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May 30, 2026
Tiny Home Design in Seattle: What Is Legal, What It Costs, and Who It Is For
Tiny homes have captured public imagination as an affordable housing solution — but their legal status in Seattle is more nuanced than most coverage suggests. Here is a practical guide.
What Is a Tiny Home?
“Tiny home” is not a regulatory term. Depending on the design, a tiny home might be classified as:
- A detached ADU (if on a permanent foundation, meets minimum size, and complies with residential code)
- A manufactured home (if built to HUD standards in a factory)
- A recreational vehicle (if on wheels — and therefore not permitted as permanent housing in Seattle)
What Is Legal in Seattle
Seattle does not have a minimum size limit for ADUs, meaning a legally constructed ADU can be very small — even 200-300 sq ft — as long as it meets all other code requirements (ceiling height, egress, habitability, energy code). This is the legal path to a “tiny home” in Seattle: build it as a DADU that meets code.
Tiny Homes on Wheels (THOWs)
THOWs are classified as RVs in Seattle and are not permitted as permanent residential housing on private property. They are only legal in designated RV parks — of which Seattle has very few.
Cost of a Small ADU in Seattle (2026)
- 200-400 sq ft detached ADU on permanent foundation: $130,000-$250,000
- Architect design fees: $15,000-$28,000
Who Should Consider a Small ADU
Homeowners with limited lot space or budget who want to add rental income or multigenerational living. Small ADUs have strong rental markets in transit-adjacent neighborhoods.
Piper Cole Architects designs small and efficient ADUs. See our ADU service or contact us — call 425-753-6452.
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