For many years, industrial hemp was illegal in the US due to hemp’s association with drug use, despite the fact that it does not contain more than 0.3 percent THC [...] Building residential homes with hempcrete was therefore effectively outlawed until 2018, when the Farm Bill distinguished between hemp and cannabis plants. Then, in September 2022, hemp building materials were added to the model US residential building code, paving the way for legal use in 2024. — Reasons to be Cheerful
The International Residential Code (IRC) accepted a modified appendix in September that some are hopeful could be a catalyst for further adaptation throughout the building industry. Builders for Climate Action spokesman Chris Magwood says its greatest potential lies in commercial construction, though applications within residential design do present inherent challenges owing to drying times, insulation R-Values, and other factors.
"I don't think that hempcrete will ever play a large role in the residential market," Magwood recently explained to Treehugger. "The fact that it is a composite material that uses a lime-based binder means that it is less insulative than other options and more expensive. Somebody has to mix, form, and cure the material, whether that happens on-site or in pre-fab units or blocks. To meet basic minimum code requirements in colder climates requires at least a 12-inch thick wall, and getting to high-performance levels will mean 16 inches or more, so a builder needs more of a material that is already more expensive."
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This is a great example how just a few folks in the design industry can make major impacts nationally through building code development.
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