Washington has rules for tiny homes, but where you can actually live in one still depends on your county. Here’s how the state law works, what L&I requires, and what local zoning allows.
State Rules: What Washington Actually Recognizes
Washington is one of the few states that officially defines a tiny home in law. The Department of Labor & Industries (L&I) oversees construction and certification for factory-built units. A tiny house is any dwelling 400 sq ft or smaller, built either:
On wheels (THOW) — regulated under ANSI A119.5 / NFPA 1192 standards for RVs, or
On a foundation — built under the International Residential Code Appendix Q.
If a unit is built off-site (in a factory or by a third-party builder), it must pass L&I plan review and inspection before it can be sold, delivered, or permitted.
Source: Washington L&I — Tiny Homes Overview
Senate Bill 5383: The Legal Backbone
In 2021, the Washington Legislature passed SB 5383, protecting the right to use tiny homes and RVs as primary residences in manufactured or mobile-home communities. It prevents cities or towns from banning them outright within those zones.
But there’s a catch:
SB 5383 does not require local governments to allow THOWs on private residential lots, agricultural land, or vacant property. Cities and counties still control where and how you can live in one.
Reality Check: The County-by-County Maze
State approval doesn’t equal blanket permission. In practice, zoning and occupancy rules vary dramatically:
Many counties still classify THOWs as temporary dwellings—often capped at 90 days continuous occupancy or restricted to seasonal (“snowbird”) use.
Some require that the tiny home share a lot with a permanent residence (used as an ADU or guest suite).
Roof pitch, setbacks, and utility codes differ by city. Even a legal THOW may need a steep-roof design or a sewer connection to qualify.
Insurance can also be tricky—some carriers treat movable units like vehicles rather than homes.
So before buying land or parking a tiny home, check with:
Your county planning office for zoning and land-use codes.
Your building department for required permits or occupancy limits.
L&I if your builder needs a factory-built housing label.
Even within the same state, King County, Spokane County, and Port Townsend have entirely different approaches.
Local Examples
King County
Recognizes tiny homes as detached dwellings, but off-site builds must carry L&I certification before local permits are issued.
Utility hookups and septic approval are mandatory for permanent placement.
Source: King County Residential Tiny Homes Guide (PDF)
Port Townsend
One of Washington’s most tiny-home-friendly cities. Allows Tiny Houses on Wheels in commercial zones (C-II, C-II S) under clear design standards—licensed, road-ready, ANSI-certified, with full hookups and spacing from adjacent dwellings.
Source: Port Townsend Municipal Code § 17.58.040
Spokane County
Adopted Appendix Q, allowing foundation-based tiny homes under IRC standards in certain residential and rural zones.
Source: SpokaneCounty.gov
Getting Legal: Steps for Homeowners
Check your zoning first. Is your parcel inside city limits, or county rural?
Confirm utility access. Full water, sewer, and electrical hookups are typically required for long-term occupancy.
If your home is factory-built, get L&I approval. You’ll need that insignia before any local inspection.
Verify occupancy limits. Some jurisdictions still restrict year-round living in movable dwellings.
Keep it movable and compliant. Licensed wheels, skirting, and certified electrical systems help avoid reclassification issues.
Washington has clearer rules than most states for tiny-home construction—but not for full-time living everywhere. Your build can be perfectly legal under L&I yet still illegal to occupy, depending on local zoning.
Do your homework, get it inspected, and confirm your county’s stance before committing to land or a build.
Once you’ve got the green light, the next step is choosing a builder who already meets Washington’s factory and ANSI standards.
Check out our companion guide to the Top Tiny Home Builders in Washington to find certified builders serving the Pacific Northwest.