelines and safety rules. The requirements for fire suppression in detached ADUs, for example, can add significant cost to the project.
ADU Rules in Colorado Suburbs
Rules and regulations vary across Colorado suburbs, but many of them have stricter rules or unique regulations. For example:
Arvada uses a sliding scale based on lot size. For most suburban lots from 6,000 to 12,000 square feet, the cap is 850 sq ft. ADUs in Arvada require architectural compatibility, meaning the ADU must look like the main house.
Wheat Ridge is one of the more progressive suburbs for building accessory dwelling units. They allow ADUs up to 1,000 sq ft or 50% of the main house size. However, they still have an owner-occupancy requirement for short-term rentals. Also, utility costs are high in Wheat Ridge as they are mandating new water and sanitary taps, rather than allowing ADUs to run off the existing systems.
Jefferson County, an unincorporated community, requires a minimum lot size of 7,500 sq ft for a detached ADU. Anything smaller must be an attached/internal unit.
Where is the Best Place to Build an ADU in Colorado?
While ADUs are a viable option in many places across Colorado, Denver has made them an easy and attractive way to add space or rental opportunities on your property.
Here are three reasons why Denver is a winner for homeowners:
1. In Denver, ADU permits are administrative. There are no public hearings where neighbors can block your project.
2. Because Denver has the highest rent-per-square-foot in the state and the most flexible rental rules, you can expect to see a return on investment faster.
3. Denver’s unique urban grid with rear alleys makes detached ADUs much easier to build and more private than in suburban cul-de-sacs.
At Little Home Builder, we’ve spent years mastering Denver’s zoning so you don’t have to. We’ve built ADUs in Denver from garage conversions to loft spaces. For example, this build in Denver that packs a lot of natural light and open space into an efficient 477 square foot space. This ADU in a Denver backyard includes a parking space, front porch, and privacy fence. Inside, we created a streamlined and modern kitchen and bath to match. View the project here.
For a truly simple and turnkey ADU build in Denver, Boulder, Arvada, or beyond, get in touch with Little Home Builder.
