What changes when you build a tiny house yourself instead of buying one finished?

Published September 28, 2026

Summary

Mostly the rulebook. A finished unit from a factory may be sold as a HUD-code manufactured home, as a recreational vehicle, or as neither, and federal rules define an RV as built for recreational use, not as a primary residence. A tiny house you build on your own land falls under your state and local residential code instead, and some states, Oregon among them, have a separate code for homes of 400 square feet or less.

Three categories, three sets of rules

	HUD manufactured home	Recreational vehicle	Small site-built house (Oregon)
What defines it	8 body feet or more wide or 40 body feet or more long in travel mode, or 320 sq ft or more when set up, built on a permanent chassis as a dwelling	Not certified as a manufactured home; designed only for recreational use, not as a primary residence or for permanent occupancy	Detached one-family dwelling of 400 sq ft or less
Rule it's built to	HUD construction and safety standards (24 CFR 3280)	NFPA 1192 or ANSI A119.5	Oregon's Small Home Specialty Code, based on the 2018 IRC including its tiny house appendix
What you'll see	A metal HUD tag outside and a data plate inside	For park models, a manufacturer's notice given before the sale	A local building permit and inspections

A unit smaller than HUD's size thresholds can still be a manufactured home if its maker voluntarily certifies it to the HUD standards. HUD also published a proposed rule on June 12, 2026, to revise the definition, so the thresholds above could change.

The park model notice

For park model RVs built to ANSI A119.5, the manufacturer has to give the buyer a notice before the sale that says the unit is designed only for recreational use and not for use as a primary residence or for permanent occupancy. If you're buying a tiny house to live in full time, that notice describes a different use from the one you have in mind.

Building one on your own lot in Oregon

Oregon law (ORS 455.616) says dwellings of 400 square feet or less must comply with the Small Home Specialty Code, which adopts the 2018 International Residential Code, Appendix Q included. The state's 2023 residential code adds its own sleeping loft rules: the loft floor has to be under 70 square feet, the ceiling above the loft floor at least 3 feet high, and the clear height below the loft at least 7 feet. In a house this small, those numbers shape the floor plan. Other states may not have adopted any tiny house provisions at all, so the local building department is where that answer comes from.

If you're buying a finished unit, find the labels

HUD's rules call for a roughly 2-by-4-inch aluminum label on each transportable section, mounted at the taillight end, around 12 inches above the floor and 12 inches from the road side. Inside, a data plate near the main electrical panel, or in a kitchen cabinet or bedroom closet, shows on a map which wind zone and snow load the home was built for. HUD doesn't reissue a missing certification label, which matters if you're looking at a used unit.