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Hemp-Lime Appendix Published in 2024 US Model Residential Housing Codes

The International Code Council's update of the International Residential Code for 2024 included Appendix BL Hemp Lime (Hempcrete) Construction. The successful submission of hemp lime into US residential building codes was a multiyear project of the US Hemp Building Foundation. The USHBF, under leadership of former USHBA Executive Director Jacob Waddell, submitted an application for certification after raising more than $50,000 and working countless hours with a committee of experts, including civil engineers, hemp-lime builders from Europe and the USA, architects and code experts who helped straw bale builders become certified in the 2018 residential housing codes.

"The forward-thinking visionary/pioneers who went before to establish this code are owed a deep gratitude," said said Ray Kaderli, USHBA president. "This gratitude will be best expressed by our unified professional focus and efforts to educate and execute with excellence."

"We have done something that they said could not be done!" said Waddell (now founder of the Hemp Building Institute) on social media.

Volunteers and experts who helped with the ICC submission included US and international hemp builders Cameron McIntosh, Matt Marino, Martin Hammer, Chris Magwood, Graham Durrant, Henry Gage, Jr., Tim Callahan, Gary Fox, Mattie Mead, Jennifer Martin, Tom Rossmassler, Anthony Néron, Laurent Goudet, Sergiy Kovalenkov and Dion Lefebvre. Architects included Kiko Thébaud, Anastasiya Konopitskaya and Bob Escher. Consultants Martin Hammer,Anthony Dente and David Eisenberg  and administrator Mary Dempsey also assisted with the project, among others.

Hempcrete, a mixture of hemp stalk hurds or “shiv” and lime binder, creates a long-lasting fibrous insulation wall assembly that is fire-resistant, carbon-sequestering and repels mold and pests. Because hemp sequesters carbon in the walls of a building, hempcrete is an excellent zero-carbon building material that can offset the construction industry’s carbon footprint.

Hempcrete insulation has been used in Europe for about 30 years, but wasn’t officially included in US building codes because industrial hemp was illegal in the United States until passage of the 2018 Farm Bill.

With more hemp homes being built in the United States, hempcrete is becoming more familiar to local building officials.

What's in the Code? 

Appendix BL will allow use of hemp-lime in buildings up to two stories in regions of low seismic risk prescriptively without engineering. Regions of high risk and taller buildings still fall under the code, but will require an engineered design.

The IRC is a model code for one- and two-family dwellings and townhouses, and is the basis for the residential code in 48 states (except Wisconsin and Arkansas), said Martin Hammer, a natural building architect and one of the consultants hired by USHBF to help draft the code. The appendices are optional and must be adopted by a state or local jurisdiction to be enforceable, Hammer said. Many states do not adopt many IRC appendices, he said. Most states are in the middle of their 3-year cycle adoption of the 2024 IRC.

"If Appendix BL is not adopted by a state or local jurisdiction (including now) or if a project falls outside the IRC's scope (e.g., commercial, institutional, multi-unit residential) Appendix BL can be proposed for use on a project basis to the local building official," Hammer added.

Long-time Canadian natural builder Chris Magwood, manager of the Embodied Carbon division at RMI expressed cautious optimism on social media:

"Given that many states aren't even yet using this new code, let alone adopting its appendices, this is no guarantee that a given hempcrete project will be able to go forward using this," Magwood wrote.

"However, what I've found - even in Canada - is that the existence of code language to support a material like hempcrete can be a big help in convincing code officials that even if they aren't using this code and this appendix there is a basis for them to take a hempcrete application seriously and code language to use to assess the application."

USHBA recognizes that hemp building materials are an answer to the construction industry's desire for regenerative, biogenic natural materials that can help curb the industry's carbon footprint. The association's goal is to make hemp building materials a go-to solution for the US construction industry, said president Kaderli.

"My long-standing approach his been to be on a 'Pathway to Production,'" Kaderli said in an email.  "The scale of the crop can be overwhelming in all of the opportunities created as it makes it’s way alongside corn, soy, wheat, cotton… To capitalize on the scale of this opportunity the building space must keep a steady focus on the end goal of production building and home remodeling," he added.

"Custom homes and demonstration projects have started the process. Now supporting codes can make broader adoption possible," Kaderli wrote. "Great things lie ahead."


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