Prefab ADUs

Prefab ADU (accessory dwelling unit) Builder

Prefab describes a home that is partly or fully assembled away from the property. Wolf builds modular homes to residential IRC/IBC (International Residential Code / International Building Code) code, has them inspected in the factory, and installs them on permanent foundations.

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Where Wolf works

In Washington and Oregon, Wolf employees handle your project from property review and permits through construction, site work, delivery, and installation. Some projects require third-party services, such as surveys or septic design and installation, depending on the property and jurisdiction. Beyond Washington and Oregon, local contractors complete site work and utility connections.

Finished Wolf Industries Model E two-bedroom modular ADU on a Pacific Northwest lot

Who it’s for

Why homeowners choose a prefab ADU

Owners adding a rental, guest space, or family dwelling

You want a complete second unit with its own kitchen, bath, and door, without a year of framing in the side yard.

People comparing prefab vs stick-built vs HUD (the federal standard for manufactured homes)

Prefab means built off-site. Modular is residential code. Manufactured is HUD code on a chassis. Those three finance, insure, and permit differently.

Anyone who still has to pass a local placement permit

Factory inspection covers the module. The city or county still reviews the foundation, placement, utilities, and final site work.

Owners who want the structure out of the weather

Western Washington and Oregon are wet from fall through spring. Framing, wiring, insulation, and finishes happen indoors instead of under a tarp in your yard.

People who want the home price early

Each model page shows the starting price for the home itself. Site work, utilities, and local fees are priced after we review the property, and the proposal lists each line separately.

Families who need one accountable team

In Washington and Oregon, Wolf employees handle evaluation, permitting, factory construction, site work, delivery, and installation, with third-party specialists when needed. You work with Wolf throughout.

What Wolf builds

What “prefab ADU” means at Wolf

Homes are framed, wired, plumbed, and finished in Battle Ground under state factory inspection by Washington Labor & Industries or Oregon Building Codes Division Prefabricated Structures. They leave the factory about 92% complete with a state insignia. Local inspectors then focus on the foundation, placement, and utilities. Our models range from 307 to 1,232 sq ft, with prices for the homes themselves ranging from $67,500 (Model B, available only in the City of Portland) to $178,500 (Model I). Your complete project is quoted after reviewing the property and confirming the scope.

Pre-engineered models

Proven plans keep a small home easier and faster to permit. Finishes and some layout options come from the Options Book.

Turn-key on the property side

Wolf employees handle evaluation, permitting, factory construction, site work, delivery, installation, and a one-year workmanship warranty, with third-party specialists when required.

Typical timeline

Shop production is typically three to four weeks once the home is in line. Permitting often runs two to nine months, because a prefab home still goes through local review.

Process

Can you legally place a prefab ADU here?

1
What it is

A factory-built accessory dwelling set on a permanent foundation. On most residential lots the land-use name is ADU.
2
When it is legal

When zoning allows a second dwelling and the lot can take setbacks, coverage, parking, and delivery. Washington UGAs follow HB 1337 floors; Oregon UGB cities follow ORS 197A.425. Rural lots and HOAs can differ.
3
Typical size and cost

Most backyard prefab ADUs are Model K (432 sq ft) or Model E/F (616 sq ft). Prices for the homes themselves range from $67,500 (Model B, available only in the City of Portland) to $178,500 (Model I), with appliances separate. Installation and site work are quoted for your property. Permitting service and local fees are confirmed in your agreement.
4
Permit path Wolf handles

Free evaluation → proposal → local placement permit in parallel with factory insignia → stem-wall foundation, crane or trailer set, hookups, occupancy.

Full process ADU rules & guides

Models

Prefab ADU starting points

Every Wolf model is factory-built. These three are the usual accessory-dwelling starting points.

Notice the rooms and details you would use. These are layouts to explore; we need to review your property before recommending one.

Model K — 432 sq ft

One-bedroom prefab ADU for guest or rental use.

Model E — 616 sq ft

Two-bedroom prefab ADU with a defined living room.

Model L — 984 sq ft

Larger cottage-scale modular home when the zone allows it.

Compare the models

Questions

Frequently asked questions

What is a prefab accessory dwelling unit?

A prefab accessory dwelling unit is a second home on your lot that is built mostly off site, then delivered and installed. At Wolf, that means a modular home built to residential code with a full kitchen and bathroom, inspected in the factory, and set on a permanent foundation. It can house family, guests, a caregiver, or a long-term tenant where local rules allow.

Should you get a prefab ADU?

A prefab ADU makes sense when you want a complete second home, your lot can take a delivery trailer or crane, and you would rather have the structure built indoors than framed in your yard. It may not fit if you want a garage or basement conversion, if no delivery route can reach the site, or if you want a fully custom design. A free property evaluation answers the lot questions first.

Is a prefab ADU the same as modular?

Prefab is the broader term. Wolf modular homes are factory-built to residential code and set on a permanent foundation. That is not a panelized kit or a HUD manufactured home.

Will my city re-inspect the factory work?

Generally no for the sealed structure. Local inspectors focus on foundation, placement, and utility connections. Follow what your jurisdiction publishes.

Is a prefab ADU the same as a modular or detached ADU?

Prefab describes how the home is built: in a factory, then delivered. Wolf’s prefab ADUs are modular homes, and most are detached from the main house. See modular ADUs and detached ADUs if those terms match what you are planning.

How is this different from a tiny home on wheels?

A Wolf ADU is permitted as a permanent dwelling on a foundation. A trailer used as housing generally goes through a different permit path, and Wolf homes are not RV-rated.

Is a prefab ADU cheaper than a site-built ADU?

Not automatically. The price of the home itself is known up front, and indoor production keeps weather delays off the structure. Site work, utility fees, and permitting still depend on the lot and can be a large share of the total. We quote the whole project. See what a Wolf ADU costs.

Are prefab ADUs energy efficient?

Wolf homes are all-electric, with a ductless mini-split heat pump, ERV (energy recovery ventilator) ventilation, double-pane low-E windows rated U-0.27, and insulation installed in the factory. Actual utility bills depend on the climate, the model, and how you run the home.

Keep reading

Send the address and intended use. We will review prefab delivery, site access, utilities, and the local placement permit.

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