At ArcWest Architects we’re always keeping tabs on local zoning and code changes so that we can keep our clients as informed as possible. In recent years, Accessory Dwelling Unit (ADU) requirements have been evolving regularly, making these types of additions more accessible to homeowners. Here’s a brief summary of current legislation regarding construction of ADUs in Colorado and Denver and what this means to you as you consider adding an ADU to your Denver property.
November 2024 State-level legislation to more broadly allow ADUs
Colorado House Bill 24-1152 requires cities of certain size thresholds to allow ADUs. This is the same requirement that both Oregon and Washington have. The bill also requires jurisdictions to remove “restrictive design or dimension standards.” To do this, subject jurisdictions must:
- Allow an ADU of up to at least 500 sq ft.
- Not require off-street parking.
- Not require the owner to occupy the property.
- Reduce side and rear setbacks to 5ft (with some sub-optimal caveats).
- Not have minimum lot size requirements.
- Not have special design standards for prefabricated ADUs (though Building Coder standards will still be enforced).
City-level changes to ADU requirements for Denver in 2023
In 2023, the city of Denver implemented changes to its ADU requirements, allowing for greater flexibility, including:
- More flexibility to create a 2-story ADU than the previous 1.5 story limit.
- Suburban neighborhood ADUs generally must be 1-story with rear and side setbacks (depends on the neighborhood).
- The building lot coverage exemption in place for vehicle parking is extended to ADUs making 1-story easier to pursue. A single story can better serve occupants who are elderly or disabled.
- Zoning barriers that previously limited the conversion of existing structures like garages into ADUs were removed.
- The maximum floor area of ADUs for smaller lots increased, allowing these lots the option of building ADUs that can serve a family. This can help keep multi-generational families on the same property.
- City officials left in place that the owner must live on the property (a big barrier).
- You can add an ADU to a duplex.
Denver’s current requirements to build an ADU
As of January 2025, these are Denver’s current ADU requirements:
- Your ADU must have its own address.
- If you’re in a single-unit zone district (read: you live in a standalone house), you (the owner) must live on-site, either in the primary residence or in the ADU.
- Whenever feasible, the dwelling’s utilities must be shared with the primary house.
- You’re going to pay almost all the same permitting fees as you would if you were building a primary residence (bummer, we know).
- In single-unit zone districts, you can’t sell your ADU separately from the main property (no, not even to Granny).
- You may not put the “I” in DIY and build your own ADU—unless you’re a licensed general contractor (GC). Only GCs are allowed to construct these units in Denver.
- A new rule starting March 2022 requires landlords to have a rental license, so be sure to check local rules/guidelines.
Here is a summary of Denver’s Citywide Accessory Dwelling Units (ADUs) project which updated building standards and implemented State-level legislation for ADUS in November 2024. The proposed measure and changes went into effect December 16, 2024. For more information on the project, visit the project webpage.
Denver Citywide ADUs Text Amendment Summary
The following summary describes the proposed changes by topic.
ADU Allowance & Detached ADU Building Form
- Residential areas that currently don’t allow ADUs would be able to build them.
- Detached ADUs (separate structures as opposed to a basement ADU or other attached unit) will be allowed in these areas and would follow design standards based on their neighborhood context.
Removal of Duplicative Zone Districts
- The proposed change to allow ADUs in all residential areas of the city would allow 16 zone districts within the Denver Zoning Code (DZC) to be deleted since their sole purpose is to allow ADUs. The “1-districts” (zone districts that end with the number 1) are identical to their non-1 counterparts with the only difference being the allowance of ADUs. The “1-districts” are no longer needed, and their removal can help simplify the DZC.
- The text amendment will be accompanied by a map amendment that would rezone the properties from the “1-districts” to the most directly corresponding zone district. For example, U-SU-A1 would be rezoned to U-SU-A, etc. The proposed map amendment would not change any zoning requirements that apply to rezoned properties.
Follow State Law on Owner Occupancy
- The new ADU state law, passed in May 2024, limits when jurisdictions can impose an owner occupancy requirement (that the owner of the property reside in either the primary home or ADU). To comply with state law, the Citywide ADUs text amendment would require owners reside in either the primary residence or ADU only at the time of permit application.
ADUs in Site Development Plans
- The permitting process for ADUs on properties within a site development plan (SDP) or Planning Building Group (Former Chapter 59’s version of an SDP) requires extra layers of review and a full SDP amendment because of how these properties were originally approved and developed. The Citywide ADUs text amendment proposes to ease the review process for ADUs within these plans. It would allow an ADU to be approved by a zoning permit if the ADUs doesn’t result in more building cover on the site. An ADU that does increase building cover could be approved as an SDP modification.
Former Chapter 59 Bridge Amendment
- ADUs would be allowed in all residential areas in Former Chapter 59 zone districts. Bridge amendments are proposed to detail the design standards that ADUs in these districts would need to follow.
From Denvergov.org (Nov 2024)
If you’re considering an ADU on your property, we invite you to reach out for an initial consultation with an ArcWest expert by filling out this brief inquiry form: https://arcwestarchitects.com/project-category/adu/. And, if you’re looking for more information, here are some helpful resources to learn more:
https://arcwestarchitects.com/project-category/adu
https://www.instagram.com/explore/search/keyword/?q=%23accessorydwellingunit
https://www.5280.com/everything-you-need-to-know-about-building-an-adu/https://www.aarp.org/livable-communities/housing/info-2019/accessory-dwelling-units-adus.html