Colorado's HB 24-1175: ADU Reform in 2024
Colorado became the most recent major state to pass comprehensive ADU reform when Governor Polis signed House Bill 24-1175 into law on August 7, 2024. HB 24-1175 is Colorado's first dedicated ADU legislation — a direct codification of best practices seen in California, Oregon, and Washington, tailored for Colorado's growth landscape. Colorado's housing market has been under enormous pressure. The Denver metro area has seen home price appreciation exceeding 50 percent over five years. Resort communities like Telluride, Aspen, and Breckenridge face acute workforce housing shortages. College towns like Fort Collins, Boulder, and Greeley struggle with student housing demand. HB 24-1175 was designed to unlock existing single-family lots as housing production sites without new infrastructure investment. The law's core provisions are clear. It requires all Colorado municipalities with a population of more than 1,000 to allow at least one ADU per single-family residential lot by-right. Ministerial approval is required — no discretionary design review for ADUs meeting objective standards. Owner-occupancy requirements are prohibited as a condition of ADU approval. The law limits parking requirements for ADUs: no additional parking is required for ADUs within 0.25 miles of a high-frequency transit stop. A state enforcement mechanism was created through the Colorado Department of Local Affairs (DOLA) — cities that fail to update their codes face state intervention. Local code compliance was required by July 1, 2025. Colorado's reform was paired with HB 24-1174, a companion 'missing middle housing' bill requiring cities with 5,000 or more population to allow at least 2 units per single-family lot. Together, the two bills significantly expand Colorado housing options. Municipalities that had previously blocked ADU development through minimum lot size requirements, owner-occupancy mandates, or excessive parking requirements are now required to change their codes.
Denver ADU Rules: Colorado's Most Developed ADU Market
Denver had an ADU ordinance in place before HB 24-1175 passed — the city updated its ADU framework in 2021, eliminating its owner-occupancy requirement and reducing parking mandates. Denver's existing framework already aligned with most of what HB 24-1175 requires, making Denver one of the smoother compliance cases when the state law took effect. Denver regulates ADUs under the Denver Zoning Code (DZC), administered by Community Planning and Development (CPD). Denver does not use the California JADU concept. The maximum size for both detached and attached ADUs in Denver is generally 1,000 square feet, consistent with HB 24-1175. ADU floor area may also be limited to 50 percent of the primary dwelling's floor area in some zones — check your specific zone designation in the Denver Zoning Code Article 4. Maximum ADU height in Denver is typically 24 feet for detached ADUs, supporting two-story backyard cottages. Attached ADUs follow the zone's primary dwelling height standard. Setbacks for detached ADUs are 5 feet from side and rear property lines. Denver allows alley access for ADUs where alleys exist — alley-accessed ADUs in Denver's older grid neighborhoods (Capitol Hill, Sunnyside, Whittier, Highlands) are a particularly efficient placement because they don't require a driveway. Denver's single-unit residential zones — E-SU-A through E-SU-D (Edge, suburban character) and U-SU-A through U-SU-C (Urban, denser character) — cover most of Denver's single-family neighborhoods. Denver also has two-unit zones (U-TU-A, U-TU-B, U-TU-C) that allow duplexes by right, and ADUs may be permitted on top of two-unit uses in some configurations. Denver's historic districts — Swansea, Curtis Park, Potter-Robbins, Capitol Hill — require Design Review before ADU permits are issued for properties within historic overlay zones or individually designated landmarks.
What You Can Build in Colorado
Colorado homeowners in municipalities covered by HB 24-1175 — essentially any incorporated city or town over 1,000 population — have a clear right to build at least one ADU on their single-family lot. Understanding the options available helps you choose the right ADU type for your situation. Detached ADUs in Denver and most Colorado cities are standalone structures in the rear yard, generally up to 1,000 square feet and up to 24 feet in height. Detached ADUs require 5-foot setbacks from side and rear property lines in Denver's standard residential zones. The rear yard of most Denver lots — especially in the dense urban grid neighborhoods — has enough space for a 600-800 square foot detached ADU without feeling cramped. Attached ADUs are units attached to the primary dwelling, up to 1,000 square feet in most Denver zones. Common configurations include a basement apartment with a separate exterior entrance, a side or rear addition, or a main-floor conversion of living space with a separate entrance. Garage conversions — converting a detached or attached garage into living space — are permitted as either attached or detached ADUs depending on garage configuration. This is often the most cost-effective ADU option in Denver's older grid neighborhoods, where detached garages are common. Colorado law does not include California's JADU concept (units within existing structures up to 500 sqft with shared utilities). However, interior conversions — finishing a basement as a separate apartment — accomplish similar goals and are permitted in Denver as attached ADUs. HB 24-1175 sets a floor of 1 ADU per lot statewide, but Denver's local ordinance may allow 1 additional ADU in certain zones. Two-unit zones (U-TU) by definition allow 2 primary units and may allow additional ADUs. Consult Denver CPD for zone-specific maximums beyond the state minimum.
