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IRC Tiny Houses Appendix (Appendix BB in the 2024 IRC)

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IRC Tiny Houses Appendix (Appendix BB in the 2024 IRC)

2024 IRC Appendix BB; 2021 IRC Appendix AQ; 2018 IRC Appendix Q
US
Local
International Code Council (ICC). It is a model code: it has legal force only where a state or local government adopts it.

An optional appendix to the International Residential Code (IRC), the model code many US states and cities use for houses. It gives tiny houses (400 sq ft or less, not counting lofts) rules written for small spaces. It applies only where adopted.

Covers permanent tiny houses (400 sq ft or less, lofts not counted) built under the IRC where a jurisdiction adopts it; does not cover RVs, park model RVs, HUD-Code manufactured homes, zoning, or places that have not adopted it.

Applies to

ADU & Backyard Homes
Modular Homes
Cabins & Off-Grid Homes
Digital Plans

Who checks it

The building department, or state agency, that adopted it reviews plans and inspects. For a tiny house built in a factory, a state factory-built or modular program, or a third party it approves, may inspect at the plant.

When it matters

When you want a small permanent home (400 sq ft or less, lofts not counted) permitted under the residential code, such as a backyard ADU or small cabin on a foundation. Ask early if your city or county adopted this appendix, and which edition.

What this establishes

  • A definition of a tiny house: a dwelling of 400 sq ft or less in floor area, not counting lofts.
  • Rules written for small homes on ceiling height, lofts (size, stairs or ladders, guards) and emergency escape and rescue openings.
  • That the rest of the IRC still applies, except where the appendix says otherwise.

What it does not establish

  • It is not law by itself. It applies only where a state or local government adopts it, and they may change it.
  • It does not decide zoning: whether a tiny house is allowed on your lot, where it can sit, or minimum home size.
  • It is not the standard for RVs or park model RVs. A tiny home on wheels built as an RV follows other standards and local rules.
  • It is not the federal HUD Code for manufactured homes.

How to verify it yourself

  1. Ask your building department which IRC edition it enforces and whether it adopted the tiny houses appendix (Appendix Q, AQ or BB).
  2. Ask the builder, in writing, which code and edition the home is designed to.
  3. Ask the building department about any local changes to the appendix.

Your next step

Ask your local building department whether it has adopted the IRC tiny houses appendix, and which edition, before you choose a design.

Take the next step

United States

The ICC added the tiny houses appendix to the 2018 IRC (ICC Building Safety Journal). ICC lists it as Appendix Q (2018), Appendix AQ (2021) and Appendix BB (2024).

It is optional. ICC says jurisdictions still have to adopt it. Some states let each city or county decide. For example, Montana’s draft 2024 code rules say a certified city, county or town may adopt Appendix BB.

ICC says the IRC and this appendix focus on how the house is used, not on whether it sits on a foundation or wheels (ICC/THIA guide). In practice, many local governments treat tiny homes on wheels as RVs. Dorchester County, SC is one example. Rules vary.

ICC and the Tiny Home Industry Association are developing ICC/THIA Standard 1215, based in part on the 2021 IRC and Appendix AQ.

Confirm with your local planning and building department.

Canada

Questions to ask

No items found.

Confirm requirements for your property

Confirm with your local building and planning department.

Explore property questions

Sources

Edition:

Appendix Q in the 2018 IRC, Appendix AQ in the 2021 IRC, and Appendix BB in the 2024 IRC. Your area may enforce an older edition or local changes, so the letter and rules can differ.

Last reviewed

October 26, 2026