Weed for hempcrete?
The most sustainable building material isn’t concrete or steel — it’s fast-growing hemp. Hemp structures date to Roman times. A hemp mortar bridge was constructed back in the 6th century, when France was still Gaul.
Now a wave of builders and botanists are working to renew this market. Mixing hemp’s woody fibres with lime produces a natural, light concrete that retains thermal mass and is highly insulating. No pests, no mould, good acoustics, low humidity, no pesticide. It grows from seed to harvest in about four months.
The first modern hemp house was constructed in 2010, in North Carolina. There are now about 50 such homes in the USA. But not much hemp is grown in the USA, a little less than 10,000 acres so far, enough for about 5,000 single-family homes. Cultivated acreage in Canada is double that, and in China’s Yunnan province, 10,000 farmers grow it. Roughly 30 nations now produce hemp, including Spain, Austria, Russia and Australia.
Hemp was rediscovered in the 1980s across Europe, where cultivation is legal, and France has become the European Union’s largest hemp producer. Hundreds of buildings across the continent use the substance as insulation to fill walls and roofs, and under floors in wood-framed buildings.
Manufacturers say it’s ideal for low-rise construction, a product that’s stucco-like in appearance and toxin-free. Its promoters also boast that it has a lower carbon footprint, requiring three times less heat to create than standard limestone concrete.
More like drywall than concrete, hempcrete can’t be used for a foundation or structure; it’s an insulation that needs to breathe, said Joy Beckerman, a hemp law specialist and vice president of the Hemp Industries Association, a trade group.
There still aren’t international standards for building with hemp, or codes regulating how it should be used structurally or safely. ASTM International, a technical standards organization, formed a committee to address this in 2017. Nonetheless, the use of hempcrete is spreading. A Washington State company is retrofitting homes with it. Left Hand Hemp in Denver completed the first permitted structure in Colorado last year.
Down south, New Zealanders turned 500 bales of Dutch hemp into a property that fetched around $650,000. In Britain, HAB Housing built five homes with hempcrete last year. Canada’s JustBioFiber recently completed a house on Vancouver Island with an interlocking internal framed hemp-block inspired by Legos.
It’s a niche but growing sector of the cannabis market. In 2015, the Hemp Industries Association estimated the retail market at US$573 million in the United States.
Source: The New York Times Company
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