Denver vs. Aurora ADU rules
Denver and Aurora sit at opposite ends of Colorado's ADU spectrum. Denver's CB24-1302 made ADUs a use by right citywide in December 2024 — no rezoning, no public hearing, and (since August 2025) no parking minimum — with footprint caps of 864 sq ft on smaller lots and 1,000 sq ft on larger ones. Aurora's code — UDO §146-3.3.6.G — still restricts ADUs to detached units under 650 sq ft in the Original Aurora subdistricts, requires an alley-accessed parking space, and routes every application through a Planning Commission public hearing; the state named Aurora non-compliant with Colorado's ADU law in October 2025.
✓ Verified against code · August 19, 2026
Denver rules run under Denver Zoning Code §11.8.2 and Article 3/5 form standards, adopted by CB24-1302 (amended by CB25-0684, CB25-2163), in effect since December 16, 2024.
✓ Verified against code · August 19, 2026
Aurora rules run under UDO §146-3.3.6.G (2018-era rules carried into the 2019 UDO), adopted by No HB24-1152 compliance ordinance exists, in effect since September 21, 2019.
Rule by rule
| Rule | Denver | Aurora |
|---|---|---|
| ADUs allowed per lot | One ADU per primary dwelling unit; in single-unit (SU) districts, one per zone lot, attached or detached. ADUs accessory to two-unit or multi-unit primaries must be detached.DZC §11.8.2.1.A.1–.2Previously: ADUs required a parcel-by-parcel rezoning through city council — changed by CB24-1302, effective Dec 16, 2024 | As codified: one detached ADU per single-family home — attached and internal ADUs prohibited — and only in the Original Aurora MU-OA subdistricts (OA-R1, OA-R2, OA-RMU) on alley-served lots, plus the Painted Prairie master-planned area under its own development plan. State law requires far more; the code hasn't caught up.UDO §146-3.3.6.G.1; Table 3.2-1; contrast C.R.S. 29-35-403(1) |
| Maximum size | SU districts: building footprint capped at 864 sq ft on lots of 7,000 sq ft or less, 1,000 sq ft on larger lots — footprint, not floor area, so a two-story unit can roughly double the space. Non-SU attached ADUs: up to the greater of 75% of the primary's floor area or 864 sq ft.DZC §11.8.2.1.B.2; §5.3.4.5 | 650 sq ft — below the 750 sq ft the statute protects, one of several provisions in apparent conflict with state law.UDO §146-3.3.6.G.1.h; contrast C.R.S. 29-35-402(18) |
| Detached ADU height | Urban contexts: 2 stories / 24 ft with a side-lot-line bulk plane (12 ft on lots ≤40 ft wide, then 45°). Suburban: 1 story/17 ft, or 2 stories/24 ft with a 20-ft rear setback. The ADU must sit in the rear 35% (urban) or 50% (suburban) of the lot.DZC §5.3.4.5 form tables | No taller than the principal dwelling, and never more than 24 ft.UDO §146-3.3.6.G.1.i, .p |
| Detached ADU setbacks | Urban: side 3 ft (lots ≤40 ft) or 5 ft; rear 5 ft without an alley — with an alley, 5 ft if garage doors face it, 0 ft if they don't. Suburban: side 3/5/7.5 ft by lot width; rear 10 ft (one story) or 20 ft (two). Vehicle access must come from the alley where one exists.DZC §5.3.4.5; §11.8.2.1.C.1 | Rear yard only; 5 ft side, 5 ft rear, 3 ft from the alley. An ADU atop an existing garage may keep the garage's setbacks.UDO §146-3.3.6.G.1.o; §146-4.2.3.F.1 |
| Off-street parking | None. Denver repealed all minimum vehicle parking requirements citywide effective August 11, 2025.CB25-0684; DZC Div. 10.4Previously: Minimum vehicle parking applied per zone — changed by CB25-0684, effective Aug 11, 2025 | One additional alley-accessed off-street space — and alley service is itself a prerequisite for the use. Both likely exceed what the statute permits.UDO §146-3.3.6.G.1.a, .k; contrast C.R.S. 29-35-403(2)(a), (3) |
