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In-home and basement ADUs in Seattle
A separate unit inside your existing house, usually in a basement or a wing, with its own entrance, kitchen and bath.
What is an in-home ADU?
In Seattle it is an attached ADU created inside the existing house. Converting existing space can go beyond the 1,000-square-foot cap that applies to new above-ground ADU floor area.
What does a basement need?
- Enough ceiling height for living space
- Egress windows or doors for sleeping rooms
- Fire separation and sound control from the main house
- Drainage and moisture control
Can I add a cottage later?
Yes. Seattle allows two ADUs on a lot, so an in-home unit now and a backyard cottage later is a common plan.
In-home units in Seattle
Washington does not use California's junior ADU category. In Seattle, a unit inside the house is an attached ADU, and converting existing space is allowed beyond the 1,000-square-foot cap.
Related
Is your lot ready for an ADU?
Send your address and a sentence about what you want. We look up the zoning, setbacks and utility routes and reply with the ADU types that fit.
We build in Seattle, WA.