Accessory Structures in Boulder County, CO (2026)
4 county-level rules, plus city-specific rules for 2 cities in Boulder County, Colorado.
Verified from official government sources
ADU Rules
Unincorporated Boulder County allows accessory dwelling units by right in most residential districts under the Land Use Code (Article 4-516). An ADU must stay in common ownership with the main home, meet setbacks and floor-area limits, and comply with wastewater (OWTS) sizing. Inside Boulder, Longmont, Louisville and Lafayette, city rules
Accessory Dwelling Units in Unincorporated Boulder County
Some RestrictionsBCLUC 4-516 (Accessory Uses)
An accessory use must be a use customarily incidental to and on the same parcel as the main use. A use listed in 4-500 may be an accessory use if the Director determines that the use is customarily incidental to a main use.
Shed & Carport Rules
In unincorporated Boulder County a one-story detached storage shed 120 square feet or smaller (200 sq ft for an agricultural loafing shed) needs no building permit if it is under 12 feet tall, has no utilities, and meets zoning setbacks. Larger sheds require a building permit. Parcel size limits how
Shed and Detached Accessory Building Rules
Some RestrictionsBoulder County B05 (Building Permit Requirements)
One-story detached accessory structures used as storage sheds do not require a building permit if the floor area does not exceed 120 square feet, except agricultural loafing sheds, which may not exceed 200 square feet.
Garage Conversions
Converting a garage into living space, or into an accessory dwelling, requires a building permit and must comply with the Boulder County Land Use Code. A detached garage designed with habitable space (such as a second-floor unit) is treated as an accessory dwelling and counts toward the parcel's Residential Floor
Converting a Garage in Unincorporated Boulder County
Some RestrictionsBCLUC 4-405(C)(3)(b)(iii)
Accessory Dwelling Units (including detached garages designed with Habitable Space on the second floor) must meet the above requirements of 4-405(C)(2) for residential buildings.
Tiny Homes
Boulder County has no separate tiny-home category. A permanent tiny house on a foundation is regulated as a dwelling or accessory dwelling under the Land Use Code and building code; a tiny house on wheels or an RV is not an approved permanent residence outside a licensed manufactured/RV park. Manufactured
Tiny Homes and RVs as Dwellings
Some RestrictionsBCLUC 4-107 (Manufactured Home Park District)
General Requirements. All manufactured homes must be installed using methods and practices which minimize flood damage.
Accessory Structures by City in Boulder County
2 cities in Boulder County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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