Whatcom County, WA Accessory Structures: Tiny Homes (2026)
Tiny home rules in Whatcom County, WA, covering tiny houses on wheels (THOWs), park model RVs, and tiny home on foundation builds, determine where they are legal and how they get permitted.
Key Facts
- Max size
- 400 sq ft, excluding sleeping lofts
- Site-built home
- Treated as a standard house
- THOW siting
- Licensed RV park only
- Max stay
- 180 days per year in an RV park
- Fine
- Up to $1,000 per day, WCC 20.94.030
Summary
Whatcom County recognizes four kinds of tiny home under WCC § 20.97.200: a site-built unit on a permanent foundation, treated exactly like a standard house, and three types of tiny homes on wheels, treated as a mobile home, a park model trailer, or an RV depending on how each is built and used.
A "tiny home" is a dwelling unit that is 400 square feet or less in floor area (excluding sleeping lofts). For the purposes of this code there are four types of tiny homes, as described below. (1) Site-Built Tiny Home. A tiny home built on site on a permanent foundation that meets the minimum requirements of the International Residential Code (IRC), including provisions of Appendix Q, and is reviewed and inspected by Whatcom County. For the purposes of this code it is equivalent to and is permissible under the same rules as any standard single-family dwelling. (2) Tiny Home on Wheels (THOWs). A tiny home on wheels is a portable structure licensed to be transported on the highways by a motor vehicle. For the purposes of this code there are three subcategories or types of tiny homes on wheels.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4963078; v4 updated 2026-06-23; through 06-23-2026).
Full Breakdown
A site-built tiny home, 400 square feet or less excluding sleeping lofts, must meet the International Residential Code including Appendix Q and passes the same Planning and Development Services (PDS) plan review and inspection as any new single-family house, so it can go anywhere zoning allows a house. A manufactured tiny home carrying an L&I or third-party certification tag is treated as a standard mobile home. Tiny homes on wheels (THOWs) are different: a Type 1 THOW, which needs an external utility hookup, follows the same rules as a park model trailer, while a self-contained Type 2 THOW follows RV rules and may use communal utilities.
955, which caps density at 15 spaces per acre with public water and sewer (seven per acre without), requires a two-acre minimum parcel, sets a 10-foot separation between units and any structure, and limits occupancy to 180 days in any one-year period. Utility hookups are mandatory for every space rented to a park model trailer or Type 1 THOW; spaces for self-contained units can rely on communal facilities instead. PDS administers the site-built review; the recreational vehicle park standards are enforced as part of the county's Title 20 zoning code.
Violations & Fines
Setting up a THOW on an ordinary residential lot outside a licensed recreational vehicle park, or living in one past the 180-day cap, is a Title 20 zoning violation. Under WCC § 20.94.030 the county can issue a notice of violation and a civil penalty of up to $1,000 for each day the violation continues. An owner has 20 calendar days to request remission or mitigation of the fine, and 10 calendar days to appeal a final county decision to the hearing examiner under WCC § 20.94.060.
Frequently Asked Questions
Can I put a tiny home on wheels on my own rural lot in Whatcom County?
Does a site-built tiny home need a building permit?
What happens if I live in a THOW outside an approved park?
Sources & Official References
Other rules in Whatcom County
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