Permit Process and Costs in Denver
Denver ADU permits are processed by Community Planning and Development (CPD). The permit process is ministerial under HB 24-1175 — CPD cannot exercise discretion for ADUs meeting objective standards. HB 24-1175 requires ministerial approval within 60 days for compliant applications. Denver CPD typically processes standard ADU permits in 4-8 weeks. Denver offers expedited review for ADUs meeting pre-approved design standards. Plan check fees in Denver typically run $1,500 to $4,500 depending on project value. Building permit fees run $1,200 to $3,500. Total base permit fees for a standard Denver ADU project typically range from $3,000 to $10,000 — a meaningful range driven primarily by project valuation. In addition to base permit fees, Denver Public Schools impact fees may apply for new residential units including ADUs. DPS impact fees are approximately $3,000 to $6,000 for new residential units — verify current rates with CPD before budgeting. Denver infrastructure use fees (IUF) may also apply depending on project type and location. Total permit and impact fees for a new detached ADU in Denver can therefore reach $6,000 to $16,000 when school impact fees are included. For garage conversions and interior attached ADUs (no new exterior construction), fees are generally at the lower end of this range. Denver's construction costs reflect a mountain West premium. A new detached ADU in Denver typically runs $120,000 to $280,000 for construction. Garage conversions and basement conversions are less expensive: often $50,000 to $100,000. Total all-in costs (design, permits, construction) for a new detached ADU in Denver typically run $150,000 to $350,000. Denver has a growing ADU specialist contractor ecosystem — professionals who have navigated the Denver CPD process repeatedly and can streamline your project.
How Colorado Compares to Other Western States
Colorado's HB 24-1175 (2024) joins California, Oregon, and Washington as states with comprehensive statewide ADU reform. Understanding how Colorado's law compares to its neighbors helps homeowners and investors calibrate expectations. California (since 2019-2020): the most comprehensive ADU law, with explicit size limits (up to 1,200 sqft detached), 4-foot setbacks, full impact fee waivers under 750 sqft, and the unique JADU concept for interior conversions up to 500 sqft. California's preemption is the most detailed and most tested in court. Colorado's HB 24-1175 mirrors California's approach but without some of California's specific provisions (no impact fee waiver mandate, no JADU concept, no 4-foot setback standard). Oregon (since 2019): HB 2001 eliminated single-family-only zoning and requires middle housing, creating permissiveness through land use reform rather than ADU-specific regulation. Portland caps detached ADUs at 800 sqft, smaller than Denver's typical 1,000 sqft limit. Oregon has a lot split law (SB 458 for middle housing); Colorado does not. Washington (since 2023): HB 1337 explicitly allows 2 ADUs per lot statewide, a provision Colorado's law does not include (HB 24-1175 requires at least 1 ADU per lot). Seattle's 1,000 sqft size limit matches Denver's typical cap. Both states prohibit owner-occupancy requirements. Texas (no state law): Texas has no statewide ADU law. Austin has its own permissive ADU ordinance under Title 25 of the development code, but Dallas, Houston, and San Antonio each have different local rules. Colorado is significantly more permissive than Texas cities for ADU development under statewide law. Colorado is well-positioned for future ADU legislation. HB 24-1175 was paired with HB 24-1174 (middle housing), and advocates are pushing for additional provisions in future sessions — including potential requirements for lot splits, impact fee caps, and expanded two-ADU-per-lot allowances similar to Washington's HB 1337.
