ADUs are allowed in Fort CollinsTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Fort Collins, CO
Is your property eligible for an ADU?
# of Properties
56,911
Owner-occupied
69%
Zoning districts
61
Median Lot Size
0.16 acres
Avg Income
$100,902
Residential Types:
56,911 housing units
Apts (4+ units)
3%
Other
97%
Zoning Districts:
73,995 parcels · 61 districts
RL
34%(25,142)
LMN
26%(18,981)
MMN
8%(5,878)
MH
7%(4,925)
Other
26%(19,069)
ADU Rules
What can you build in Fort Collins, CO?
Fort Collins, CO follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum size when located at or above grade: the greater of 750 sq ft or 45% of the primary dwelling’s gross floor area, but not exceeding the primary dwelling’s area.
- –Maximum size when located below grade (basement): the greater of 750 sq ft or 100% of that floor level (modeled as basement area).
Detached ADU Size Limits
- –New detached ADU size: 750 sq ft if the primary dwelling is 1,667 sq ft or smaller; otherwise the lesser of 1,000 sq ft or 45% of the primary dwelling’s floor area.
Max Units
- –Detached house & Mobile Home lots: 1 ADU per lot
- –Duplex/Triplex: UE - 0 ADU; OT-B - 1 ADU per lot; total units not to exceed four (4) on a lot
- –Residential Cluster: lots with a detached house may include 1 ADU in addition to the max dwelling units
Parking
- –No ADU-specific min/max; one tandem space may count toward the required minimum
Rental Restrictions
- –Short-term rentals (<30 days) prohibited in ADUs; license required to operate any short-term rental; existing licenses may be renewed.
ADU State Law
What can you build in Colorado?
- –ADUs must be approved based on objective standards; no discretionary hearings allowed.
- –Historic properties: Local historic review may still apply in designated historic districts.
- –Exempt parcels: ADUs are not required to be allowed on parcels without adequate water/sewer, in floodways, or on certain historic properties.
- –HOAs cannot prohibit ADUs: HOA rules that conflict with the state ADU law are void.
- –Parking exceptions exist: In rare cases, one parking space may be required if there is no existing off-street parking and on-street parking is prohibited.
- –Local rules still matter: Building code, fire code, utility capacity, and life-safety standards still apply.
- –More permissive is allowed: Municipalities may allow larger ADUs, multiple ADUs, or additional housing types beyond what the state requires.
- –Local zoning controls whether ADUs are allowed at all.
- –HOA rules may still apply.
- –More permissive local rules are allowed.
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other Colorado municipalities
Rules change at the town line. Check the municipality your property is actually in.
Larimer County