Washington Statewide Rule

Washington Tiny House Standards Under State Building Code

Few RestrictionsApplies statewide across Washington (2026)

Key Facts

On-foundation standard: IRC Appendix Q
Max size (Appendix Q): 400 square feet
Wheeled tiny house: Dwelling built to building code
Community statute: RCW 35.21.686

Last verified: September 5, 2026Source: Washington State Legislature

Summary

Washington allows tiny houses on permanent foundations under IRC Appendix Q (adopted in the state building code) for dwellings 400 square feet or less. RCW 35.21.686 governs tiny houses with wheels and tiny house communities.

(2) The owner of the land upon which the community is built shall make reasonable accommodation for utility hookups for the provision of water, power, and sewerage services and comply with all other duties in chapter 59.20 RCW.

Source: Washington State LegislatureView official code

Full Breakdown

Washington adopts IRC Appendix Q for tiny houses on permanent foundations of 400 square feet or less through chapter 51-51 WAC, providing relaxed ceiling-height and loft standards. RCW 35.21.686 defines a tiny house and a tiny house with wheels as dwellings built to the state building code, and it authorizes cities to regulate tiny house communities. It also bars a city from adopting an ordinance that prevents entry or requires removal of a tiny house with wheels used as a primary residence in manufactured or mobile-home communities. Zoning and density rules otherwise still apply.

Violations & Penalties

Local rules that exclude a tiny house with wheels used as a primary residence in a manufactured or mobile-home community are limited by RCW 35.21.686.

Frequently Asked Questions

Are tiny houses legal in Washington?

Yes. Tiny houses on foundations are built under IRC Appendix Q, and RCW 35.21.686 defines tiny houses with wheels as dwellings built to the state building code.

Can cities ban tiny house communities?

RCW 35.21.686 lets cities regulate tiny house communities and bars them from excluding a tiny house with wheels used as a primary residence in manufactured or mobile-home communities. Zoning still applies.

Sources

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