Centennial ADU rules
✓ Verified against code · August 20, 2026
Current rules under Land Development Code §12-3-603(H), adopted by Ordinance 2024-O-03, in effect since June 15, 2024. Centennial adopted its ADU ordinance in May 2024, a year before Colorado's June 30, 2025 deadline — and then did not revisit it. In October 2025 the state identified Centennial among roughly a dozen jurisdictions not complying with HB24-1152. Two provisions stand out: an unconditional parking requirement that matches none of the statute's three conditions, and a size formula tied to the principal dwelling's footprint with no floor at the 750 sq ft the statute protects. We checked Ordinance 2026-O-07, adopted June 2, 2026, directly: it amends sixteen provisions and none of them touch the ADU or parking sections.
Common questions, answered from the code
Is Centennial complying with Colorado's ADU law?
The state says no. In October 2025 Colorado's Department of Local Affairs identified Centennial among roughly a dozen jurisdictions not complying with HB24-1152, as part of a review tied to grant eligibility under the governor's executive order. Two provisions are the likely reasons: Centennial requires an off-street parking space unconditionally, where the statute permits a parking requirement only under three narrow conditions, and its size formula can fall below the 500 to 750 sq ft range the statute protects. We checked the city's June 2026 ordinance directly and it does not fix either provision.
DOLA October 2025 compliance review; LDC §12-3-603(H) · Permalink
How big can a Centennial ADU be?
There is no flat square-foot cap — the limit is the lesser of 50% of your house's footprint, or the total attic and basement area if you are not expanding the footprint. That means the answer depends entirely on your existing house, and on a small home the formula can produce a cap below the 500 to 750 sq ft that state law is supposed to protect.
LDC §12-3-603(H)(5)(a) · Permalink
Do I need parking for a Centennial ADU?
Yes — one off-street space in addition to your principal dwelling's spaces, with no conditions attached. This is one of the provisions that puts Centennial at odds with state law, which allows a city to require a new space only when there is no existing usable off-street space, the zone required parking as of January 2024, and on-street parking is barred on the block. Centennial's requirement applies regardless.
LDC §12-3-603(H), (F)(2) · Permalink
Do I have to live on the property in Centennial?
No, there is no occupancy requirement at any point. But if you will not live in either unit, you must register the ADU — paying a fee and sending certified-mail notice to adjacent neighbours — and renew that registration annually with fresh notice each year. Whether an annually renewing obligation is the kind of ongoing requirement HB24-1152 bars is an open question no source we found resolves.
LDC §12-3-603(H)(8) · Permalink
How tall can a detached Centennial ADU be?
17 ft, which is among the lowest detached ADU height limits in this ledger and effectively rules out a two-storey backyard unit. An attached ADU instead takes your zone district's maximum height for the principal dwelling.
LDC §12-3-603(H)(5)(c)(ii)–(iii) · Permalink
The rules at a glance
| ADUs allowed per lot | One per lot. The code draws no distinction between attached, detached and interior units — all count against the same single-unit cap — and the lot must have a single-family principal dwelling, built or under concurrent construction.LDC §12-2-302(a); §12-3-603(H)(2)(b)–(c) |
| Maximum size | No flat square-foot cap. The limit is the lesser of 50% of the principal dwelling's footprint, or the total attic and basement area including the stairwell where no footprint-expanding construction is involved. On a small house that formula can land below the 500–750 sq ft range the statute protects.LDC §12-3-603(H)(5)(a); contrast C.R.S. 29-35-402(18) |
| Detached ADU height | 17 ft for a detached ADU. An attached ADU takes the principal dwelling's zone-district maximum.LDC §12-3-603(H)(5)(c)(ii)–(iii) |
| Detached ADU setbacks | No ADU-specific reduction — an ADU must meet the principal dwelling's setback and building-coverage standards for the zone. There is no alley exception; the alley reference in the zoning table is an access requirement in Limited Use zones, not a setback allowance.LDC §12-3-603(H)(5)(c)(i); Table 12-2-401 |
| Off-street parking | One off-street space, unconditionally, in addition to the principal dwelling's spaces. The city states it plainly: "The ADU shall provide one off-street parking space in addition to the spaces required for the principal dwelling." That is not conditioned on any of the three tests the statute allows.LDC §12-3-603(H), (F)(2); contrast C.R.S. 29-35-403(3) |
| Owner-occupancy | No occupancy mandate at any point, including at application. But an owner who will not occupy either unit must register: a fee, certified-mail notice to adjacent neighbours, and annual renewal with fresh notice each year. Whether an annually renewing registration amounts to the ongoing requirement the statute bars is unresolved.LDC §12-3-603(H)(8); contrast C.R.S. 29-35-403(2)(b) |
| Lot coverage / floor area | Centennial uses building coverage rather than floor-area ratio, and ADUs count toward it: all accessory buildings are included in the calculation, with no ADU exemption.LDC §12-3-603(A) |
| Permit path & timeline | Administrative and by-right, with no public hearing — the zoning tables show ADUs as permitted or limited uses in every residential zone, never conditional. A pre-submittal meeting is required. No published review timeline.LDC §12-3-603(H)(3); Tables 12-2-302, 12-2-401 |
Worth knowing
- Short-term rentals are not allowed in ADUs — a restriction HB24-1152 expressly permits a city to keep.
- An ADU cannot be sold or subdivided separately from the principal dwelling.
- Attached ADUs are exempt from the fiber-conduit requirement that otherwise applies (§12-11-305).
- There is no citywide tap-fee waiver; tap fees vary by water district.
- ADUs are allowed in planned unit developments unless the specific PUD prohibits them — a carve-out independent analysts have flagged as another restriction beyond what the statute contemplates.
- An owner who does not live in either unit must register the ADU and renew that registration every year, re-notifying adjacent neighbours each time.
On our watchlist
The October 2025 non-compliance finding is documented through named journalism quoting the DOLA director and an explicit list from the governor's office, not through a published DOLA compliance report we could retrieve. The state's own compliance dashboard is not machine-readable.
No council packet, hearing notice or press release describing a compliance-fix ordinance was found. An unpublicised effort cannot be ruled out.
Ordinances 2025-O-06 and 2025-O-12 are described as definitional amendments by a third-party aggregator; we have not read their primary text.
Primary sources
- Ordinance 2024-O-03 (adopting ordinance, full text)
- City of Centennial — Accessory Dwelling Units
- Colorado DOLA — Accessory Dwelling Units (HB24-1152)
Other Colorado cities
Arvada · Aurora · Boulder · Broomfield · Castle Rock · Colorado Springs · Denver · Fort Collins · Greeley · Lakewood · Longmont · Loveland · Pueblo · Thornton · Westminster
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. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.