Humboldt County, CA Accessory Structures: ADU Rules (2026)
ADU rules in Humboldt County, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Code Section
- Humboldt County Code section 314-69.05 (Inland) / 313-69.05 (Coastal)
- Maximum detached ADU size
- 1,200 sq ft (minimum 150 sq ft)
- Maximum attached ADU size
- 50% of the primary residence floor area
- Minimum side/rear setback
- 4 feet (zero for conversions or rebuilds in existing footprint)
- Parking
- 1 space per ADU, tandem allowed; multiple statutory exemptions
- Short-term rental rule
- Cannot be rented for terms of 30 days or less (69.05.3.4)
- Permit timeline
- 60-day ministerial action required once application is complete
Summary
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.
69.05.2 Accessory Dwelling Units Generally Permitted. Accessory dwelling units may be principally permitted in any zone that allows single family or multifamily dwelling residential use and includes a proposed or existing dwelling, if the General Provisions in 69.05.3 are met, and the ADU meets the Development Regulations and Standards of section 69.05.4. ... The county shall act on a complete building permit application for an accessory dwelling unit within 60 days from the date the completed application is received if there is an existing single-family or multifamily dwelling on the lot. ... 69.05.3.4 Short-term Lodging Prohibited. The ADU shall not be rented for periods of 30 days or less. ... 69.05.4.3 Total Floor Area. The total floor area of a detached ADU shall not exceed 1200 square feet. If there is an existing primary residence, the total floor area of an attached accessory dwelling unit shall not exceed fifty (50) percent of the area of the existing primary residence. The minimum floor area shall be 150 square feet. Floor area includes all enclosed habitable living space but excludes sheds, garages and storage areas. ... 69.05.4.5 Setbacks. No setback shall be required for an ADU or a portion of an ADU, converted from an existing living area or accessory structure, or a structure constructed in the same location and to the same dimensions as an existing structure. A setback of no more than four feet from the side and rear lot lines shall be required for an ADU that is not converted from an existing structure or a new structure constructed in the same location and to the same dimensions as an existing structure. 69.05.4.6 Parking. Each ADU requires one (1) parking space. These spaces may be provided in tandem on a driveway. Off street parking shall be permitted in setback areas or through tandem parking, unless specific findings are made that parking in setback areas or tandem parking is not feasible based upon specific site or regional topographical or fire and life safety conditions.
Full Breakdown
2. 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. 1); on AE-zoned parcels of 40 acres or larger, an ADU unrestricted in size may be allowed. 3); floor area excludes sheds, garages, and storage areas. 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). 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. 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.
Violations & Fines
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.
Frequently Asked Questions
Can I build an ADU on my unincorporated Humboldt County property?
Can I short-term rent (Airbnb) my Humboldt County ADU?
How long does Humboldt County have to approve my ADU permit?
Do I need extra parking for an ADU?
Sources & Official References
Other rules in Humboldt County
How Humboldt County compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Humboldt County to another location·View the California accessory structures overview
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