This is one of the most common questions we hear, and honestly, it’s a foundational misconception for many! Folks often use 'ADU' and 'tiny house' interchangeably, but they're really different beasts. It's not about how many square feet they have, but about their legal status and foundation.
Think of it this way: an Accessory Dwelling Unit, or ADU, is a legal land-use classification. It's a secondary housing unit on your property, tied to your main home, and built on a permanent foundation. This makes it a real estate asset that can build equity.
It’s about zoning and legal definitions. A tiny home, on the other hand, is a descriptive marketing term. It simply describes a small-footprint house, typically under a certain size.
It could be on wheels (a THOW, or Tiny House on Wheels), in which case it's usually considered personal property, like an RV, and tends to depreciate. Or, it could be a tiny house that also happens to be an ADU, if it's on a permanent foundation and meets all the ADU legal requirements.
The critical factor is permanence and legal classification. If your goal is a guest home that adds value to your property and is legally permitted as a secondary dwelling, you're almost certainly looking at an ADU, regardless of its size. If you're imagining a mobile, flexible living space, then a THOW might be your focus. We've been helping people navigate this distinction for over a decade in San Diego. Understanding whether you need an ADU or a true mobile tiny house is the first big step in making your small-space dream a reality.