Thinking about adding a backyard suite or renting out your basement in Castle Pines? With Colorado’s new ADU law, the rules are changing and the opportunity is real. You want clarity on what is allowed, how HOAs fit in, and what this could mean for your home’s value. In this guide, you’ll learn what the state requires, what Castle Pines must do, and how to move forward with confidence.
Let’s dive in.
Colorado’s new ADU law, in plain English
Colorado passed House Bill 24-1152 to make it easier to build accessory dwelling units, or ADUs. The law requires many cities, including Castle Pines, to allow one ADU on lots with a single-unit detached home and to approve ADUs through an administrative process without a public hearing. You can review the bill details on the Colorado General Assembly’s page for HB24-1152.
Under the statute, local governments have limits on what they can require. In most cases they cannot mandate new off-street parking or owner-occupancy, and they cannot add restrictive design standards that go beyond what they already require for single-unit homes. The statute spells out what is allowed, including objective rules for safety and compatibility, in C.R.S. 29-35-403.
Key dates to know
- May 13, 2024: HB24-1152 was signed into law.
- June 30, 2025: Jurisdictions had to submit an ADU compliance report to the state.
- August 1, 2025: DOLA launched an ADU grant program to support implementation and homeowners. See the DOLA ADU guidance and toolkit.
- October 6, 2025: A governor’s action tied some state funding to compliance with new housing laws, which raised the stakes for cities. Read the governor’s release on state actions to increase housing supply.
What this means in Castle Pines
Castle Pines is a “subject jurisdiction,” which means the state ADU requirements apply here. The City must allow one ADU as an accessory use to a single-unit detached home and approve applications administratively using objective standards. DOLA’s ADU page tracks guidance and program details for subject jurisdictions like Castle Pines in its ADU resources.
City planning is updating local land-use rules, and you can watch for changes on the City’s Zoning and ULDC page. As of fall 2025, news coverage listed Castle Pines among communities reported as not compliant with the law, which may change as the City updates its code. You can see that coverage in this Colorado Politics report.
Changes you can expect locally
- Allow ADUs as an accessory use to single-unit homes, including internal, attached, and detached forms.
- Provide an administrative permit path that uses objective standards without a public hearing.
- Remove rules that require new off-street parking or owner-occupancy, and avoid design limits that are more restrictive than for the main home.
- Update treatment of PUDs and plats so they do not block ADUs beyond what base zoning allows.
- Submit required compliance reporting to the state. See the statute for details in C.R.S. 29-35-403.
ADU types and rules you can expect
You will likely see three ADU types permitted: internal conversions (like basements or space above a garage), attached additions, and detached backyard cottages. The state sets a baseline for permission, and the City can still apply objective rules for setbacks, height, lot coverage, and architectural compatibility.
Building and fire codes still matter. Expect full building permits, inspections, and compliance for electrical, plumbing, and mechanical systems. In some areas, fire access, wildland-urban interface rules, or water and sewer capacity can affect feasibility. The statute allows these safety and capacity checks under C.R.S. 29-35-403.
Parking, owner occupancy, and HOAs
State law generally prevents cities from requiring new off-street parking for ADUs and from mandating owner occupancy. There are narrow exceptions, but the default is less restrictive to help ADUs move forward. The specific language is in C.R.S. 29-35-403.
For HOAs, Colorado updated CCIOA so associations cannot flatly prohibit ADUs where zoning allows them. HOAs can still adopt reasonable, objective restrictions that do not effectively block an ADU. Review the HOA statute at C.R.S. 38-33.3-106.5.
Buying or selling a home with an ADU
If you plan to sell, an ADU can increase flexibility and market appeal. Be sure the unit is permitted and up to code. Unpermitted living spaces can cause title, insurance, appraisal, and buyer financing issues. Confirm the permits and certificate of occupancy with the City.
If you plan to buy, verify whether any existing ADU was permitted and finaled, and ask about any HOA covenants or PUD rules that could affect future changes. For all parties, remember that short-term rental rules remain local. DOLA’s summary confirms that cities still regulate STR use, so check local policy in the DOLA ADU guidance.
How to move forward in Castle Pines
Use this quick checklist before you design or write an offer:
- Check City code updates and objective ADU standards on the Zoning and ULDC page.
- Verify permits or past inspections for any existing or former ADU. Start with the City’s Ordinances and Resolutions page for department contacts.
- Review your HOA declaration and design rules. Use the state HOA statute to understand limits on enforcement: C.R.S. 38-33.3-106.5.
- Confirm objective standards and safety rules that apply to your lot, including setbacks, height, WUI, fire access, and utility capacity. The state framework is in C.R.S. 29-35-403.
- Explore state guidance and potential ADU grants through DOLA’s ADU resources.
Funding and incentives snapshot
The state launched an ADU grant program in 2025 through DOLA, with implementation support and financing tools. The program details and timelines are posted in the DOLA ADU guidance and toolkit. If you plan to build, check those materials for eligibility and timing before you finalize plans.
Common pitfalls to avoid
- Do not assume every lot can fit a detached ADU. Confirm objective local standards and safety rules first.
- Do not start work without permits. Unpermitted units can create expensive problems at resale.
- Do not ignore HOA design rules. They cannot prohibit ADUs outright where allowed, but they can set reasonable standards.
- Do not presume short-term rentals are allowed. Check local rules before advertising a nightly rental.
Ready to assess whether an ADU makes sense for your Castle Pines property or your next purchase? Let our team help you weigh value, timing, and next steps. Reach out to The Denver Trio for a clear game plan tailored to your goals.
FAQs
What is an ADU under Colorado law?
- An ADU is a secondary home on the same lot as a single-unit house. It can be internal, attached, or detached, and must meet objective local building and safety standards under C.R.S. 29-35-403.
Are ADUs allowed in Castle Pines right now?
- State law requires Castle Pines to allow one ADU per qualifying lot and to approve it administratively. The City is updating local rules, and fall 2025 coverage listed Castle Pines as not yet compliant. Check the City’s zoning page and DOLA’s ADU resources for current status: Zoning and ULDC and DOLA ADU guidance. See reporting from Colorado Politics.
Do I need to add parking for an ADU in Castle Pines?
- Generally no. The state bars cities from requiring new off-street parking for ADUs in most cases, with narrow exceptions detailed in C.R.S. 29-35-403.
Can my HOA stop me from building an ADU in Castle Pines?
- Not outright if zoning allows it. HOAs can adopt reasonable, objective restrictions but cannot effectively prohibit ADUs under C.R.S. 38-33.3-106.5.
Can I use my ADU for short-term rentals in Castle Pines?
- It depends on local rules. The state law does not force cities to allow short-term rentals, so check Castle Pines policies and DOLA’s overview in the ADU guidance.
What permits do I need to build an ADU in Castle Pines?
- You will need building permits and inspections for structural, electrical, plumbing, and mechanical work. Contact the City using the information on the Ordinances and Resolutions page.
How long will ADU approval take in Castle Pines?
- State law requires an administrative process without a public hearing, which should be more predictable. Actual timelines depend on City staffing and standards, so start with planning on the Zoning and ULDC page and review the state framework in C.R.S. 29-35-403.
