State Laws

State Laws


New state laws have made it easier than ever for homeowners to build an ADU.

State laws that went into effect in January 2020 have made it easier than ever to build or convert an existing space into an ADU. Humboldt County has updated their rules about ADUs to match, which include the following:

Building a New ADU

In most cases, homeowners and multifamily property owners are allowed to build an ADU in all residential zones (with limited exceptions). Additionally:

  • parking requirements have been reduced or waived entirely
  • some impact and utility connection fees are waived
  • Homeowners Associations cannot ban ADUs.

Permitting Existing ADUs

State law has created an opportunity for homeowners to bring ADUs built without permits into compliance. However, the county’s Safe Homes Program goes beyond state law by waiving all penalty fees, providing a “no jeopardy” chance to discuss your project with staff without penalty (even if you chose not to permit it) and not enforcing building codes on unpermitted ADUs. The program will be available until 2025. To find out if your property qualifies for this program, contact the Building Division at (707) 445-7245.

Converting Existing Space into an ADU

State law allows homeowners the right to convert many types of existing space into ADUs. The state law covers garages, other accessory buildings (like art studios), or even part of the main house, including attics and basements. To qualify, your property must meet the following criteria:

  • The house must be located in a single-family zone.
  • The structure must have been built legally initially.
  • The ADU must have a door that provides direct access to the outside. (This door can be added during construction if it is not there in the existing structure.)
  • The existing structure must be far enough away from the property line to not be a fire hazard. Discuss specifics with the county.


Jurisdictions cannot charge impact fees—pays for things like roads and parks—for ADUs under 750 square feet and must charge reduced fees for larger ones. (Inspection fees can still be charged.) Water or sewer providers are also not allowed to charge connection fees for existing space converting to an ADU.

For more information, view the Humboldt County Standards.