Source: dailycommercialnews.com
Builders working with industrial hemp would like to get one fact out of the way — while the material is a member of the cannabis family, it contains only a negligible trace of tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana. When that same hemp is combined with lime and water it forms hempcrete, the cornerstone of traditional hemp construction and an excellent insulator.
Hemp Technologies with head office in Winnipeg is one of the companies promoting the use of hemp as a food, biofuel and building material. Stew Oliver is a consultant to Hemp Technologies and one of the owners of The Enrix Group, an Orillia-based builder specializing in residential and small commercial construction, sustainable energy projects — and hemp building.
"While the name hempcrete sometimes inspires images of concrete blocks containing hemp, the process of building with hemp goes back far before modern concrete," says Oliver.
"It's a generic building product that might more correctly be called hemp lime."
Builders use hemp hurd, a product extracted from the pithy core of the plant, and mix it with lime using vertical shaft or pan mixers. It's poured into forms that sandwich a load-bearing stud wall and then slip-formed to any height. Conduits can also be inserted into the forms to accommodate wiring and plumbing.
"The material doesn't slump, demonstrates more flexibility than concrete and cures within a few hours," says Oliver.
"While it doesn't have notable load-bearing capacity, it weighs only one-seventh the weight of concrete by volume and helps to strengthen the stud wall. It's also fire retardant and resistant to termites, mice and other varmints."
Oliver estimates that a hempcrete wall eight to 12 inches thick can produce an insulating value of R-20 to R-30, depending on the mix.
"It also offers significant thermal mass," he says. "It holds onto heat in the winter and helps a building to remain cool in the summer."
Hempcrete is permeable to the atmosphere, allowing it to breathe and maintain indoor air quality through the curtain wall.
"You can eliminate the vapour barrier and all of the engineering required to accommodate it," he says. "You can go with the natural finish of the material inside, or you can finish the wall with magnesium oxide board, which is also permeable."
Traditional hemp building is being rediscovered in many European countries with some of the heaviest adoption in France. European buildings constructed with hempcrete have stood as long as 800 years.
"In Europe we're now seeing not only residential but commercial hempcrete building projects," says Oliver. "In England builders have used precast hempcrete panels to build Marks & Spencer department stores and breweries."
Residential hemp construction projects are permissible under Section 9 of the Ontario Building Code as alternative solutions. Oliver built his own home using hempcrete and is working on plans for other residential projects, including several contracts involving First Nations housing.
He's currently working with organizations such as CSA to have the product certified so it can be specified on commercial projects.
Canada eased restrictions on growing hemp more than a decade ago, while the U.S. is slowly following suit. Plants can be harvested at about two metres tall for food crops, but can be grown as tall as five metres for industrial applications.
"Canada is a North American leader in producing industrial hemp, with the greatest production in Alberta and Manitoba," says Oliver. "We're also seeing some interest in hemp as a cash crop in Ontario. Right now we're getting most of our hemp from Manitoba with some from Europe until we develop an established domestic supply line."
The up-front costs of building with hempcrete are slightly higher than building with concrete, but Oliver says costs are difficult to compare until more widespread adoption of hemp building sets a Canadian market price for construction-grade hemp.
"We're not going solve the world's problems with hempcrete," he says. "But with certification, and the right training for builders, we believe we can provide the construction industry with a renewable, energy-efficient product that offers a lot of benefits."
Photo
Hempcrete is permeable to the atmosphere, allowing it to breathe, maintaining indoor air quality through the curtain wall. It can eliminate the need for a vapour barrier.Photo: Stew Oliver
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