International Residential Code Appendix Q. Setting the standard 

Building high quality homes is important no matter the size of the home. The International Code Council publishes the International Residential Code (IRC) which is the Gold standard for building modern stick built homes. And while the IRC is comprehensive, it does not meet the intent and purpose most have for building a Tiny Home on Foundation. Enter, Appendix Q. Appendix Q used in conjunction with the IRC follows the existing standards with exceptions related to size being addressed in the Appendix. Tiny Homes on Wheels (THOW) generally are built to an RV standard. These must comply with National Fire Protection Association standards for RVs.

According  to Appendix Q, What is officially a Tiny Home 

If you look at Tiny Homes on foundations designed as permanent housing, they are usually anywhere from 350 to 600 square feet. This small foot print allows for all the comforts of home on a small scale. IRC Appendix Q recognizes any dwelling that provides living, sleeping, eating, cooking, and sanitation facilities under 400 sq. ft. as a tiny home .  One of the size  concessions related to Tiny Homes is ceiling height. Appendix Q allows ceiling heights as low as 6 feet 8 inches in habitable spaces. Many modern new construction Tiny Homes opt for cathedral ceiling styles to add visual square footage which makes the space feel larger and more open. While lofts and elevated sleeping areas can offer additional habitable area, they limit the flexibility and marketability to only those able to navigate to the sleeping area. They may create a barrier to those with mobility limitations.  Other building requirements generally follow the  IRC.