Tiny Homes: Castro Valley vs Fremont

Can I put a tiny house on wheels in my backyard in unincorporated Alameda County?

California HCD treats tiny houses on wheels as recreational vehicles under ANSI A119.5 standards, not as dwelling units. Alameda County has not published an unincorporated ordinance that authorizes a movable tiny house as a permanent residence the way some California cities have. Confirm with the Alameda County Planning Department at (510) 670-5400 before siting a unit.

What size ADU does Alameda County allow on an unincorporated lot?

Chapter 17.55 of Title 17, adopted by Ordinance O-2024-32, implements California Government Code Section 65852.2. ADUs up to 1,200 square feet are generally available by-right, with a 4-foot side and rear setback minimum for new detached units. Junior ADUs are limited to 500 square feet under Government Code Section 65852.22 and require an owner-occupied R-1 lot.

Does Alameda County allow a tiny house on a permanent foundation?

Yes, when permitted as an Accessory Dwelling Unit under Chapter 17.55. A small foundation-based tiny home of 400 square feet or less can be designed under California Residential Code Appendix Q, which sets specific lofts, ladders, and ceiling-height standards for tiny houses. The unit must still meet ADU setbacks, height, and design standards under Chapter 17.55.

Can I live in a tiny home on wheels in my Fremont driveway?

No. Long-term habitation of RVs and trailers on residential property is prohibited. Short stays by guests (under 7 days) may be allowed. Contact Fremont Code Enforcement for specific rules during family emergencies.

What is the smallest ADU Fremont will permit?

The California Residential Code requires a minimum 150 square feet for a studio dwelling with efficiency kitchen and full bath. Some jurisdictions allow smaller MTH, but Fremont requires CRC compliance which enforces the 150 sq ft floor.