Washington State
ADU (accessory dwelling unit) in Washington
Washington owners usually add an ADU for family housing, rental income, or property value. Zoning, permits, access, and utilities decide whether it works. Wolf builds code-compliant ADUs in Battle Ground and delivers them across Washington. HB 1337 set statewide minimums inside urban growth areas, but your city or county still issues the permit.
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.
Who it’s for
Who a Washington ADU can work for
Families adding space for a parent or adult child
A detached backyard home is a legal second household, and the primary house stays as it is.
Owners planning long-term or (maybe) short-term rental
Inside many UGAs, owner-occupancy is no longer a statewide ADU mandate. Short-term lodging is still a local license. Bring the address.
People in Seattle, Vancouver, Olympia, Spokane, and beyond
Turn-key service, including Wolf site work, covers all of Washington and Oregon. Idaho is special-plan only, and a local contractor handles site work there. Other deliveries about 1,000 miles out are quoted when local modular rules allow. Wolf builds and delivers modular homes for select California projects, and they take more work than a Washington or Oregon job. Title 24 adds its own energy review, and the Title 24 filing must list an outside contractor. We don’t have a standing HCD-approved model, so the drawings for each California home go through HCD approval on their own. You also need a qualified local contractor for the site work, and lining one up is part of planning the project. We price and schedule each California home on its own. We have delivered homes to Santa Rosa and Petaluma in Sonoma County and to St. Helena in Napa County. See Locations for city-by-city notes.
What Wolf builds
What Washington law changed
House Bill 1337 (2023 session law; https://lawfilesext.leg.wa.gov/biennium/2023-24/Pdf/Bills/Session%20Laws/House/1337.SL.pdf), now mainly RCW 36.70A.680 and 36.70A.681 (https://app.leg.wa.gov/RCW/default.aspx?cite=36.70A.681), sets floors that Growth Management Act cities and counties cannot go below inside urban growth areas: at least two ADUs per qualifying lot, no local size cap below 1,000 gross square feet, no owner-occupancy mandate, height protected to 24 feet unless the principal home is already lower, and impact fees capped at 50 percent of the principal unit. Those protections are strongest inside UGAs. Rural lots follow county rural-ADU rules and often septic capacity. Washington L&I inspects factory-assembled structures (https://www.lni.wa.gov/licensing-permits/manufactured-modular-mobile-structures/modular-other-mobile-structures/). We confirm the rules that apply to your parcel.
Factory insignia plus local placement
L&I inspects the module. Your city or county inspects the foundation, setbacks, and utility connections, and the two can move forward at the same time.
Models that fit Washington lots
Plans run 307–1,232 sq ft. Most backyard ADUs are Model K (432) or E / F (616). Larger UGAs can take J, L, or I when coverage and delivery allow.
Cost ranges from existing site facts
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. Your complete project is quoted after reviewing the property and confirming the scope. Delivery and installation are quoted for your address and confirmed in your written scope. Permitting service and local fees are confirmed in your agreement.
Process
How a Washington ADU project moves forward
- 1
What it is
An accessory dwelling, which can be attached or detached under state law. Wolf builds detached factory homes and sets them on a permanent foundation.
- 2
When it is legal
The lot must allow an ADU under state and local rules. We confirm whether it is urban or rural, review the local overlay, and flag any HOA (homeowners association) restrictions tied to the address.
- 3
Typical size
State law stops jurisdictions from forcing an ADU smaller than 1,000 sq ft inside UGAs; they can allow larger. Wolf’s published plans run 307–1,232 sq ft, and choosing a smaller one is up to you.
- 4
What Wolf handles
Wolf employees handle the project from evaluation and permits through factory construction, foundation, delivery, utility connections, and installation, with third-party specialists when required.
Models
Washington ADU starting points
Choose a larger plan when the property can support it and the extra bedroom or bathroom serves a clear need.
Notice the rooms and details you would use. These are layouts to explore; we need to review your property before recommending one.
Questions
Frequently asked questions
Do I have to live on the property?
Can I put two ADUs on one Washington lot?
Are Wolf ADUs “pre-approved” by Washington?
Do you have guides for specific Washington cities?
Keep reading
Related Wolf pages
Washington ADU laws
HB 1337, RCW cites, and the statewide floor.
Clark County ADU rules
City vs unincorporated, UGA vs RADU, official GIS and handouts.
Locations
Cities we serve, from Vancouver to Seattle, Spokane, and the coast.
ADU builder
Factory-built accessory dwellings, from lot check to set.
ADU for rental income
Long-term rental planning, costs, and local requirements.
See what your Washington property can support
Send the address and how you would use the unit. We will check jurisdiction, UGA vs rural, access, utilities, and a model that can be permitted as a dwelling.
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