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Larimer County, CO Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified July 2026

ADU rules in Larimer County, CO, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Units per lot: One ALA per lot
Max size (small lot): 900 sq ft
Max size (large lot): 1,200 sq ft
Permit: Building permit required
Planning review: Waived since June 30, 2025

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Colorado under recent ADU streamlining laws. The Larimer County, CO rules below cover local size, height, and setback requirements.

Summary

Unincorporated Larimer County allows one Accessory Living Area per lot as a use by right. Since June 30, 2025 (HB24-1152) no planning review is needed before applying for the building permit. Size is capped by lot size under Table 3-15.

City-specific rules exist: Loveland, and Fort Collins have their own adu rules rules that differ from Larimer County's county-level regulations. If you live in one of those cities, check the city-specific page instead.

With the passage of Colorado House Bill 24-1152, which goes into effect June 30, 2025, Larimer County no longer requires applicants to go through a planning process before applying for an Accessory Living Area building permit. One accessory living area is permitted per lot.

Source: Larimer County - Accessory Living AreasView official code

Full Breakdown

Larimer County Land Use Code §3.4.5.A permits one accessory living area (the county's ADU) per lot wherever single-unit detached dwellings are allowed. Maximum floor area scales with lot size: 900 sq ft on lots up to 15,000 sq ft, 1,000 sq ft up to 100,000 sq ft, and 1,200 sq ft on larger lots (75% of the main dwelling, whichever is less), and an ALA may never exceed the size of the principal dwelling. A building permit and applicable impact fees are required, and signed utility approval forms must be submitted first. Incorporated cities (Fort Collins, Loveland, Estes Park) set their own ADU rules.

Violations & Fines

Building an unpermitted ALA is a Land Use Code violation subject to code compliance action, stop-work orders, and after-the-fact permitting.

Frequently Asked Questions

Do I still need a special review for an ADU?

No. After Colorado HB24-1152 (effective June 30, 2025), Larimer County no longer requires a planning process before you apply for an Accessory Living Area building permit.

How big can my ADU be?

It depends on lot size under Table 3-15, up to 900 to 1,200 sq ft, and it can never exceed 75% or the size of the main dwelling.

Sources & Official References

Other rules in Larimer County

Parking Rules: Overnight ParkingSome Restrictions Parking Rules: Street Parking LimitsSome Restrictions Shed & Carport RulesSome Restrictions Tiny HomesSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: EV ChargingSome Restrictions Parking Rules: Commercial & Oversized VehiclesSome Restrictions Parking Rules: Driveway RulesSome Restrictions

All Larimer County rules

How Larimer County compares: Easiest Cities to Build an ADU·Compare Larimer County to another location·View the Colorado accessory structures overview

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ADU Rules in Cities Across Larimer County

Fort Collins, CO Loveland, CO