ADU rules in Adams County, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Unincorporated Adams County permits one ADU per single-family home in any zone district. Minimum 500 sq ft; detached units cap at 1,500 sq ft, up to 25 ft tall. A building permit is required and the ADU cannot be sold separately.
Adams County's Development Standards and Regulations (Sec. 4-03-03-02-01) allow one accessory dwelling unit accessory to a single-family home on any legal lot, in any zone district. The minimum ADU size is 500 square feet; an ADU may not exceed 40% of the home's floor area or 750 sq ft (whichever is greater), and a detached ADU tops out at 1,500 sq ft. Detached ADUs can rise to 25 feet measured to roof mid-pitch and must sit at least 10 feet behind the front structure line. There is no owner-occupancy requirement, but a building permit is mandatory (including for modular units) and the ADU stays legally accessory to the main home. Incorporated cities set their own ADU rules.
Building without the required permit triggers stop-work orders and zoning enforcement by Community & Economic Development; unpermitted units must be legalized or removed.
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See how Adams County's adu rules rules stack up against other locations.
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