Support without enabling forever
Your kid can't afford this market, and you don't want to watch them fail — or move them back into their childhood bedroom. A backyard unit gives them real independence with a wall in between, and becomes a rental when they launch.
The tension here is specific: “I don't want to enable them forever, but I can't watch them fail in this market.” Parents describe being caught between being supportive and fostering dependence. The common refrains — “my kid can't afford anything in this city,” “they're paying $1,800 for a studio with roommates,” “they need to feel independent” — all point to the same fix: physical separation that preserves psychological boundaries.
The situation
Seattle market rent is the squeeze. A 1-bedroom runs $1,800+/month, which is why so many young adults end up with roommates or back at home. Moving back into their old bedroom collapses the boundary for everyone. A separate unit in the backyard does the opposite: their own front door, their own space, their own routine — close enough for support, far enough for both of you to have a life.
The cost case
Think of it as the difference between subsidizing a landlord and building an asset. Whatever you'd otherwise spend helping with rent stays on your own property. And when your child launches, the unit doesn't go away — it becomes income.
| Format | Build cost (King County) | Later rents for |
|---|---|---|
| Garage conversion | $80K–$350K | $1,200–$2,200/mo |
| Basement AADU | $225K–$475K | $1,200–$2,500/mo |
| Detached DADU | $250K–$700K+ | $1,600–$3,500/mo |
Which format fits
For a single young adult, the lower-cost formats usually make the most sense. A basement AADU ($225K–$475K) keeps them under the same roof with a separate entrance — good for a transitional stretch. A detached DADU ($250K–$700K+) costs more but gives the most independence now and the highest rent later, which matters because of the one feature that defines this use case:
Build for the conversion.The whole point is a graceful handoff from family use to market rental. That means a full unit — real kitchen, separate entrance, its own electrical and HVAC — not a glorified bedroom. Under HB 1337 you're free to charge your child no rent, a modest rent, or market rate; whichever you pick, building to a rentable standard keeps every option open.
Keep reading
Is an ADU worth it in Seattle? → covers the full math, including the eventual rental case. Compare the formats on the DADU → and basement AADU → pages, then check your lot → for a planning cost range and what your city allows.
Generally you can house family in your ADU without charging rent — it's your property to use. Gift, support, and tax questions depend on your situation, so confirm specifics with your accountant or attorney. This page is about the build decision, not tax advice.
