Everything you need to know about IRC Appendix Q model building code for tiny houses.
“As advocates, one of our first building code tasks was to get the IRC to recognize the unique product of foundation-based housing under 400 SF. To that end, our organizations and members helped write and approved Appendix Q in the 2018 IRC.
We recently updated that in the newly approved 2021 IRC code Appendix Q. We continue to lobby the 50 states to include Appendix Q in their building code updates—and are pleased to report that the effort has been quite successful.”
-THIA President Dan Fitzpatrick
The International Residential Code (IRC) is a model building code developed by the International Code Council (ICC). As a comprehensive, stand-alone residential building code, it establishes minimum regulations for one-and two-family dwellings using prescriptive provisions for building, plumbing, mechanical, fuel, gas, energy, and electrical. The IRC is in use or adopted in 49 US states, the District of Columbia, Guam, Puerto Rico and the U.S. Virgin Islands.
Importantly, as a model code, the IRC is intended to be adopted in accordance with the laws and procedures of a governmental jurisdiction. During the adoption process, some jurisdictions amend the code to reflect local practices and laws.
Each state adopts IRC codes differently. While some adopt the code in its entirety, others pick and choose the parts they like and use them to augment their state code. Of note, some states have statewide adoption process while others manage the adoptions at the local city or county level.
Regardless of how IRC codes are adopted in your state, a code appendix is NOT automatically adopted along with the rest of the code. Some states offer statewide adoptions, others offer local adoptions, and sometimes it is a mix of the two.
In an nutshell, Appendix Q is a model building code for foundation-based tiny houses, providing building safety standards for houses that are 400 square feet and under.
It relaxes various requirement in the main body of the IRC. Specifically, the Appendix Q addresses the issues related to safety and maximizing efficient design of tiny house. Attention is specifically given to features such as compact stairs, including handrails and headroom, ladders, reduced ceiling heights in lofts and guard and emergency escape and rescue opening requirements of lofts. Read the entire Appendix Q for tiny houses here.
Importantly, it is up to each state and/or municipality to adopt Appendix Q into its residential building code.
When adopted, it provides a pathway for tiny homes to allowed as primary residences or accessory dwellings units through local zoning. Jurisdictions that see there are ICC-approved codes to build tiny homes can be more open to adopt those types of dwellings into their zoning ordinances.
In a huge number of cities, counties, and US states! Browse our Tiny House Resource Map to see which states and jurisdictions have adopted the Appendix Q.
“Jurisdictions may use Appendix Q as a model code to adopt, reference, or amend. Builders or even jurisdictions that have not adopted the 2018 IRC or the Appendix, can seek approval ”on a project basis through the alternative materials and designs provision” in the IRC.”
-David Eisenberg, Appendix Q proponent and Development Center for Appropriate Technology founder
Appendix Q primarily relates to foundation-based tiny homes. However, there are multiple pathways for applying to movable tiny houses on the local level.
One option is to build a movable tiny house off-site to the Appendix Q standards, transport to a residential property and then permitted as a permanent dwelling by placing it on a foundation system. For instance, the chassis could be removed and the house set on piers.
"Tiny house Appendix Q does take away the vast majority of the challenges a moveable tiny house would face, leaving the chassis/trailer as the last major potential roadblock (fear not, there’s good news to follow). As such, builders and owner builders alike can submit an application for the foundation design through Section R104.11 of the IRC entitled Alternative materials, design and methods of construction and equipment. This application simply needs to show how the chassis/trailer can be incorporated into a suitable foundation to meet the intent of the code.
This design could likely draw heavily on Appendix E: Manufactured Housing Used As Dwellings, as the majority of that appendix focuses on mounting a chassis/trailer to a code approved foundation for manufactured housing. This is a great place to start for using the code itself to support your design and long term plans." -Andrew Morrison, Appendix co-author
Lake Dallas Tiny Home Village (LDTHV) is the first example of the Appendix Q being adopted locally for a specific use, within this planned unit development, and amended to allow for moveable tiny houses. All MTHs in the community must comply with this building code (minus the chassis), be tied down, and utilize fire-resistant skirting. Permits are issued after third-party inspection to ensure it meets the Appendix Q, or reasonably meets the intent of the code. Learn more about LDTHV here.
Appendix Q was co-authored by educator, builder, and tiny house dweller, Andrew Morrison, and architect Martin Hammer in 2016. They rallied a team of advocates together for an incredibly organized effort to present at the International Code Council (ICC) hearings and led an advocacy campaign to get it adopted across many states.
Watch the documentary, Living Tiny Legally Part 2 to see history in the making!
The relaunching of THIA in 2019 coincided with the code cycle changes all across the country. THIA took this as an opportunity to help further the work of Martin Hammer, architect and the original co-author of the IRC Appendix Q, to develop relations with code officials and actively participate in the new edition of Appendix Q for the IRC 2021.
THIA helped finance this work and was directly involved with the editing and public comment process, with THIA CEO Brad Wiseman's leadership. Additionally, we have been involved in the public comment stages in numerous states and local jurisdictions to support the adoption of the current version of Appendix Q.
Watch documentary "Living Tiny Legally: Part 2" to see history-in-the-making!
"Becoming a THIA member helped me bring tiny houses to my town. Now, I can live where I want and how I want, legally."
-Jessica B. San Jose, CA
"We entered the Tiny House on Wheels industry because we felt that this product is both of vital future importance, and also that the industry would benefit
from experienced professional construction and standards. THIA stands for exactly these things which are the reason we started building tiny homes in the first
With THIA I feel confident that we are moving towards a fair and correct set of national standards, and as this is an organization that has a real purpose, not just a name and a sticker, we will be a member moving forward. It's also fantastic to have somewhere to get some feedback or secure a referral."
- Jerry Terry, Decathlon Construction