ADU Rules: Austin vs Denver (2026 Comparison)
Compare ADU regulations, permit fees, size limits, and timelines between Austin TX and Denver CO. No state law in Texas vs Colorado's HB 24-1152 preemption.
Side-by-Side Comparison
Austin vs Denver
| AustinTX | DenverCO | |
|---|---|---|
| ADUs Allowed? | Yes (local code — no state law) | Yes, by right (CO HB 24-1152, 2024) |
| Max Detached ADU Size | 1,100 sq ft or 0.15 FAR, whichever is greater | 1,000 sq ft (or 50% of primary dwelling) |
| Max Attached ADU Size | No greater than main house floor area | 1,000 sq ft |
| Parking Required? | 1 space per ADU unless within 0.25 mile of CapMetro urban rail | None within 0.25 miles of high-frequency transit; reduced citywide |
| Owner Occupancy Required? | No | No (CO HB 24-1152 prohibits) |
| State Preemption? | No (Texas has no statewide ADU law) | Yes (Colorado HB 24-1152, signed May 13, 2024) |
| Estimated Permit Fees | $3,000–$15,000 including impact fees | $3,000–$10,000 in permit fees; school fees may add $3,000–$6,000 |
| Permit Timeline | 2-4 months plan review | 4-8 weeks; ministerial (administrative) approval under state law, see official source for current statutory detail |
| Ministerial Approval? | No (Austin uses discretionary review for some elements) | Yes (CO HB 24-1152 requires ministerial approval, no discretionary design review) |
Key Differences
Austin and Denver represent two fundamentally different ADU regulatory frameworks. Denver operates under Colorado's HB 24-1152 (signed May 13, 2024; local compliance required by July 1, 2025), which mandates by-right ADU approval throughout the state and requires ministerial review (no discretionary denial). Austin, by contrast, operates solely under local code with no state ADU law backing it — Texas has not enacted ADU preemption as of 2026. This matters in practice. Denver's state preemption means property owners have a legal right to build a conforming ADU, and the city cannot deny applications that meet objective standards. Austin's purely local ADU rules (under the HOME Ordinance and Title 25 Development Code) are generally permissive, but lack the legal backstop of state preemption. Austin's HOME Ordinance (2023) goes further in a different direction, allowing up to 3 total units on any residential lot — more than Denver's state minimum of 1 ADU per lot. Austin's review timeline is notably longer (2-4 months) compared to Denver's typical 4-8 week processing time. Austin's impact fees — including water/wastewater charges of $3,000–$8,000 — add cost variability. Denver's school impact fees ($3,000–$6,000) are significant but more predictable.
Cost Comparison
ADU permit fees in Austin range from $3,000–$15,000 including impact fees (water/wastewater fees and transportation fees vary by location). Austin's impervious cover limits (especially in Barton Springs watershed) can constrain what's buildable. Denver ADU permit fees are $3,000–$10,000 in basic fees. School district impact fees apply. Denver lacks Austin's watershed-based impervious cover restrictions, making lot coverage calculations more straightforward in most neighborhoods. ADU construction costs vary by design, contractor, and site conditions. For current fee schedules, see Austin Development Services Department (austintexas.gov/department/development-services) and Denver Community Planning and Development (denvergov.org/cpd).
Our Verdict
Denver has the edge for regulatory predictability thanks to Colorado's HB 24-1152 preemption — you have a legal right to build a conforming ADU through an administrative (ministerial) approval process. Austin is competitive on unit density (up to 3 total units under HOME) and has good ADU infrastructure, but the longer review timeline (2-4 months) and lack of state backing can create uncertainty. For investors building an ADU for rental income, Denver's ministerial approval certainty is valuable. For homeowners wanting maximum unit count flexibility, Austin's HOME Ordinance is the winner.
Explore Each City
Frequently Asked Questions
Does Texas have a statewide ADU law like Colorado?
No. Texas has not enacted statewide ADU preemption as of 2026. Austin's ADU rules come entirely from local code (Title 25 and the HOME Ordinance). Colorado's HB 24-1152 (signed May 13, 2024) requires all Colorado cities to allow at least 1 ADU per residential lot by right.
How many units can I build on one lot in Austin vs Denver?
Austin's HOME Ordinance (2023) allows up to 3 total units on any single-family lot citywide. Denver allows 1 ADU per lot under Colorado state minimum; local Denver ordinance may allow more in certain zones. Austin offers more total unit flexibility.
Is Austin or Denver more expensive for ADU permits?
Both are in the $3,000–$15,000 range for total government fees, but Austin's water/wastewater impact fees ($3,000–$8,000) can push costs higher. Denver's school impact fees ($3,000–$6,000) are significant. Both are less expensive than California cities in total fee burden.
Do I need a parking space for my ADU in Austin or Denver?
Austin requires 1 parking space per ADU unless the property is within 0.25 miles of a CapMetro urban rail station. Denver eliminated parking requirements for ADUs within 0.25 miles of high-frequency transit, and has reduced requirements citywide under Colorado HB 24-1152.
Source: PropertyZoned Editorial Research. Last verified April 5, 2026.