Planning an accessory dwelling unit

ADU feasibility in Washington

An ADU is a second dwelling on land you already own. The floor plan is the last question, not the first.

Request a consultation Explore ADU design ideas

Washington cities implement statewide ADU policy with local zoning, permits, and inspections. What is allowed in Redmond is not automatically allowed in Seattle, Spokane, or Vancouver. Confirm the city that has jurisdiction over the lot.

This is a planning article. Use it to pressure-test the property before you invest in detailed drawings.

Detached backyard ADU designed for a Pacific Northwest property — ADU design inspiration. Editorial gallery photography, not a completed RT Signature Homes project and not a permitted plan for your lot.

The feasibility list

1. Zoning and dimensional rules. Size, height, setbacks, lot coverage, parking, and whether detached, attached, or conversion is even on the table.
2. Access. A legal, livable way in and out that does not wreck the main house.
3. Utilities. Water, sewer or septic, power, stormwater. Upgrades can decide the project.
4. Structure. Garage conversion, basement conversion, addition, or new detached building each carry different investigation.
5. Use. Family, rental, office, and guest use change layout, parking, and sometimes review.
6. Neighbors and privacy.Windows, decks, and entries land on someone else's life.

If any of those are unknown, a pretty studio rendering is fiction.

Redmond as an example, not a statewide rulebook

RT Signature Homes is based in Redmond at 4164 148th Ave NE. For a Redmond lot, the City of Redmond is the permit authority. Fee math and submittals follow Redmond's published process, not a statewide template. See What remodel permits can cost in Redmond and the city's development services fees.

For Seattle and Eastside lots, start with the nested service page: ADU builder in Seattle and the Eastside. That page is the market-and-service owner. This article stays on how to pressure-test a lot anywhere in Washington.

Seattle, Redmond, and Bellevue do not share one ADU checklist. Confirm current standards with the city that has jurisdiction during the project, not from memory.

What we will not do in this article

Invent a turnkey ADU price
Treat design-gallery photography as finished RT ADUs
Tell you your lot is approved

How a consultation uses this list

Bring the address, how you want the unit used, and any survey or prior drawings you already have. The first conversation is about whether the lot, the household, and a design-build path are a fit. It is not a permit decision and not a construction agreement.

Questions homeowners ask

Can every Washington lot take an ADU?

No. Feasibility is property-specific.

Is a garage conversion easier than a new detached building?

Sometimes, sometimes not. Foundation, ceiling height, structure, moisture, insulation, egress, utilities, and parking rules all have to be evaluated.

Do I start with a floor plan?

Start with zoning, access, utilities, and use. The floor plan comes after those are known.

Who issues the permit?

The city (or county) that has jurisdiction over the lot. RT Signature Homes coordinates permitting as part of qualifying design-build work. We do not replace the city's rules.

Continue exploring