How big can a Centennial ADU be?
✓ Verified against code · August 20, 2026
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.
Citation: LDC §12-3-603(H)(5)(a)
How current is this?
Centennial’s ADU rules run under Land Development Code §12-3-603(H) (Ordinance 2024-O-03). 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. We verified this answer against primary sources on August 20, 2026, and every change we catch is logged in the changelog.
More Centennial ADU questions
- Is Centennial complying with Colorado's ADU law?
- Do I need parking for a Centennial ADU?
- Do I have to live on the property in Centennial?
- How tall can a detached Centennial ADU be?
All Centennial ADU rules → · Compare Colorado cities →
Not legal advice — lot-specific overlays can change the answer for your parcel. The citation above points at the governing code section; check it, or ask the city to confirm.