Colorado ADU Law (HB24-1152): What Cities Must Allow

Since June 30, 2025, most cities on Colorado's Front Range and in its other metro areas must let you build one accessory dwelling unit (ADU) on any lot where a single-family house is allowed, approved administratively, without a hearing. The law behind it, HB24-1152, also stops those cities from requiring owner occupancy or new parking in most cases, and from capping ADUs below a size range of 500 to 750 ft². This post walks through what the statute actually says, what a city can still regulate, and how a typical 800 ft² two-bedroom ADU fits under it. Law current as of October 2026.

Who the law covers

HB24-1152 was signed on May 13, 2024. Its mandatory rules apply to "subject jurisdictions", which the bill defines as either:

• a municipality with 1,000 or more residents inside the area of a metropolitan planning organization (MPO), or
• the part of a county that is inside both an MPO area and a census-designated place of 40,000 or more people.

In practice that takes in Denver and most of the metro area around it, plus the cities in Colorado's other MPO regions such as Colorado Springs, Fort Collins and Grand Junction. Smaller mountain towns and rural counties are generally outside the mandate, though they can opt in as "ADU-supportive jurisdictions" to qualify for state grant money. The Colorado Department of Local Affairs (DOLA) publishes the official list; check it on its ADU page before you assume your town is covered.

What a subject jurisdiction must allow

The core rule (C.R.S. 29-35-403, as summarized by the state Division of Local Government) is short: on or after June 30, 2025, a subject jurisdiction "shall allow, subject to an administrative approval process, one accessory dwelling unit as an accessory use to a single-unit detached dwelling" anywhere it allows single-unit detached dwellings. It then lists what the city may not do:

The size language is worth reading carefully. A "restrictive design or dimension standard" includes one that "does not allow for accessory dwelling unit sizes between five hundred and seven hundred fifty square feet". Separately, the law lets a city allow ADUs smaller than 500 or larger than 750 ft², or from keeping the ADU no larger than the main house. So the guaranteed range is 500 to 750 ft²; anything above 750 depends on your city's code.

HB24-1152 also reaches HOAs and planned unit developments in subject jurisdictions: a PUD or covenant cannot ban an ADU outright. HOAs can still apply ordinary design rules, so read your covenants alongside the city code.

What the law does not change

• Building codes. The statute expressly leaves locally adopted life-safety codes in place: building, fire, utility and similar codes. Most Colorado cities build on the International Residential Code with local amendments.
• Impact fees. Cities may keep generally applicable impact fees and development charges. The bill created a state grant program that can help supportive jurisdictions waive or reduce ADU fees and pay for pre-approved plans.
• Short-term rentals. A city may still regulate or ban short-term rental of an ADU or the main house.
• Historic districts. Historic-district design standards and procedures, including demolition review, still apply.
• More than one ADU. The mandate is one ADU per house. A city may allow more, but does not have to.

HB24-1152 passed in the same session as HB24-1313, which sets housing-capacity goals around transit stations in the larger metro cities. The two are separate laws: 1313 is about zoning capacity near frequent transit, 1152 about ADUs on single-family lots. A lot near a station may benefit from both.

An 800 ft² ADU under these rules

FloorGen's 800 sq ft 2-bed ADU template is a detached 40 × 20 ft cottage measured to the outside of its walls: two bedrooms on one end, a 9 × 6 ft bath and a laundry alcove off a short hall, and an open kitchen, dining and living room on the other end. It sits just above Colorado's guaranteed range, so treat it as the upper case: in a city that caps ADUs at 750 ft², shorten it by a couple of feet; where the city allows 800 ft² or more, it works as drawn.

Note the gap between 800 ft² outside and about 700 ft² of net floor. Colorado cities measure ADU size in their own codes, sometimes as gross floor area to the outside of the walls, sometimes as habitable area. Ask which one applies before you size the plan, because 2×6 exterior walls alone cost about 64 ft² on a building this size. Our guide to measuring square footage explains the difference.

Setbacks on a typical Denver-area lot

On a 50 × 125 ft lot, a 40 × 20 ft ADU set across the back of the yard needs the side setbacks a house would have in that zone and a rear setback of no more than 5 ft (or the shed setback, if that is larger). That usually leaves a comfortable yard between the two buildings. What limits you in practice is often lot coverage, building separation and utility connections, which cities still regulate the same way they do for houses. A narrow city lot may push the ADU over a garage or along an alley instead.

Steps before you build

1. Confirm your city or county is a subject jurisdiction, and read its updated ADU code. Many rewrote their codes around the June 30, 2025 deadline.
2. Ask how the city measures ADU size and where it draws the line (750 ft², 800 ft², a share of the house).
3. Check utilities: a separate water or sewer tap, and the fees for it, are still local decisions.
4. Draw the plan to scale. Most building departments accept homeowner drawings for a simple ADU; see how to draw floor plans for a building permit.
5. Compare with other states if you are deciding between markets; our ADU laws by state overview lists them. California's ADU size limits are the most generous in the country, and nearby Utah's detached ADU law and Montana's SB 528 set their own mandates.

What FloorGen checks

The template opens under FloorGen's IRC code profile, which checks every habitable room against the 70 ft² and 7 ft minimums, flags doors that swing into furniture and walkways narrower than about 30 in. It does not check zoning: setbacks, lot coverage, ADU size caps and parking are for you and your city. It does check ceiling heights and each bedroom's escape window, but not alarms.