ENVIRONMENT
Hemp houses
Hemp as a building material is an encouraging development when the number of concerning news items about irreversible climate change is on the rise.
by Martin Oliver W
hen we think about climate change, often overlooked is the substantial chunk of
carbon emissions linked to housing construction. New residential dwellings and renovations typically involve the use of materials with a high embodied energy, such as aluminium, steel, and the cement that alone represents about five per cent of global CO2 emissions. Solutions are needed, involving
greater use of more environmentally sound, renewable materials. Even better is to shift the paradigm entirely, and to build in such a way that each new house removes carbon from the atmosphere rather than adding more, helping to reverse climate change. This is technically possible right now.
ONE SOLUTION: HEMP AS A BUILDING MATERIAL Carbon-negative building material options include strawbale, bamboo, and hemp. Of the three, hemp perhaps has the greatest range of benefits. It is waterproof, non-flammable, termite-resistant, a good thermal insulator, and offers superior acoustic insulation. Due to its breathable quality, in cooler climates hemp discourages condensation on inside wall surfaces, inhibiting the development of mould and its associated health problems. After demolition, hemp walls are even biodegradable. Being durable, a hemp house will sequester carbon for as long as it stands, and has an expected lifespan in excess of more conventional construction materials.
72 JULY | AUGUST 2017
While they are growing, hemp stems absorb between 1.3-1.6 times their weight in carbon, and depending on the technique used, this translates into 110-165kg of carbon take-up per cubic metre of hemp wall. Typically combined with lime and water, after construction the lime slowly reacts with the silica-rich hemp, causing it to turn to stone. This petrification process results in further carbon being removed. Although the lime is carbon-positive, the net balance of the mixture is carbon-negative, so long as the hemp is not transported a long distance. While much of the hemp currently used in Australia is grown domestically, some is imported.
THE HISTORY OF HEMP FOR CONSTRUCTION Hemp use for construction goes back a long way, with a hemp masonry material discovered on a bridge in France that dates back to the 6th century. The modern hemp building sector is comparatively young, with the first project completed as recently as 1989. Since then, most hemp constructions have been built in Europe, one recent example being a development of 42 homes, known as The Triangle, in the British town of Swindon. While this project has had some teething problems, these are linked to issues other than the use of hemp. In Australia, low-THC industrial hemp
is permitted to be grown everywhere other than the Northern Territory. Hemp has the advantages of needing little
irrigation water, requiring few fertilisers, avoiding pesticide use, and improving soil structure. It grows to maturity in about three to four months, and two to three crops per year are possible here, depending on the climate. Following a decision in May to legalise human consumption of hemp foods, this extra yield will be shifting the economics of the industry onto a healthier footing. The part of the plant used for construction is the shredded inner woody core (known as hurd or shiv), which is separated from the long outer fibres via an industrial process known as decortication.
HEMP CONSTRUCTION IN AUSTRALIA Among the companies building with hemp is Hemp Homes Australia, based in Margaret River, Western Australia. It focuses on passive solar, custom-designed hemp houses, with the first example having recently been completed, and five others in the pipeline. To secure a local hemp supply, Western Australia’s growers are calling for investment in a processing plant that would allow locally sourced hemp to be used, or better still, for a network of them dotted around the state. Colin Steddy, director of The Hemp Corporation, has plans to invest in getting one off the ground. A couple of Australian ecovillages
under construction will be using hemp. These are Shepherds Ground, near Maitland in the Hunter region, and
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