Tiny Home on Wheels vs. Foundation: Which Can Be an ADU in California?
Choosing wheels or a foundation decides almost everything else: where you can put the home, which permits you need, and how you can finance it.
Side by side
On wheels (THOW / park trailer) | On a foundation | |
Built to | ANSI A119.5 or NFPA 1192 (IB 2016-01) | California Residential/Building Code (IB 2016-01) |
Size limit (state) | 400 sq ft gross for park trailers, lofts may be excluded (HSC §18009.3) | Set by zoning/ADU rules; an ADU of at least 800 sq ft must be allowed (HCD ADU Handbook) |
Registered with | DMV (required by the local THOW ordinances in San Diego, Los Angeles, Santa Cruz County) | County assessor (real property) |
Counts as ADU under state law? | Generally no (HCD, 2025) | Yes, if it meets the ADU definition |
Where allowed | Parks, plus places with a local THOW ordinance | Anywhere zoning allows a house or ADU |
Moving it | Needs a transport permit (Vehicle Code §35780, per IB 2016-01) | Not meant to move |
Choose wheels if…
Your city or county has a THOW ordinance, or you plan to live in a park.
You may move the home later.
You want a certified home built off-site and delivered.
Choose a foundation if…
You want the strongest legal footing in a backyard (state ADU law).
You want the home to add to the property's value as real estate.
Your area has no THOW ordinance.
Things people miss
Local THOW rules usually require hookups. The San Diego (city) and Santa Cruz County rules require water, sewer and electric connections. Santa Cruz does not accept a composting toilet in place of sewer/septic. (SDMC §141.0318, Santa Cruz County)
Wheels usually stay on. The City of San Diego and Santa Cruz County require the wheels to remain, with the undercarriage skirted or concealed.
Fire zones add rules (sprinklers, noncombustible walls) in some places. See the county guides.
Not sure which fits your lot? That is exactly what a site assessment answers.
Frequently asked questions
Can a tiny house on wheels be an ADU in California?
Generally not under state law: HCD says movable tiny homes may not meet the ADU definition (HCD, 2025). Some local rules allow them anyway, such as the City of Los Angeles, the City of Fresno, Placer County and Nevada County, while Santa Cruz County says they may not be permitted as ADUs.
Tiny home vs ADU: which costs less?
It depends on size, site work and finishes, and a tiny home on a foundation can itself be an ADU. ADUs of 750 sq ft or less pay no impact fees (HCD ADU Handbook). See our cost guide.
Do you need a permit for a tiny house on wheels?
Yes, to live in one outside a park. Local ordinances require a permit, certification and DMV registration, and parks have their own rules.
Can I move a foundation tiny home later?
Not easily. A foundation home is built as real property and isn't meant to move, so choose a certified home on wheels if you may move.
Related guides
Floor Plan Preview
Here's a look at two of the designs Zen Tiny Homes can build. Every plan can be adjusted to fit your lot.
Grove House: 3D render
Grove House: floor plan
See all the layouts in California Tiny Home Floor Plans.
Ready to plan your tiny home?
Zen Tiny Homes in San Diego designs and builds tiny homes (Alpine, Mammoth, Container, and fully custom). Fill out the free Buyers Application and we'll help you choose the right path for your site and budget.
Prefer to talk? Call Zen Tiny Homes at 760-492-0742 or visit zentinyhomes.com.
This guide is general information, not legal advice. Rules change. Zen's $500 site assessment checks what fits your lot, or call 760-492-0742.
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