Tiny houses on wheels are allowed as caregiver dwellings in Sonoma County, CA, as well as Napa, Lake, Mendocino, Alameda, Contra Costa & Sacramento, according to Sonya Tafejian of
Tiny House Consulting Sonoma County, phone 707-779-9474.

Sonoma County Zoning Code: Section 26-88-010

Residential use of a travel trailer or recreational vehicle shall meet the following standards:
(1) Parcel shall be at least six thousand (6,000) square feet in size.

(2) Use of the travel trailer or recreational vehicle shall be limited to residential use by (a) an ill, convalescent or otherwise disabled friend or relative needing care from the occupant of the primary residence, or (b) a friend or relative providing necessary care for an ill, convalescent or otherwise disabled occupant of the primary residence. The need for care shall be documented by a letter from a physician.

(3) No more than two (2) people may occupy the travel trailer or recreational vehicle.

(4) The temporary unit may only be placed on a legal parcel with an existing primary residence.

(5) The temporary unit shall have an approved connection to the existing or expanded septic system or sanitary sewer system. The unit shall also have an approved connection to the existing well or a public water system.

(6) The temporary unit shall meet zoning setback requirements, scenic resource (SR) requirements and, where applicable, have approval from board or specific plan designated design review committees.

(7) The temporary unit must be currently licensed as required by the Vehicle Code of the state of California, have a valid state insignia and remain in a mobile condition.

(8) The temporary unit shall not be considered a separate residential unit for the purpose of calculating development impact fees (sewer system, park and traffic fees, etc.).

(9) The temporary unit shall not be rented, let or leased.

(10) An administrative permit for residential use of a travel trailer or recreational vehicle shall be obtained. Such permits shall expire one year from the date of issuance. Permits may be renewed annually. Permit and renewal applications shall be accompanied by a written statement, signed by the applicant under penalty of perjury, that the use will conform to the standards set forth in this subsection. Renewal applications shall be submitted prior to permit expiration and shall include an updated letter from a physician.

(11) Within sixty (60) days of cessation of the residential use described in subsection (q)(2) of this section, all occupancy of the unit shall cease and the unit shall be disconnected from all utilities and/or sewage disposal systems.