Recent Changes: Colorado's ADU Legislative Timeline
Colorado's ADU law is the newest of the major state frameworks, having taken effect in August 2024. Here is the full context of where HB 24-1175 came from and where it may be heading. Pre-2024: Colorado had no statewide ADU law. Local cities including Denver, Boulder, and Fort Collins had their own ADU ordinances of varying permissiveness. Denver updated its ADU ordinance in 2021 to eliminate owner-occupancy requirements and reduce parking mandates. Boulder had a permissive ADU framework. Many smaller Colorado cities and towns had ADU restrictions or bans that HB 24-1175 would later preempt. HB 24-1175 (2024): signed into law August 7, 2024. Requires municipalities over 1,000 population to allow at least one ADU per single-family lot by-right. Ministerial approval required within 60 days. No owner-occupancy requirements allowed. Parking requirements limited near transit. State enforcement through DOLA. Local code compliance required by July 1, 2025. HB 24-1174 (2024): companion bill requiring cities with 5,000 or more population to allow at least 2 units per single-family lot — the 'missing middle housing' companion to the ADU bill. Together, these two 2024 bills significantly expand housing options statewide. Denver compliance (2024-2025): Denver's existing ADU ordinance largely aligned with HB 24-1175 requirements, requiring relatively modest code updates. Denver CPD updated its ADU guidance materials and verified code compliance by mid-2025. Other Colorado cities: cities and towns that previously banned or heavily restricted ADUs were required to update their codes by July 1, 2025. DOLA has oversight authority over non-compliant jurisdictions. Future potential: Colorado advocates are pushing for future legislation to require 2 ADUs per lot (like Washington), add impact fee caps (like California), and create a lot split mechanism (like California's SB 9 or Oregon's SB 458). Watch Colorado legislative sessions for ADU-related bills.
Getting Started with a Colorado ADU
Planning an ADU in Colorado under the new HB 24-1175 framework is a clear process for most homeowners. Here is the recommended sequence. Step 1: Confirm your municipality is covered by HB 24-1175. All Colorado municipalities with population over 1,000 are covered. This includes Denver, Colorado Springs, Aurora, Fort Collins, Boulder, Pueblo, and the vast majority of incorporated Colorado cities and towns. Rural unincorporated areas may have different standards — confirm with your county. Step 2: Look up your city's local ADU code. In Denver, consult the Denver Zoning Code (DZC) Article 4 for your zone designation. Denver CPD maintains ADU resources at its city website. Other Colorado cities updated their local codes by July 1, 2025 — use PropertyZoned's city pages as a starting point. Step 3: Identify your zone designation. Denver's zone system (E-SU for edge suburban, U-SU for urban single-unit, U-TU for urban two-unit) affects setback standards, height limits, and specific ADU allowances. Your zone designation is visible on Denver's online zoning map at the CPD website. Step 4: Use PropertyZoned's ADU Feasibility Checker. Enter Denver (or your Colorado city), lot size, and zone to get a preliminary assessment of what you can build based on your city's rules. Step 5: Evaluate garage conversion potential. Denver's older grid neighborhoods have many detached garages accessible from alleys — ideal for conversion to ADUs at lower cost than new construction. Assess whether your garage qualifies before budgeting for new construction. Step 6: Budget for school impact fees. In Denver, add $3,000 to $6,000 for DPS school impact fees on new ADUs to your permit cost estimate. Verify current rates with CPD. Step 7: Hire a Denver-familiar architect and apply for permits. Denver CPD typically processes standard ADU permits in 4-8 weeks. Properties in historic overlay zones require Design Review — allow additional time. Colorado's ADU environment is newly permissive and still maturing. Homeowners who move early have an advantage in markets where ADU awareness among builders and designers is growing rapidly.
Frequently Asked Questions
When did Colorado's ADU law (HB 24-1175) take effect?
Colorado HB 24-1175 was signed into law August 7, 2024, and took effect immediately. Colorado municipalities with population over 1,000 were required to update their local development codes to comply by July 1, 2025. Denver's existing ADU ordinance already largely aligned with HB 24-1175 requirements.
Can Colorado cities ban ADUs under HB 24-1175?
No. HB 24-1175 requires all Colorado municipalities with population over 1,000 to allow at least one ADU per single-family lot by-right. Cities cannot ban ADUs, require owner-occupancy, or impose minimum lot sizes specifically targeting ADU prohibition. The Colorado Department of Local Affairs (DOLA) has enforcement authority over non-compliant jurisdictions.
What is the maximum ADU size in Denver?
Denver typically allows detached and attached ADUs up to 1,000 square feet. ADU floor area may also be limited to 50% of the primary dwelling's floor area in some zone designations. Check your specific zone designation in the Denver Zoning Code Article 4 or consult Denver CPD.
Can I build 2 ADUs on my Denver lot?
HB 24-1175 sets a minimum of 1 ADU per lot statewide. Denver's local ordinance may allow 1 additional ADU in certain zone designations. Two-unit zones (U-TU series) allow 2 primary units by right and may allow additional ADUs. Washington State allows 2 ADUs per lot by right under HB 1337 — Colorado has not yet reached this level of allowance statewide. Confirm with Denver CPD for your specific zone.