Tiny home rules in San Mateo County, CA — 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.
Unincorporated San Mateo County permits tiny homes on foundations as ADUs under state law (Gov Code §65852.2). Movable tiny houses (MTH) allowed as JADUs per HCD guidance. Tiny homes on wheels classified as RVs with storage-only use unless on approved site.
San Mateo County permits tiny homes through multiple pathways under California state law. Foundation-built tiny homes qualify as Accessory Dwelling Units under Gov Code §65852.2 and §65852.22 with no local minimum square footage floor beyond ADU rules. ADUs must be permanent, permitted, connected to utilities, and meet California Residential Code Appendix Q (for under 400 sq ft). Detached ADUs allowed by right up to 1,200 sq ft in residential zones with 4-foot side/rear setbacks. Movable Tiny Houses (MTH) on chassis can be approved as ADUs per HCD Memorandum 2021-03 if they meet ANSI A119.5 and are registered/titled. Tiny homes on wheels without MTH certification are classified as RVs or park trailers under CA H&S Code — residential occupancy prohibited except in permitted mobile home parks. Coastal zone properties face additional Coastal Development Permit review. Fire sprinklers may be required depending on access and distance.
Unpermitted dwelling: stop-work order, retroactive permit or removal. Occupancy without certificate: $500-$2,500/day. Unpermitted RV/THOW occupancy: code enforcement, relocation required. Fire and building code failures: no final inspection, no occupancy.
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See how San Mateo County's tiny homes rules stack up against other locations.
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