How big can a Fort Collins ADU be?
✓ Verified against code · August 19, 2026
For a new detached unit: 750 sq ft if your home is under 1,667 sq ft, otherwise the lesser of 1,000 sq ft or 45% of the home. Converting an existing outbuilding allows 800 sq ft, and basement ADUs can take the whole floor.
Citation: LUC §3.1.8
How current is this?
Fort Collins’s ADU rules run under Land Use Code §3.1.8 and zone-district standards (Ordinance 009-2025). After the 2022–23 land-use-code repeal saga, Fort Collins re-adopted its code in May 2024 and rewrote the ADU rules for state compliance effective February 14, 2025 (Ordinance 009-2025). The rules are clean and generous; the fees are the story — expect $20,000–25,000 all-in before construction. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Fort Collins ADU questions
- What does a Fort Collins ADU permit actually cost?
- Can I build an ADU anywhere in Fort Collins?
- Can I Airbnb a Fort Collins ADU?
All Fort Collins 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.