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.
Where Wolf works
In Washington and Oregon our own crews do the work. When your lot needs a survey or septic design, we line that up too. Full details →
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. Outside those two states, Wolf builds and delivers the home and a local contractor finishes the site work.
What Wolf builds
What “prefab ADU” means at Wolf
Homes are framed, wired, plumbed, and finished in Battle Ground. State inspectors from Washington Labor & Industries or Oregon’s Building Codes Division check the work in the factory. 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
Permitting typically takes 1 to 9 months. Factory construction takes 2 to 3 weeks once your production slot begins. Delivery and setup take 12 to 16 weeks. These are stage allowances and can overlap. 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.
Models
Prefab ADU starting points
Every Wolf model is factory-built. These three are the usual accessory-dwelling starting points.
Look for the rooms and details you’d actually use. We’ll review your property before recommending a layout.
Near our factory
Building an ADU in Clark County?
Our factory is in Battle Ground. Explore plans, local project stories, and planning information for your area.
ADU builder serving Vancouver
Backyard homes, city and county planning, and local project stories.
ADU builder serving Camas
Hillside and neighborhood lots, city or county planning, and floor plans.
ADU builder serving Washougal
In-town and Gorge-edge lots, local permitting, and model comparisons.
ADU builder serving La Center
City and county planning for in-town lots and rural properties.
ADU builder serving Ridgefield
Models, local planning, and nearby Wolf projects.
ADU builder serving Battle Ground
ADUs built at our local factory, with tours and a look at the process.
Questions
Frequently asked questions
What is a prefab accessory dwelling unit?
Should you get a prefab ADU?
Is a prefab ADU the same as modular?
Will my city re-inspect the factory work?
Is a prefab ADU the same as a modular or detached ADU?
How is this different from a tiny home on wheels?
Is a prefab ADU cheaper than a site-built ADU?
Are prefab ADUs energy efficient?
Keep reading
Related Wolf pages
See if your property qualifies for a prefab ADU
Send the address and intended use. We will review prefab delivery, site access, utilities, and the local placement permit.
Talk with Kelsey, Kirsten, or Lars. They’ll look at your property and answer questions until the choice is clear.
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