5 county-level rules, plus city-specific rules for 2 cities in Boulder County, Colorado.
Verified from official government sources
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
BCLUC 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.
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
Boulder 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.
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
BCLUC 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.
Carports are accessory structures under the Boulder County Land Use Code and must meet the zoning district's setbacks and height limits. Because a carport lacks two rigid walls, the code treats it differently from enclosed buildings in floodplains, where it may be built at grade with flood-resistant materials. Most carports
BCLUC 4-405(C)(3)(b)(ii)
Accessory structures that do not have at least two rigid walls, including but not limited to carports, gazebos, and picnic pavilions, may be constructed at grade and must use flood-resistant materials up to the FPE.
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
BCLUC 4-107 (Manufactured Home Park District)
General Requirements. All manufactured homes must be installed using methods and practices which minimize flood damage.
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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