What Is an ADU? How It's Different From an RV Travel Trailer or Park Model Tiny Home

"ADU" is showing up everywhere in housing conversations lately, but it's a newer term and a lot of people searching for a small second home on their property haven't heard it yet, or assume it means the same thing as an RV travel trailer or a park model tiny home sitting at an RV resort. It doesn't. The three are legally and practically different, and mixing them up can mean ordering the wrong thing for what you're actually trying to do.

What is an ADU, exactly?

ADU stands for accessory dwelling unit: a secondary, permitted home built on the same lot as an existing primary residence. The key word is "permitted." An ADU is designed, built, and inspected under the same residential building code as the main house on the property, not under a separate vehicle code. It's meant to be lived in long-term, it typically needs permanent utility connections, and once it's approved, it's treated by your city as real property, not as something parked on the lot.

ADUs can be attached to the main house, a conversion of existing space like a garage, or fully detached, a standalone small structure elsewhere on the same lot. Detached is the category most people mean when they picture a backyard cottage or a small guest home, and it's the category laws like Utah's SB284 are written around.

How an ADU differs from an RV travel trailer

A travel trailer is built and certified to recreational-vehicle industry standards, not the residential building code your house falls under. It's designed to be towed, used seasonally or for travel, and in most states it's titled and registered like a vehicle rather than treated as real property. That distinction carries through to zoning: most city codes separately restrict or prohibit living full-time in an RV on an ordinary residential lot outside of a licensed RV park or campground, regardless of how long you intend to stay. Parking a travel trailer in your backyard doesn't make it a legal ADU, even if it functions like one day to day.

How an ADU differs from a park model tiny home

Park model tiny homes look closer to a small house than a travel trailer does, and they're genuinely popular in RV resorts and seasonal communities, but they're still built and classified under recreational-vehicle industry standards, not residential building code, and they're typically capped around 400 square feet. Like a travel trailer, a park model is generally titled as an RV, not as real property, and most residential zoning codes don't recognize one as a legal accessory dwelling unit just because it's parked on a lot long-term.

Why the distinction actually matters

• Zoning and legality. Laws that open the door to backyard housing, like Utah's SB284, apply specifically to permitted, code-built accessory dwelling units. They don't apply to parking a recreational vehicle on a residential lot, even one that looks like a tiny house.
• Permits and inspections. An ADU goes through your city's standard building permit and inspection process. An RV or park model generally doesn't, because it isn't being built as a permanent structure on your property.
• Property value and financing. A completed ADU adds to your home's appraised real property value and can sometimes be rolled into a mortgage, HELOC, or construction loan. RVs and park models are financed and insured like vehicles, a depreciating asset, separate from your home's value.
• Utilities. An ADU needs permanent, code-inspected water, sewer or septic, and electrical connections. RVs and park models often run on RV-park hookups or onboard tanks instead.

So where does a unit like ours fit?

A factory-built, steel-framed unit like the X1 Foldable or the X3 Expandable isn't sold or titled as a recreational vehicle off an RV lot. But whether a specific unit on your property is treated as a legal ADU, the same way a stick-built backyard cottage would be, always comes down to how it's installed (on a permanent foundation or piers versus wheels), what utility connections it has, and what your local zoning code says, not the product name alone. We can't make that call for you sight unseen; your city or county building department can.

Before you decide what to buy

1. Read our SB284 explainer if you're in Utah, or call your own city or county planning department anywhere else, and ask specifically what's required for a legal accessory dwelling unit on your lot.
2. Ask what separates "ADU" from "recreational vehicle" in your specific jurisdiction's code, since the terms aren't used identically everywhere.
3. Talk to us about which model and installation fits what you're trying to do, whether that's a permitted ADU, a seasonal cabin, or something in between.