ADU rules in Douglas County, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Unincorporated Douglas County allows one accessory dwelling unit (ADU) per lot in the A-1 Agricultural district. A detached ADU needs at least one acre on central water, or two acres on a well. A second ADU is allowed only on parcels of 35 acres or more.
The Douglas County Zoning Resolution (Section 303.01) lists an ADU as a permitted accessory use in the A-1 district, one per lot, once a principal dwelling exists. Section 306.01 requires a one-acre minimum lot for a detached ADU on central water; 306.02 requires two acres if served by an individual well. A second ADU is possible only on 35+ acres, subject to Section 325 standards and Board approval. Incorporated towns (Castle Rock, Parker, Lone Tree) set their own ADU rules. Colorado's 2024 ADU law (HB24-1152) also requires many metro-area jurisdictions to permit one ADU where single-family homes are allowed.
Building and using an ADU without required zoning approval and a building permit is a zoning violation subject to county enforcement, stop-work orders, and abatement.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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