How big can an ADU be in Colorado?
✓ Verified against code · August 19, 2026
Size caps vary widely by city, but Colorado's ADU statute requires every city to allow an ADU somewhere in the 500 to 750 sq ft range at minimum. Lakewood has the most generous flat cap on the Front Range at 1,400 sq ft, up from 700 sq ft before its 2024 compliance amendment. Denver caps footprint, not floor area, at 864 sq ft on smaller lots or 1,000 sq ft on larger ones, so a two-story ADU can roughly double the livable space. Boulder's detached cap is a tighter 800 sq ft. Arvada's smallest-lot tier, 600 sq ft, sits below the state's protected range.
Citation: varies by city — see city pages
How current is this?
Colorado’s ADU rules run under HB24-1152 (2024). HB24-1152 (codified at C.R.S. 29-35-401 through 29-35-405) required every Colorado city or town of 1,000+ residents inside a metropolitan planning organization to allow one ADU wherever a single-family home is allowed, through administrative approval, by June 30, 2025 — banning ongoing owner-occupancy mandates (an at-application residency check is allowed), most new-parking requirements, and design standards that would block an ADU in the 500–750 sq ft range. Note the contrast with Washington: one ADU per lot, not two. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Colorado ADU questions
- What is HB24-1152?
- Which Colorado cities are not complying with the ADU law?
- Does Colorado allow two ADUs per lot?
- What happened to Lakewood's zoning code?
- What is the 500 to 750 square foot size protection in Colorado's ADU law?
- Do Colorado cities require ADU owners to live on the property?
- Can Colorado cities require parking for an ADU?
- What does home rule mean for Colorado's ADU law?
- What do Colorado ADU permits cost?
- How long does it take to get an ADU permit approved in Colorado?
- Can I rent out my Colorado ADU short-term on Airbnb?
Not legal advice — local ordinances can go further than the state floor. The citation above points at the governing statute; check your city’s code for the specifics.