Placer, Humboldt, Nevada, San Diego, Santa Cruz, Sonoma, and Fresno counties are the California counties that allow tiny houses under published ordinances or permitting guidelines that name them by type. Beyond those seven, state ADU law makes a foundation-based tiny house at least theoretically permissible in every county, because no county can prohibit an accessory dwelling unit on a lot with an existing single-family home. What varies from county to county is whether tiny houses on wheels are welcomed, tolerated on a temporary basis, or effectively kept out.
Foundation or Wheels Decides Almost Everything
Before comparing counties, know which kind of tiny house you have. California treats the two very differently.
A tiny house on a permanent foundation is a building. On a lot with an existing home it falls under California’s accessory dwelling unit statutes; on its own lot it must meet the full California Building Standards Code. Either way it needs building permits, utility connections, and zoning compliance. California has also adopted Appendix AQ of the Residential Code, which defines a tiny house as a dwelling of 400 square feet or less (excluding lofts) and sets construction standards including a 6-foot-8-inch minimum ceiling in living spaces and a 6-foot-4-inch minimum in bathrooms and kitchens. Any loft must be at least 35 square feet with no dimension shorter than 5 feet.1International Code Council. 2022 California Residential Code – Appendix AQ Tiny Houses Appendix AQ is not automatic; each county or city must adopt it locally.
A tiny house on wheels is a recreational vehicle under California Health and Safety Code Section 18010. It must contain less than 320 square feet of internal living area, have no more than 400 square feet of gross area, sit on a single chassis, and be towable on public highways without a special permit.2California Legislative Information. California Health and Safety Code Section 18010 Living in one full-time triggers a different set of local rules than pouring a slab and framing a small house, and this is where county-by-county policy actually diverges.
The Statewide Floor Every County Has to Meet
California ADU law, recodified into Government Code Sections 66310 through 66342, sets a floor no county can go below. Every county must allow at least one detached ADU of up to 800 square feet on any lot with an existing or proposed single-family home. Side and rear setbacks cannot exceed four feet. Counties can set maximum ADU sizes by ordinance, but they cannot cap detached ADUs below 850 square feet for a studio or one-bedroom, or below 1,000 square feet for two bedrooms or more. Counties that lack a compliant ADU ordinance must allow detached ADUs up to 1,200 square feet by default.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
The state also created junior ADUs of 500 square feet or less built entirely within an existing single-family home. A JADU requires owner-occupancy in either the main home or the JADU, a separate entrance, and an efficiency kitchen.4California Legislative Information. AB-68 Land Use – Accessory Dwelling Units Converting a room or garage into a JADU is often the simplest legal path to a very small dwelling.
Two other statewide rules matter. Counties have 60 days to approve or deny a complete ADU application; if they miss the deadline, the application is deemed approved. And ADUs of 750 square feet or less are exempt from impact fees.3California Department of Housing and Community Development. Accessory Dwelling Unit Handbook Detached ADUs get a base 16-foot height limit, rising to 18 feet near major transit stops, with two extra feet allowed to match a primary home’s roof pitch.
The result: a foundation-based tiny house built as an ADU is possible in every California county. The seven counties below have gone further and spelled out how they handle tiny houses (and, in most cases, tiny houses on wheels) specifically.
Placer County
Placer County is one of the most tiny-house-friendly jurisdictions in the state. In 2022, the county approved amendments allowing moveable tiny homes in three roles: as ADUs, as primary residences in certain zones, and in dedicated cluster-lot communities.5Placer County. Tiny Homes in Placer County
Placer defines a moveable tiny house as an independent living space of no more than 400 square feet on a wheeled trailer chassis, with a bathroom, kitchen, and sleeping area. It has to look like a conventional home built from standard materials, not a traditional RV or mobile home, and it must be licensed and registered with either the DMV or the state Department of Housing and Community Development. Once sited, the undercarriage, wheels, axles, tongue, and hitch must be concealed; wheels can be skirted or removed, and the unit sits on leveling or support jacks over a paved surface. Placer requires four feet of fire separation from adjacent lot lines and ten feet from other structures on the same lot.5Placer County. Tiny Homes in Placer County
Humboldt County
Humboldt County’s zoning code names both tiny houses and moveable tiny houses as distinct categories and allows them as ADUs when developed consistent with the county’s ADU ordinance.6Humboldt County. Humboldt County Code 314-69 – Accessory Dwelling Units Humboldt is also one of the few counties that spells out the wheel-removal process. If you take the wheels off a moveable tiny house and set it on a foundation, the foundation must meet state-approved manufactured housing standards or carry a licensed engineer’s certification. That conversion also shifts the unit from a DMV-registered vehicle to real property assessed alongside the land.
