Washington state requires that tiny houses on wheels be compliant with ANSI 119.2 for RVs or ANSI 119.5 for park models RVs. However, you don’t need to be RVIA for certified. You may be able to “self-certify” if you can supply a comprehensive set of plans for your tiny house and demonstrate that you have a quality control program.

http://apps.leg.wa.gov/rcw/default.aspx?cite=43.22.355

Steps for registering a tiny house in Washington State: http://www.wsp.wa.gov/traveler/docs/cvd/170_129.pdf

Washington state