ADU rules in Boulder, CO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Boulder allows ADUs on most residential lots. The city adopted progressive ADU regulations permitting both attached and detached units with streamlined permitting for smaller units under 500 square feet.
Boulder updated its ADU ordinance to comply with HB 24-1152 and expanded allowances beyond the state minimum. Both attached and detached ADUs are permitted on single-family and duplex lots. Maximum ADU size is 1,000 square feet or 50% of the primary dwelling. Units under 500 square feet qualify for streamlined permitting. No additional parking required for ADUs near transit stops along the Flatiron Flyer corridor. Owner occupancy is not required. ADUs may not be used as STRs without a separate STR license. Design standards apply in historic districts.
Unpermitted ADU: standard building code enforcement. May require demolition or legalization. Occupying unpermitted dwelling: code violation.
Boulder, CO
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See how Boulder's adu rules rules stack up against other locations.
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