Nevada County
Nevada County publishes a permitting checklist built specifically for tiny homes on wheels. An applicant has to submit a site plan, floor plan, third-party certification such as ANSI A119.5, skirting details, anchorage plans with engineering, stair and landing plans, and DMV registration. The unit has to meet the setbacks for its zoning district and connect to county-approved water and sewer.7Nevada County. Tiny Home on Wheels Checklist
San Diego County
San Diego County added tiny homes on wheels to its housing options in unincorporated areas, allowing them both as standalone dwellings and as ADUs. The rules are among the most detailed in the state:8County of San Diego. County Adds Tiny Homes on Wheels to Housing Options
- No larger than 430 square feet measured inside the walls, no taller than one story, no slide-outs or pop-outs.
- Connections to electric, water, and sewer, with building permits for each.
- Non-combustible exterior (stucco, masonry, cement fiber board, or metal), dual-glazed windows, a Class A roof, and residential fire sprinklers unless the ADU sprinkler exemption applies.
- Cannot move under its own power, and must sit on a paved pad with bumper guards or curbs.
THOW density on a given lot is tied to the number of homes the zoning ordinance allows there.
Santa Cruz County
Santa Cruz County allows tiny homes on wheels, but with a significant limit: following guidance from the state Department of Housing and Community Development, the county no longer permits THOWs as ADUs. They are processed like other residential projects and must go through plan review.9Santa Cruz County. Tiny Homes on Wheels Permit
The manufacturer’s ANSI A119.5 certification has to be in hand before you can even submit the building permit application. The unit has to be braced and secured with seismic tiedowns, and the wheels stay attached. The parking pad has to be level, with at least two inches of asphalt concrete over five inches of base rock. Permit fees run around $2,000.9Santa Cruz County. Tiny Homes on Wheels Permit
Sonoma County
Sonoma County draws a hard line. Tiny homes on permanent foundations can serve as primary residences, ADUs, or cottage housing developments as long as they meet all building, fire, and zoning codes. RVs do not qualify for any of those permanent categories.10Permit Sonoma. Tiny Houses
Tiny houses on wheels (the county calls them “transportable housing units”) are allowed only temporarily, in limited situations: during construction of a primary dwelling, before an ADU is built, to house a family member with a medical need, to shelter wildfire victims, or as temporary farmworker housing. Those permits generally last up to one year, and the unit must meet California Building Code or ANSI standards with no more than 400 square feet of interior living space.10Permit Sonoma. Tiny Houses
Fresno County
Fresno County recognizes two legal paths. A tiny home on a chassis with wheels must be 400 square feet or less, is treated as an RV, and falls under local enforcement rather than state HCD jurisdiction. A tiny home without wheels has to sit on a foundation, comply with the California Building Standards Code, and go through local permitting.11County of Fresno. Building and Safety FAQs Whether a specific parcel’s zoning district actually allows a tiny home varies, so the county recommends calling zoning enforcement before you buy or place a unit.
Cities Worth Knowing If You’re Inside City Limits
County rules govern unincorporated land. If your property sits inside an incorporated city, the city’s ordinance applies instead, and two are worth flagging.
San Luis Obispo permits one tiny home on wheels per owner-occupied property through a Director’s Action Permit. The THOW cannot exceed 400 square feet excluding a loft, and it must carry both DMV registration and ANSI certification. San Luis Obispo requires the wheels to stay on; removing them reclassifies the unit as a standard dwelling or ADU subject to the full building code. Permits run three to five years and can be renewed on inspection.12City of San Luis Obispo. Tiny Home on Wheels
The City of Los Angeles approved an ADU ordinance that specifically permits movable tiny houses as permanently habitable accessory dwelling units. Unincorporated Los Angeles County also allows tiny homes as ADUs under the statewide framework, though the county has not published a THOW-specific ordinance as detailed as the seven above.
If Your County Isn’t on the List
The seven counties profiled here are the ones with clearly published tiny house policies. They are not the only places a tiny house can be legal. Because state law requires every county to allow ADUs, a tiny house on a permanent foundation is at least possible everywhere in California. The real question is always whether your specific parcel’s zoning district, lot size, and existing development actually support one.
Call your county’s planning or building department directly. Ask three things: whether the county has adopted Appendix AQ of the California Residential Code, whether it has any THOW-specific ordinance, and what the ADU size minimums and setback requirements are for your zone. Many planning departments publish ADU guides and permit checklists online. If staff cannot answer clearly, request a pre-application meeting. Most counties offer them at no cost, and a short meeting up front is cheaper than a set of plans that turn out not to meet local standards.