Tiny prefab homes: Understanding the classifications

Welcome to our shop here in Battle Ground, WA. This is where we build and install high-performing small modular homes that go on permanent foundations. People define “tiny home” in different ways, so we want to be clear about what we build. There are a lot of other housing options out there, too. So it helps to peel back a few layers and get a better grasp on what we’re really talking about.

I first went looking for a small rental cottage that I could legally keep on wheels and pull from place to place. The first home I built was a typical uninspected unit on an old mobile home frame. It rented out quickly, and I realized there was high demand for a rental like that. As I dug deeper, I found that we’d need a legal, permittable option if we were going to build these tiny prefab homes at scale. Plus, I was nervous about what the regulators and code officials would say about my product.

That first one gave us a rough experience. A customer wanted to place one of our homes on a small downtown lot in Vancouver, WA. The neighbors were pretty upset about a tiny prefab home in the backyard next door. Naturally, they called code enforcement and made a complaint. We had to remove the home so our client wouldn’t have to deal with the barrage of issues that comes with code enforcement.

Using that experience as a springboard, we hit the books and the internet. We scoured everything we could find on these topics:

• Tiny homes on wheels (THOW)
• RVs
• Park model RVs
• FEMA trailers
• Mobile homes
• Manufactured homes
• Modular homes
• Temporary worker housing
• IBC (International Building Code)
• State codes
• Local codes
• Zoning and land use codes
• Classification of structures and what each one means

We spent thousands of dollars and close to three months pounding the pavement, trying to sort through this huge pile of information. The same answer kept coming back: it needed to be a structure built for long-term living. To give our clients stability and confidence, we had to find a better way to keep the regulators out of their backyards. We believe we’ve done just that.

Let’s go over the different options, with the pros and cons of each.

Tiny homes on wheels

These are the craze right now, if you go by public opinion. They’re cute, classy, and full of unique custom designs, and they draw people in by the droves. There are tiny house tours, tiny house hotels, tiny house trade shows, tiny house TV shows, and the list goes on.

The downsides don’t get talked about as much. Better materials mean much heavier towing loads. The bed placement can be awkward, which is tough for aging seniors. They’re an expensive value proposition, and you can’t live in them long term. Parking and financing are both hard. Plus, tiny homes on wheels usually don’t have an RV certification.

RVs

Most people know an RV when they see one.

The roof shape is usually designed for easier travel down the road. RVs have holding tanks for both gray water and black water, and they usually run on 12-volt power systems. They’re also designed to be as light as possible.

The real dividing line is the RVIA certification. An RV gets hooked up to temporary utilities and isn’t designed for long-term living, though people do live in them for long stretches. In the end, the 2” walls and skimpy insulation make for a tin box that sweats with the weather outside.

Park model RVs

These are built and inspected to a different code, ANSI (American National Standards Institute) A119.5. They have their own classification and must be less than 400 sq ft. That’s measured from the outside of the siding on one side to the outside of the siding on the other. They’re usually placed in RV parks as cabins. They aren’t attached to the ground with a foundation system.

Park model RVs don’t meet the energy code for most states. They’re meant for short-term vacation use. They don’t have the structural rules that regular buildings do, even though many of the materials are similar.

FEMA trailers

This is a loose term I picked up because I’ve heard people use it. In my experience, a “FEMA trailer” is an RV, a park model RV, or one of the other types further down this list.

When a disaster strikes, FEMA needs to supply some sort of temporary housing. So it turns to the factories that already exist. FEMA isn’t going to reinvent the wheel for a short-term problem.

Mobile homes

These are built to HUD (Housing and Urban Development) standards, which are set at the federal level.

From my research, they haven’t been built since 1976. That’s when the HUD code (the federal standard for manufactured homes) was standardized. After 1976, you had to meet certain plumbing, electrical, thermal, and frame requirements. After 1976, the manufacturers also changed the name of what they were making to match what the market wanted. They started calling them manufactured homes.

Manufactured homes

This is the official era of the HUD home. Every structure built after 1976 to the federal HUD standards is considered a “manufactured home.” The interesting part is how the public sees these homes. To most people, anything built in a factory is “manufactured.”

It really comes down to what’s on the inspection tag. Every factory-built structure has a tag that shows what codes it was built to and which inspection agency approved it.

Manufactured homes can be built on a steel trailer frame chassis and temporarily strapped to the ground. They can also be placed on permanent foundations, but that isn’t the norm. For more, read modular vs. stick-built vs. manufactured homes.

Temporary worker housing

This is a section of Washington’s Administrative Code, Chapter 296-833. It spells out what can and can’t be offered to workers who are housed on the job site. It usually applies to farm work, mining, or any other line of work where it makes sense to house workers.

This code section doesn’t say what code or standards the homes have to be built to, other than that they need to be legal. For example, a guest house, shed, or outbuilding can be built to legal standards and might even have a kitchen. But if it doesn’t give workers a place to wash their clothes, it’s out of compliance and has to be fixed.

For specifics, look up the local codes and requirements for this kind of housing.

Modular homes

These homes are built in a factory, and people sometimes confuse them with manufactured homes. But they’re very different. Again, it comes back to what code they’re built to and who inspected them.

Modular homes are built to the local building codes for the place where the home will sit. Most of the time, these homes sit on a permanent foundation. They can come in one unit or many, depending on the size of the project. An average home is usually two units, up to a maximum of five.

Modular is also used in large commercial projects. Guerdon Modular Buildings in Idaho, for example, will build an entire hotel out of 100+ boxes, as we call them in the industry.

Here at Wolf, we started with single-box modular homes. Today most of our models are still single-section, and the larger plans arrive in two or more sections.

IBC, IRC (International Residential Code), NEC, UPC, UMC, WSEC, and many other codes

Most codes are set at the national level. Then each state adopts and amends them to fit its local needs and site conditions. The building code is broken into many smaller sections, so experts in each field can develop, maintain, improve, and manage their part. The main acronyms stand for:

• IBC: International Building Code
• IRC: International Residential Code
• NEC: National Electrical Code
• UPC: Uniform Plumbing Code
• UMC: Uniform Mechanical Code
• WSEC: Washington State Energy Code

Keep these codes in mind as you plan a new home, because they decide what makes a building safe and livable. The codes on their own can be daunting to understand and work within. On average, every three years the council for each code section reviews suggested updates, then rolls out the changes the next year. Of course, this is a very high-level view. Any dwelling, studio, cottage, structure, guest house, hardship dwelling, and so on has to meet these codes.

In the end, we needed a product that could scale and meet the demand for affordable long-term housing. The most logical choice was the modular option that met all the local, state, and federal codes. That’s what we did.

The rest of this series covers permitting, building, living in, and maintaining a tiny prefab home, small structure, or cottage. Keep going with Building small, part 1.