Fort Collins ADU rules
✓ Verified against code · August 19, 2026
Current rules under Land Use Code §3.1.8 and zone-district standards, adopted by Ordinance 009-2025, in effect since February 14, 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.
Common questions, answered from the code
What does a Fort Collins ADU permit actually cost?
More than anywhere nearby: the Basic Development Review flat fee alone is $6,925, and the city's own guidance puts typical total fees — review, impact, utilities — at $20,000–25,000 before construction. Budget for it up front.
City ADU page · Permalink
Can I build an ADU anywhere in Fort Collins?
Nearly — since February 2025, ADUs are allowed in every zone district where a house, duplex, or triplex is allowed on the lot, through a staff-level review. The one hard geographic no: the Poudre River 100-year floodplain.
LUC Art. 2; §4.3.1(B) · Permalink
How big can a Fort Collins ADU be?
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.
LUC §3.1.8 · Permalink
Can I Airbnb a Fort Collins ADU?
Not if it was permitted on or after January 1, 2024 — new ADUs can't be short-term rentals; only earlier STR licenses are grandfathered.
LUC §4.3.1(B)(1) · Permalink
The rules at a glance
| ADUs allowed per lot | One ADU per lot — attached or detached — accessory to a detached house, duplex, triplex, or mobile home, in every zone district since February 2025.LUC §3.1.8; Art. 2 zone tables |
| Maximum size | New detached: 750 sq ft if the home is under 1,667 sq ft, otherwise the lesser of 1,000 sq ft or 45% of the home. Converting an existing legal accessory structure: 800 sq ft. Attached: the greater of 750 sq ft or 45% (basement ADUs: up to the full floor).LUC §3.1.8 floor-area tables |
| Detached ADU height | 1.5 stories / 28 ft, or the zone standard — Old Town caps at 24 ft or the house's height, whichever is less.LUC §3.1.8; §2.1.6 |
| Detached ADU setbacks | At least 5 ft from the house and 10 ft behind its front wall; side and rear per zone (RL example: side 5 ft, rear 15 ft — dropping to 5 ft along an alley).LUC §3.1.8; §2.1.4 |
| Off-street parking | None for the ADU — only the home's own minimums apply, and a tandem space can count.LUC Div. 5.9; city ADU page |
| Owner-occupancy | None — no owner-occupancy language anywhere in the code.LUC (verified absence); C.R.S. 29-35-403(2)(b) |
| Lot coverage / floor area | ADU floor area is excluded from Old Town's rear-lot floor-area caps and from the RL district's minimum-lot-area ratio — deliberate carve-outs that keep ADUs from eating the lot budget.LUC §2.1.6; §2.1.4 |
| Permit path & timeline | Basic Development Review — a staff decision — in every zone, then a building permit; a free conceptual design review is offered first. The BDR flat fee is $6,925, and the city itself pegs typical total fees at $20,000–25,000. No published day-count for review.LUC Div. 4.2; city ADU page |
Worth knowing
- The fee reality is the headline: $6,925 flat for review plus impact and utility fees lands most projects at $20,000–25,000 in fees before a shovel turns.
- ADUs permitted on or after January 1, 2024 may not be short-term rentals (earlier licenses grandfathered).
- No new dwelling units in the Poudre River 100-year floodplain.
- The lot under a home and ADU can't be split, but a condo plat is allowed.
- The ADU needs its own electric meter.
On our watchlist
Land Use Code Phase 2 (commercial corridors and centers) continues through 2026 but hasn't touched ADU standards to date.
Check your parcel
The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:
Primary sources
Other Colorado cities
Arvada · Aurora · Boulder · Colorado Springs · Denver · Greeley · Lakewood · Longmont · 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.