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UK: The green, green grass that's home
David Taylor The Telegraph
Saturday 14 Jun 2003 It's barely legal, but hemp is here to stay - as a low-cost, environmentally friendly building material. David Taylor meets a family putting it to the test Jessee Mulcock has heard them all in the year she has lived in her new house: "You'd have to be dopey to live there." And "Hope your chip pan doesn't go up - the fire engine wouldn't be able to get through all the hippies standing downwind." And "If you run out of booze, you can always smoke some of the wall insulation . . . " Being the butt of such feeble jokes is the price Jessee has to pay for living in a house made almost entirely out of Cannabis sativa - hemp, for short. And, let's face it, that does sound rather like a dope-smoker's equivalent of Hansel and Gretel's gingerbread house. "Yes, we've had a lot of jokes, but at least when people find out what it's about, they stop laughing. They're interested," she says. Jessee, 26, and her six-year-old son, Vincent, are willing guinea pigs in an experiment to test the environmental, technical and economic benefits of using hemp as a building material. Her house, and the one next door, which is also made of hemp, have been built in the Suffolk town of Haverhill for social housing provider Suffolk Housing Society. The idea of using hemp came from the architect, Ralph Carpenter of local firm Modece Architects, who believes that this fast-growing crop could offer a cheap, sustainable and effective alternative to traditional building materials. "I found out about it through my brother Stuart who at the time was working for Hemcore [the UK's largest processor of hemp]. He told me about a hemp-based material which is made in France and used for building," explains Mr Carpenter. The qualities of hemp fibre are well known. It was the first choice for rope before the advent of man-made fibres and it still makes the best quality paper. But the plant's role in the illegal drugs trade suppressed its legitimate use for most of the 20th century, even though commercially grown hemp contains only negligible amounts of the psychoactive drug THC. In recent years, however, pressure from industry has led to a relaxation of the laws governing the cultivation of hemp with the result that it has bounced back and found its way into a range of new products, from clothing and cosmetics to ice-cream. Today, hemp's environmental sustainability is a major selling point. It is easy to grow, even on poor soil, and is ready to harvest in just four months. Like all plants, it absorbs carbon dioxide - the main "greenhouse" gas - from the atmosphere as it grows and, because it requires very little energy to process, it can help save money, conserve fossil fuels and reduce carbon dioxide emissions. The French material used in the construction of Jessee's house is called Isochanvre, a by-product of fibre production consisting of the pith and sap processed to minimise its biodegradability. Mixed with hydraulic lime and water to bind it together, Isochanvre is packed into timber formwork and left to solidify like concrete. It is an easy material to work with and requires fewer skills than building in brick. Its good insulating properties mean that no wall cavity is needed, and its resistance to moisture means that the walls can sit on a ground-floor slab cast in the same hemp-and-lime mixture without the need for a damp-proof membrane. The two hemp houses at Haverhill are built around timber frames with the hemp mixture used as in-fill between the timber beams and columns. The houses form part of a development of 18 properties on the site and are flanked on either side by two similar houses built with traditional materials. These provide a benchmark against which scientists from the Building Research Establishment in Watford can assess the hemp houses. The first hemp house took almost twice as long to build as the equivalent brick houses, mainly because the contractor had to learn how to use the unfamiliar materials from scratch. "But once they got the hang of it, they were very fast," says Ralph Carpenter. "The second hemp house was quicker to build than the conventional brick ones." In terms of its performance, the hemp material seems just as good as brick-and-block construction, according to the BRE's preliminary report to Suffolk Housing Society. Jessee, though oblivious to the science involved, confirms: "It's warm and dry and comfortable, and it has a lovely rustic feel to it, even though it's a new house," she says. One unexpected benefit of the hemp material is its acoustic behaviour. Slightly quieter, according to BRE measurements, than the conventional houses, the hemp/lime mixture seems to deaden sounds within the building. "The acoustic properties have a noticeable calming effect," says Mr Carpenter. As the material is more "breathable" than modern gypsum plaster, the hemp houses also suffer less condensation than their conventional counterparts. Liz Garrod, the BRE's project co-ordinator at Haverhill, is impressed by the hemp houses but confesses herself puzzled by the material itself: "I don't know how they process it, but it looks just like the Hutch Hemp I use for my rabbit's bedding." Laboratory tests bear out the fire- and rot-resistance claims, and Ms Garrod says her own experiments at home with Hutch Hemp have yielded comparable results. Whatever the special properties of Isochanvre, Ms Garrod thinks hemp could have a bright future as a building material. "I like houses made out of natural materials, and this is very sustainable and can be recycled," she says. "It's faster to use than some of the traditional building methods, like cob and rammed earth, which are also becoming popular again." As for Jessee, she has nothing but praise for hemp: "When I moved out of my old first-floor flat on the other side of town, all I wanted was a house. But when I learned about this project, I really wanted to be a part of it.
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