ADU basics
What is an ADU (accessory dwelling unit)?
An ADU is a second, self-contained home on the same lot as a primary residence — with its own kitchen, bathroom, and entrance. People also call them backyard cottages, granny flats, in-law suites, casitas, guest houses, or DADUs (detached accessory dwelling units). Whatever you call it, it’s a complete home where someone can cook, sleep, and live on their own.
The forms it takes
Three ways an ADU shows up
The label changes with the layout, but the idea is the same: a complete, independent dwelling that shares a lot with a main home.
Detached ADU (DADU)
A standalone home in the backyard — also called a backyard cottage, granny flat, in-law suite, casita, or guest house. This is what Wolf builds: a complete little house with its own kitchen, bath, and front door.
Attached ADU
An addition that shares a wall with the main house but has its own entrance, kitchen, and bath.
Conversion ADU
A basement, garage, or attic turned into a separate living unit. It’s built inside space you already have instead of as a new structure.
ADU vs. cottage vs. tiny home
What changes is how it’s classified
“Backyard cottage,” “tiny home,” and “ADU” often describe the same building. The real difference is how your local jurisdiction classifies and permits the structure:
- A cottage / detached ADU is a permanent, foundation-set home permitted as an accessory dwelling.
- A tiny home is usually a dwelling under about 400 sq ft. On a permanent foundation it can qualify as an ADU; on wheels it may legally be an RV.
- Separate ownership depends on state and local rules and the property’s legal structure. An ADU does not automatically create a separate parcel; condominium ownership may be possible in some jurisdictions.
Wolf homes are built to the same IRC/IBC (International Residential Code / International Building Code) building codes as site-built houses and set on a permanent stem-wall foundation, so they’re permitted as permanent ADUs.
Modular ≠ manufactured
Manufactured (mobile) homes are built to the federal HUD code (the federal standard for manufactured homes). Wolf builds modular homes to the same residential building codes as stick-built houses. They’re assembled indoors in our Battle Ground factory, then delivered and set on your foundation. That’s why they appraise, permit, and live like conventional homes.
Modular vs manufactured → Tiny vs ADU vs manufactured →Can I have one?
What decides if an ADU fits your property
Eligibility comes down to your jurisdiction’s rules and your specific lot:
- Zoning & municipal code — whether your zone allows an ADU, and how many.
- Setbacks — how close to property lines a structure can sit.
- Utilities & access — where water, sewer/septic, and power are, and how a home can be delivered to the site.
- HOA (homeowners association) rules — some neighborhoods add their own requirements.
Washington limits owner-occupancy requirements for covered urban ADUs, with statutory exceptions. Rural lots need a separate local-code check. Read RCW 36.70A.680 and 36.70A.681, then confirm your parcel’s jurisdiction and constraints.
The fastest way to know
Send us your address and what you want to build. We’ll check zoning, setbacks, utilities, and access and tell you whether it’s feasible. The evaluation is free, and you don’t commit to anything.
Free Property EvaluationHow Wolf builds your ADU
One team, from your lot to your keys
For Washington and Oregon projects, Wolf coordinates property evaluation, design, permitting, factory construction, delivery, and setup. The home is built indoors in our shop and finished on site. Projects farther away receive a location-specific proposal that identifies local contractors and responsibilities.
Our permit team reviews feasibility early. If approval is not possible, your signed permitting agreement defines the eligible refund and exclusions. Review those terms before paying the permitting service fee.
Common questions
ADU questions, answered
Is an ADU the same as a tiny home or a cottage?
Can I sell an ADU separately from my house?
Do I have to live on the property to have an ADU?
Plain-English glossary
ADU terms, decoded
- ADU
- Accessory dwelling unit — a second, self-contained home on the same lot as a primary residence, with its own kitchen, bath, and entrance.
- DADU
- Detached accessory dwelling unit — a free-standing ADU, i.e. a backyard cottage.
- Backyard cottage / granny flat / in-law suite / casita
- Common nicknames for the same thing: a detached ADU.
- Tiny home
- Usually a dwelling under about 400 sq ft. On a permanent foundation it can qualify as an ADU; on wheels it may legally be an RV instead.
- Setback
- The minimum distance a structure must sit from property lines — a key factor in whether (and where) an ADU fits on your lot.
- Stem wall
- The short supporting wall that joins the foundation to the structure above. Wolf homes are set on a concrete stem-wall foundation.
- Mini-split
- A ductless heat-pump system that both heats and cools — the primary climate system in a Wolf home.
- Turn-key
- Wolf handles the whole project — permitting, production, delivery, and site work — so you’re left with cosmetic choices like paint colors, not a construction project to manage.
- System development charge (SDC)
- A one-time jurisdiction fee for connecting to public utilities and services. It’s often the single largest line in your permit fees.
- Modular vs. manufactured
- Manufactured (mobile) homes are built to the federal HUD code. Wolf builds modular homes to the same IRC/IBC building codes as site-built houses — they’re real, permanent dwellings.
Think your backyard has room for an ADU?
Send us the address and the goal. We’ll tell you what fits, what it takes to permit, and what an all-in project looks like.
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