ADU rules in Adams County, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Adams County allows one Accessory Dwelling Unit on any legal single-family lot in any zone district under Section 4-03-03-02-01 of the Adams County Development Standards and Regulations. ADUs must be 500-1,500 sq ft (detached cap), max 25 ft tall, with one off-street parking space. There is no owner-occupancy requirement. Adams County aligned its rules in 2025 with Colorado HB24-1152 (effective June 30, 2025) for surrounding subject jurisdictions.
Adams County originally adopted ADU regulations in 2019 and updated them in 2025 to align with Colorado HB24-1152, the statewide ADU preemption law that took effect June 30, 2025. Although Adams County itself is not a 'subject jurisdiction' under HB24-1152, it adopted the law's framework voluntarily. ADUs are allowed on any legal lot as an accessory use to a single-family home in every zone district. Minimum size is 500 sq ft. Maximum size is 40% of the primary home's floor area or 750 sq ft, whichever is greater, with a hard cap of 1,500 sq ft for detached ADUs. Maximum height is 25 ft, measured to the roof mid-pitch. Detached ADUs must be set back at least 10 feet behind the front structure line of the primary dwelling. Rear setbacks are the greater of 5 feet or the underlying zone district requirement. One off-street parking space is required for the ADU when the underlying zone requires parking, no existing space exists, or on-street parking is prohibited. The ADU cannot be sold separately from the primary dwelling. Permits are obtained through the Adams County E-Permit Center (720.523.6800).
Construction without a building permit is a violation of the Adams County Development Standards. Unpermitted ADUs may be required to come into compliance through an after-the-fact permit, modification, or removal. Selling an ADU as a separate property is prohibited under the development standards.
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See how Adams County's adu rules rules stack up against other locations.
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