ADU Rules: Santa Rosa vs Sonoma

Can I build an ADU in Santa Rosa?

Yes. ADUs up to 1,200 square feet are allowed on residential lots. The city offers pre-approved plans and streamlined permitting. Impact fees are waived for units under 750 sq ft.

Do I need extra parking for an ADU?

No additional parking is required if your property is within half a mile of public transit. Otherwise, one space may be required.

Can I build an ADU on my property in unincorporated Sonoma County?

Yes, in almost all cases. Under Sonoma County Code Sec. 26-88-060 and California Government Code 65852.2, ADUs are ministerially permitted in any zoning district that allows a single-family or multi-family primary dwelling, including R1, R2, R3 residential districts; AR and RR rural residential; and the LIA, LEA, DA, and RRD agricultural and resource zones. There is no minimum lot size under state law. You may build a detached ADU up to 1,200 square feet, an attached ADU up to 50% of the primary dwelling (state law guarantees at least 800 sq ft regardless of zoning), or a 500-square-foot JADU within an existing single-family dwelling. The parcel must demonstrate adequate water (well yield testing or public water connection) and adequate septic or sewer capacity. If your parcel is in the Coastal Zone (CC suffix along the Pacific coast or Russian River mouth), Sec. 26C-325.1 applies instead and may retain Coastal Commission review. If your parcel is in a Scenic Resources Combining District under Article 64, objective siting and visual standards apply but discretionary design review is no longer required. Permits are issued through Permit Sonoma; ministerial approval is required within 60 days of a complete application.

Can I rent my Sonoma County ADU or JADU on Airbnb or Vrbo?

No. Both Sonoma County Code Sec. 26-88-060 and Sec. 26-88-061 prohibit renting an ADU or JADU for periods shorter than 30 days, which means short-term and vacation-rental use through Airbnb, Vrbo, and similar platforms is not allowed. This restriction is required by California Government Code 65852.2(a)(6) and 65852.22(a)(7) and applies countywide in unincorporated areas. Long-term tenancies of 31 days or longer are permitted - you can rent the ADU as a year-round rental, month-to-month, or to family members. The County's separate Vacation Rental Ordinance (Sec. 26-88-120) governs short-term rentals of primary dwellings in certain zones with a permit, but does not authorize short-term rental of ADUs or JADUs. Code Enforcement actively monitors short-term rental listings; violations carry administrative penalties under Sec. 1-7 starting at $100 and escalating to $500 per day for continuing violations, plus potential revocation of the ADU permit.

Do Sonoma County ADUs need extra fire-safe construction after the 2017, 2019, and 2020 fires?

Yes, in many areas. Large parts of unincorporated Sonoma County are designated either State Responsibility Area (SRA) by CAL FIRE, Local Responsibility Area Very High Fire Hazard Severity Zone, or Wildland-Urban Interface (WUI) - particularly the Mayacamas, Sonoma Mountain, Mark West Springs, Geyserville, Cazadero, and Annapolis areas burned by the 2017 Tubbs Fire, 2019 Kincade Fire, and 2020 Glass Fire. ADUs in these areas must comply with California Building Code Chapter 7A, which requires ignition-resistant exterior wall coverings, ember-resistant attic and crawl-space vents, multi-pane tempered window glazing, Class A roof assemblies, and non-combustible eaves and decks within 5 feet of the structure. Public Resources Code Section 4291 and Sonoma County Code Chapter 13A also require defensible space: a 0-30 foot 'lean, clean, and green' zone immediately around the structure and a 30-100 foot 'reduced fuels' zone, both maintained year-round. Permit Sonoma Fire Prevention conducts inspections, and CAL FIRE may issue separate citations. Confirm your parcel's hazard designation through the Permit Sonoma Wildfire Resilience Map or the CAL FIRE Fire Hazard Severity Zone viewer before designing your ADU.

Can I sell my Sonoma County ADU separately from the main house?

Not currently. California AB 1033 (2023, Government Code 65852.26) authorizes local agencies to adopt an ordinance allowing ADUs to be sold as separate condominium units under the Davis-Stirling Common Interest Development Act, but the local jurisdiction must opt in by adopting its own ordinance. Sonoma County has not adopted an AB 1033 ordinance, so ADUs in unincorporated Sonoma County cannot be sold or conveyed separately from the primary dwelling. As of early 2026, only a small number of California jurisdictions - including the cities of San Jose, Berkeley, and Santa Monica, and unincorporated San Diego County - have adopted AB 1033 ordinances. If you want to sell an ADU separately, you would need to either wait for the Board of Supervisors to adopt a local AB 1033 ordinance, or pursue a traditional lot split / subdivision under the Subdivision Map Act, which requires meeting minimum lot size, frontage, and infrastructure requirements that most ADU parcels cannot satisfy. The properties remain legally one parcel and the ADU is part of the same fee-simple ownership as the primary dwelling.