| Owner-occupancy | No ongoing occupancy requirement. In SU districts, both units must stay under common ownership, and an owner must occupy the primary home at the time of permit application when adding an ADU to an existing house (waived for simultaneous new construction and DHA properties) — the exact carve-out state law allows.DZC §11.8.2.2.A–.B; C.R.S. 29-35-403(2)(b) | Still codified: the owner must occupy the primary dwelling or the ADU. Preempted on paper by state law since June 30, 2025, but not repealed.UDO §146-3.3.6.G.1.l; contrast C.R.S. 29-35-403(2)(b) |
| Lot coverage / floor area | A detached ADU counts toward the primary form table's maximum building coverage (Urban House: 60/45/40% by lot width). No ADU-specific bonus.DZC §5.3.4.5; Art. 5 form tables | Lot must exceed 6,000 sq ft; the ADU may cover no more than 50% of the rear yard, and 360 sq ft of usable private open space (minimum dimension 10 ft) must remain.UDO §146-3.3.6.G.1.e, .g |
| Permit path & timeline | Use by right citywide where single-unit dwellings are allowed — no rezoning since December 2024. Zoning permit + building permit + sewer use & drainage permit; a licensed contractor is required (homeowners can't self-permit). No fixed timeline — the city publishes only a live average-review-times dashboard.CB24-1302; Denver CPD ADU permits page | Conditional use with a Planning Commission public hearing — the opposite of the administrative approval state law mandates. No published timeline.UDO Table 3.2-1; contrast C.R.S. 29-35-403(1) |
Denver: worth knowing
- Carriage-lot ADUs are allowed without any primary dwelling — rare anywhere.
- The WDSF+ pilot (Denver Housing Authority / West Denver Renaissance Collaborative) offers design and finance support for income-restricted-rent ADUs, expanded citywide.
- Short-term renting an ADU requires the host to live in the primary structure (Denver's STR primary-residence rule).
- Denver is not on the state's certified ADU-supportive-jurisdiction list, so it doesn't participate in the HB24-1152 fee-reduction grant program.
- A rooftop deck up to 100 sq ft is allowed on alley-adjacent ADUs; no tiny-homes-on-wheels or RVs.
Denver: on our watchlist
The at-application owner-occupancy rule for existing-house ADUs draws ongoing criticism and is a likely future amendment target; nothing is filed after CB25-2163 (Feb 2026).
Aurora: worth knowing
- The numbers tell the story: 9 ADUs permitted (5 built) since 2018, while 262 inquiries between 2023 and mid-2026 fell outside the eligible zones.
- Council rejected the staff-drafted compliance ordinance on June 9, 2025 — the exact tally is contested (press reported 6–2 while admitting the clerk never announced it; a meeting-video summary says 7–2), so we publish the rejection without a number; a July 2026 study session directed staff to draft a broader fix (internal/attached/detached ADUs on most single-family lots, administrative review) — nothing adopted yet.
- Aurora is a plaintiff in the six-city home-rule lawsuit against the state, but that suit targets other housing laws (HB24-1313, HB24-1304, an executive order) — not the ADU statute itself.
- Aurora is not a state-certified ADU-supportive jurisdiction, which affects its access to related state grant programs.
- How the city treats an application citing state law directly (outside the MU-OA zones) is publicly unstated — the city's 2024 memo says existing requirements remain until the UDO is amended.
Aurora: on our watchlist
The corrective ordinance directed at the July 13, 2026 study session — this page goes materially stale the day it's adopted; it's the top item on our watchlist.
The six-city home-rule lawsuit (other housing statutes) remains pending and could reshape the preemption landscape.
Full detail: Denver · Aurora · back to the Colorado hub. Not legal advice — every fact above cites the code section it comes from; check the cite, or ask your city’s planning department to confirm your specific lot.