ADU rules in Jefferson County, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
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.
Under Section 19.D of the Jefferson County Zoning Resolution, Planning & Zoning may permit one ADU (attached or detached) accessory to a single-family detached residence in all agricultural and residential zone districts. Detached ADUs need at least 7,500 sf of lot; on lots of 1 acre or more the ADU may be 1,200 sf or 40% of the primary unit, whichever is less (smaller caps on smaller lots). The owner must occupy the primary or accessory unit as their primary residence. Colorado HB24-1152 (effective June 30, 2025) separately requires many metro-area jurisdictions to allow one ADU wherever single-unit detached dwellings are permitted, removing owner-occupancy and extra-parking barriers.
Building an unpermitted second dwelling is a zoning violation enforced under C.R.S. 30-28-124; the County can require removal and pursue civil penalties. A recorded notice ties the ADU permit to the property.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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See how Jefferson County's adu rules rules stack up against other locations.
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