5 county-level rules, plus city-specific rules for 2 cities in Jefferson County, Colorado.
Verified from official government sources
Jeffco permits one accessory dwelling unit (ADU) on a single-family detached lot in every agricultural and residential zone. Owner must occupy one unit, max 3 occupants, and a building permit is required. Colorado's HB24-1152 now mandates ADU allowances in metro jurisdictions.
Jefferson County Zoning Resolution Section 19.D.2
Planning & Zoning may permit an accessory dwelling unit (ADU) in all agricultural and residential zone districts, including comparable Planned Development zone districts. The accessory dwelling unit may only be allowed as an accessory use to a single family detached residence.
A detached storage shed 120 sq ft or smaller is a "mini-structure" in Jeffco. Most residential zones cap cumulative mini-structures at 200 sq ft per lot. Sheds must meet the zone-district front setback plus a 5-foot side and rear setback and cannot sit in easements or floodplains.
Jefferson County Zoning Resolution Section 19.B.4.b
Mini-structures must meet the front setback requirement for Accessory Structures as well as a 5-foot minimum side and rear setback.
Jeffco lets you convert an existing qualifying dwelling area into an ADU. Basements may be converted to an ADU regardless of the size or percentage-of-primary-unit cap. Detached ADUs include units above a detached garage. All conversions need a building permit and must meet ADU standards.
Jefferson County Zoning Resolution Section 19.D.2.b(2), Table 1
The maximum square footage is based upon the total square feet in the primary unit, including basements... Basements may be converted to an ADU regardless of the sf or % of primary unit. Detached units include units above a detached garage or other outbuilding.
Carports and garages are accessory structures in Jeffco. Combined accessory square footage (garages, sheds, ADUs, carports) cannot exceed the primary residence's square footage, and an accessory structure's footprint may not exceed 75% of the primary structure's footprint. They must meet the zone-district setbacks and height limits.
Jefferson County Zoning Resolution Section 19.B.7
The footprint of an accessory structure may not exceed 75% of the footprint of the primary structure. The footprint shall include attached garages and fully enclosed porches, but shall not include decks or porches, even if covered.
Jeffco allows shipping containers or conex boxes as the building blocks of a home if they meet zone-district setbacks, building height, and full building-code requirements. A permanent tiny home is treated like any dwelling; a detached one used as a second residence must meet the ADU rules.
Jefferson County Mini-Structures, Sheds, Shipping Containers and Conex Boxes (rev. 07-01-2026)
You could use shipping containers or conex boxes as the building blocks of a home so long as you meet the required property line setbacks and building height requirements of your zone district. However, the structure will need to meet building code requirements.
2 cities in Jefferson County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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