ADU rules in Humboldt County, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Humboldt County permits accessory dwelling units (ADUs) and junior ADUs in any zone allowing single-family or multifamily residential use, with ministerial 60-day approval, 4-foot side/rear setbacks, detached size cap of 1,200 sq ft, attached cap of 50% of the primary residence, and a prohibition on short-term rentals of 30 days or less.
Inland Zoning Regulations section 314-69.05 (added by the September 1, 2020 Board of Supervisors ordinance) sets the standards for accessory dwelling units in unincorporated Humboldt County outside the Coastal Zone, and is the local implementation of California Government Code section 65852.2. Under subsection 69.05.2 the county must act on a complete ADU building permit application within 60 days when an existing single-family or multifamily dwelling is on the lot. One or more ADUs are permitted per lot with a single-family or multifamily dwelling (69.05.3.1); on AE-zoned parcels of 40 acres or larger, an ADU unrestricted in size may be allowed. Detached ADUs are capped at 1,200 sq ft of floor area, attached ADUs at 50 percent of the existing primary residence, and the minimum floor area is 150 sq ft (69.05.4.3); floor area excludes sheds, garages, and storage areas. Setbacks under 69.05.4.5 are zero for conversions of existing living area or accessory structures or rebuilds in the same footprint, and no more than 4 feet from side and rear lot lines for new construction. One parking space is required per ADU and may be tandem on a driveway, with broad exemptions (transit, historic district, structure conversion, mapped Housing Opportunity Zones for ADUs under 1,000 sq ft). The ADU may not be sold separately from the primary dwelling (69.05.3.2) and may not be rented for periods of 30 days or less (69.05.3.4). Fire sprinklers are not required for the ADU if not required for the primary residence. A Junior Accessory Dwelling Unit (JADU) is treated as an attached unit within the footprint of a primary dwelling, conforming to Gov. Code section 65852.22, and is principally permitted wherever ADUs are. In ADU Special Permit Areas (areas outside fire protection districts, in airport zones, on landslide/liquefaction sites, with inadequate water/sewer, flood/tsunami hazards, or near toxic cleanup sites), a Special Permit may be required.
Building an ADU without a permit, exceeding floor-area caps, violating setbacks, or renting an ADU for periods of 30 days or less are zoning violations enforceable by the Planning & Building Department; certificate of occupancy may be withheld until violations are corrected. An ADU built before the ordinance effective date that receives a building code violation notice may request a delay in enforcement of up to five years under 69.05.7 if the correction is not required to protect health and safety.
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