ADUs and Tiny Homes Are Not the Same — Here's Why

People use "tiny home" and "ADU" like they mean the same thing. They don't — and the difference has real consequences.

"Tiny home" describes a size. "ADU" describes a legal status.

A tiny home is just a small dwelling, usually under 400 square feet. That tells you nothing about whether it's legal to live in.

An ADU is a legal category: a permitted dwelling unit that meets building code, sits on a permanent foundation, and is approved by your city. When your ADU is finished, it gets a certificate of occupancy. It's real housing — you can rent it out long-term, insure it, and count it in your property's value.

Tiny home on a foundation vs. tiny home on wheels

A small home built on a permanent foundation with permits is an ADU — it's just a small one. Perfectly legal.

A tiny home on wheels is a different animal. Legally, it's usually treated like an RV or a park trailer, not a dwelling. Some California cities have started allowing movable tiny homes as ADUs under specific rules, but many haven't. If you park one in your backyard and rent it out without approval, you may be running an illegal rental that can't be insured and can trigger code enforcement.

Why it matters for your wallet

Permitted ADUs can be financed, appraised, and rented legally. Unpermitted tiny homes generally can't. A $60,000 tiny home on wheels that the city won't recognize may add zero appraised value; a $250,000 permitted ADU commonly adds more than it cost in strong rental markets.