How tall can a detached Thornton ADU be?
✓ Verified against code · August 19, 2026
Genuinely ambiguous in the current tables: 35 ft clearly covers ADUs above garages, while other accessory structures cap at 16 ft — and a ground-level detached ADU sits between the definitions. Ask the city for a written determination before designing; we track this on our watchlist.
Citation: Table 18-76.1 fn 7
How current is this?
Thornton’s ADU rules run under Development Code §18-339 (reenacted Chapter 18) (Ordinance 3742). Thornton reenacted its entire Development Code effective September 1, 2025 — mostly statute-shaped, with one glaring exception: it kept an ongoing owner-occupancy requirement enforced by a recorded deed restriction, which Colorado's ADU statute has barred for cities like Thornton since June 30, 2025. The state's October 2025 compliance review listed Thornton among the non-complying jurisdictions. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Thornton ADU questions
- Does Thornton still require me to live on the property?
- How big can a Thornton ADU be?
- Do I need parking for a Thornton ADU?
- Does Thornton verify utility capacity for ADUs?
All Thornton 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.