About Humboldt ADU
Humboldt ADU is a program developed by Humboldt County to support and inform homeowners who are interested in building Accessory Dwelling Units (ADUs). The program was established as part of a goal outlined in the County's 2019 Housing Element, with the aim of encouraging ADU development as a means to increase the supply of affordable housing in the region.
Humboldt County, like much of California, has faced a persistent housing shortage. Opportunities to build new homes can be difficult to come by, particularly housing that remains affordable. For many workers and families, purchasing a home is out of reach, while renters are facing prices that are increasingly difficult to manage. Developing ADUs — also known as granny flats, backyard cottages, or in-law units — is one practical way to help address this challenge at the local level.
What Is an ADU?
An Accessory Dwelling Unit (ADU) is a secondary housing unit on a residential property. These units go by many names, including granny flats, backyard cottages, in-law suites, and converted garages. They can serve a wide range of purposes — from housing family members to generating rental income — and can adapt as a homeowner's needs change over time.
Humboldt ADU provides information on several types of ADUs that homeowners in the county may consider building:
- Detached ADU — A freestanding structure, such as a backyard cottage, separate from the primary home
- Attached ADU — A unit that shares at least one wall with the primary house
- Garage Conversion — A former garage space converted into a living unit
- Interior Conversion — Existing interior space, such as an attic or basement, converted into a dwelling
- Above or Below Garage — New or converted space located above or below an existing garage
- Junior ADU (JADU) — Up to 500 square feet of converted interior space within a single-family home
In Humboldt County, detached ADUs can be up to 1,200 square feet without a Special Permit, up to 16 feet tall (or 25 feet on larger residentially zoned lots), and must maintain at least 4-foot side and rear yard setbacks. Attached ADUs can also reach up to 1,200 square feet, or up to 50% of the size of the existing primary home. Junior ADUs (JADUs) are limited to 500 square feet, must be located within the existing walls of the primary home or attached garage, and require the owner to occupy the primary residence.
Benefits of Building an ADU
Building an ADU can offer homeowners a range of practical benefits, while also contributing to the broader community:
- Family flexibility — ADUs can provide a close but separate living space for parents, grandparents, adult children, or family members with disabilities, allowing families to stay connected while maintaining privacy.
- Financial security — Renting an ADU can generate a steady source of income, help cover mortgage costs, and potentially increase property value over time.
- Adaptability — As life circumstances change, an ADU can shift in purpose — from housing a family member to serving as a rental unit or a space to downsize into.
- Community impact — ADUs often provide housing for local workers and families who play essential roles in the county but struggle to find affordable options.
Humboldt ADU offers resources to help homeowners navigate the entire process, from clarifying goals and understanding what can be built on a given property, to working through the permitting process and managing construction. While it is possible to act as an owner-builder, the program recommends working with a licensed ADU contractor or a design/build team to ensure the project is completed properly and efficiently.
The program also provides access to an interactive guidebook covering ADU basics, budgeting, financing, design considerations, and guidance on working with the county. Floor plans and additional resources are available to help homeowners make informed decisions before beginning their project.