ADU rules in Arapahoe County, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Arapahoe County approved ADUs in unincorporated areas effective September 12, 2023, under LDC Section 3-3.2 D. Three types are permitted: internal, attached, and detached. Minimum lot size is 5,000 sq ft. Owner occupancy is required and short-term rental is prohibited.
Arapahoe County allows accessory dwelling units in all agricultural and most residential zones on lots of at least 5,000 square feet, per LDC Section 3-3.2 D effective September 2023. Type 1 (internal) and Type 2 (attached) ADUs can be up to 50% of the existing home's square footage. Type 3 (detached) ADUs range from 600 to 1,200 square feet depending on lot size, with no maximum on lots of 19 or more acres. Urban-area ADUs are limited to two bedrooms on lots under 19 acres. The property owner must reside in either the principal dwelling or the ADU. Short-term rental (under 30 days) of ADUs is prohibited. Building permits are required with a typical 8 to 12 week review period. HOAs may prohibit ADUs through private covenants despite the county approval.
Construction without permits faces stop-work orders. Operating an ADU as a short-term rental violates the LDC. Non-owner-occupied ADUs are prohibited.
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See how Arapahoe County's adu rules rules stack up against other locations.
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