Don’t Say Tiny Home – Washington’s Confusing Terminology

You’ve decided you want to build a tiny home. Wonderful. The first logical step is to figure out how to do it right — follow the permitting guidelines, talk to the right agencies, get your build done properly. So you open a browser and start researching.

Two hours later you are more confused than when you started. What does Washington’s Labor and Industries department have to do with this? Is a tiny home the same as a tiny house? Is it an RV? Do I need a contractor’s license? Why does one page say to call the local building department and another says to call L&I and another says to call both?

Here’s the core of what’s happening: Washington State uses the term “tiny home” in its official documentation, but what the state means by that term is almost certainly not what you mean. Getting that distinction straight before you make any phone calls will save you a serious amount of confusion.

What Washington State Means by “Tiny Home”

L&I’s website defines a tiny house as “a dwelling that may be built on wheels and is no larger than 400 square feet, including a kitchen, bathroom, and sleeping/living area” that “must be built to the Washington State Building Code.”

Read that again: built to the Washington State Building Code. That’s the residential construction standard — the same code that governs stick-built houses. L&I’s tiny house program is essentially a factory-built structures program for very small residences. If you build a 380-square-foot home in a factory or a backyard and then transport it to where it will be permanently placed, L&I reviews the plans and conducts inspections during construction. When it’s done, they put an insignia on it — a metallic gold label certifying compliance — and it goes to its permanent site as a finished dwelling.

This is a legitimate and useful category of housing. The structure gets designed to residential code, inspected like a residential structure, and ultimately sited like one. The fact that it traveled on wheels to get there doesn’t change what it is: a small house.

But here’s where almost everyone goes wrong. When most people say “tiny home,” they are not talking about this. They are talking about something built to an entirely different standard, governed by an entirely different set of rules, and used in an entirely different way.

What Most People Mean by “Tiny Home”

What most people mean is a tiny home on wheels — a THOW. And a THOW, despite the name and despite what you might read on various websites, is not built to residential code. It is built to RV standards.

A recreational vehicle is designed primarily for mobility and temporary occupancy — road trips, camping, seasonal use. Standard RVs are built to NFPA 1192, the RV Industry Association’s safety standard. How they are regulated depends on the state: some handle it through the DMV, while Washington regulates them through L&I’s separate recreational vehicle program. They require registration, tags, and insurance like any vehicle.

A tiny home on wheels is, in the eyes of regulators and most building codes, an RV. It travels on a trailer frame. It gets registered as a vehicle. It is certified to RV or park model RV standards — RVIA, RVIC, ANSI A119.5, or NOAH — not to residential building code. L&I inspects and regulates these units too, but through an entirely different program than the tiny house program described above.

This is the distinction that the L&I website gestures at but doesn’t make quite clearly enough. Under the “About Tiny Houses” tab, after defining a tiny house as a sub-400-square-foot dwelling built to residential code, L&I adds this note:

“If you’re building a structure with wheels, that’s not a tiny house as described above, then you may be building a recreational vehicle or park model. We inspect and regulate these units.”

So L&I regulates both. But they are completely separate programs, with completely separate standards, and completely separate outcomes for where and how you can live in the result. The casual reader — and even the careful one — can easily miss this and spend weeks researching the wrong category.

The IRC Appendix: A Third Layer of Confusion

To make things more interesting, there’s a third thing that sometimes gets called “tiny home” in regulatory contexts: structures built under Appendix Q of the International Residential Code.

The IRC is the model residential building code that Washington and most states adopt (with modifications) as their base standard. For most of its history, the IRC effectively prohibited very small dwellings by requiring minimum ceiling heights, room sizes, and stair configurations that a 200-square-foot structure simply couldn’t meet. Appendix Q was added to address this — it relaxes those requirements specifically for dwellings under 400 square feet, allowing loft bedrooms with lower ceiling heights, alternating-tread stair devices, and other design accommodations that only make sense at small scale.

This matters because just permitting a permanently sited residential structure under 400 square feet is itself a relatively new development in building code. Appendix Q made it possible to build a code-compliant, permitted, foundation-sited tiny house without having to fight the code on every unconventional detail.

But Appendix Q has nothing to do with tiny homes on wheels. It is a residential code provision for residential structures. A THOW built to RVIA or NOAH standards is not designed to Appendix Q, doesn’t get inspected to Appendix Q, and isn’t sited under Appendix Q. If you’re talking to an official and you mention Appendix Q, they will assume you’re talking about a foundation structure. If you’re actually building a THOW, that’s the wrong conversation.

The Practical Guide: What to Say to Whom

So here’s the translation guide for navigating Washington State:

If you are building a small house that will be permanently placed on a foundation or a site — one that travels on a trailer only to get there and never moves again — you are probably in L&I’s tiny house program. It will be built to residential code (IRC/Washington State Building Code), L&I will inspect the construction if it’s built offsite, and your local building department will handle the siting permit. When you talk to officials, say “tiny house” or “factory-built residential structure under 400 square feet.” Do not say “tiny home on wheels” or “THOW” — they will route you to the wrong program.

If you are building something that will live on a trailer frame, be registered as a vehicle, and potentially move from site to site — the kind of thing that parks in an RV community, a backyard, or a rural property — you are building a tiny home on wheels. It will be built to RV standards (RVIA, NOAH, ANSI A119.5, or similar), registered and titled like a vehicle, and governed at the siting level by local zoning and RV park regulations. When you talk to officials, say “tiny home on wheels,” “THOW,” or simply “recreational vehicle.” Do not say “tiny home” or “tiny house” — you will end up in a conversation about residential building code that has nothing to do with what you’re building.

This second point extends beyond the building process. If you are talking to a city planner, a county zoning official, a building department, or a property owner about where you want to live, use the term RV or THOW. “Tiny home” will trigger a residential housing conversation. “RV” or “tiny home on wheels” will trigger the recreational vehicle conversation, which is the one that actually applies to your situation and will get you accurate information about what’s allowed where.

Why This Matters More Than It Should

None of this confusion is anyone’s fault exactly. The term “tiny home” entered popular culture to describe a lifestyle and an aesthetic — small, intentional, mobile living — and it stuck. Regulators then had to figure out how to categorize these structures using existing legal frameworks, and different agencies landed on different answers. L&I used “tiny house” to describe their factory-built residential program. The RV industry uses RVIA certification for structures that look identical to what Instagram calls a tiny home. Nobody coordinated the terminology.

The result is that a phrase everyone uses to mean roughly the same thing — a small, thoughtfully built living space — means completely different things to the people who regulate it. The structure of the state’s own documentation reflects this: L&I’s tiny houses page mentions “built on wheels” in its definition and then, a few lines later, notes that if you’re building a wheeled structure, that’s actually a different program entirely.

If you’re working through what a THOW build involves in Washington — what it gets built to, where it can legally go, and what the process actually looks like — get in touch. This is what we do.