What is IRC Appendix Q (now AQ) for tiny houses?

It is an optional appendix to the International Residential Code for dwellings of 400 square feet or less, not counting lofts. It first appeared as Appendix Q in the 2018 IRC and is labeled Appendix AQ in the 2021 edition. It relaxes some rules that are hard to meet in very small homes, mainly ceiling heights, lofts, loft stairs and ladders, and emergency escape from lofts. It is not law unless a state or local government votes to adopt it, and adoption differs from place to place. The 2018 version did not cover tiny houses on trailer chassis. Ask your building department whether it has adopted the appendix.

Check your local rule. This varies by state, county or city. Your permitting office has the final word; the official lookup pages below show you who that is.

Sources

• The International Residential Code has a big vision for tiny housesInternational Code Council
• 2021 Seattle Residential Code Appendix AQ: Tiny HousesCity of Seattle SDCI