Humboldt County, CA Accessory Structures: Garage Conversions (2026)

Under Humboldt County Code section 314-69.05.3.8.1 (Inland), one ADU or JADU per lot is principally permitted within the existing footprint of a single-family dwelling or accessory structure such as a garage, including an expansion of up to 150 sq ft beyond the existing dimensions limited to ingress/egress. The ADU or JADU must have separate exterior access from the primary dwelling. Section 69.05.4.5 states '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,' meaning a garage-to-ADU conversion has no setback requirement. Section 69.05.4.1.3 provides that for conversions within the existing space of a single-family residence or accessory structure, 'No new or separate utility connection shall be required between the ADU and the utility, and no related connection fee or capacity charge shall be imposed,' unless the ADU is built concurrently with a new primary dwelling. Section 69.05.4.1.2 prohibits impact fees on any ADU less than 750 sq ft. Approval is ministerial. The conversion is subject to the universal short-term rental prohibition in 69.05.3.4 ('The ADU shall not be rented for periods of 30 days or less') and the ownership rule in 69.05.3.2 (the ADU cannot be sold separately from the principal dwelling). For multifamily structures, section 69.05.3.8.3 allows ADUs within existing non-livable portions such as garages, storage rooms, attics, basements, and passageways, with at least one ADU always permitted and up to 25 percent of the existing multifamily unit count allowed as ADUs.