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Little did we know when campaigning for the Fingal energy standard in 2005-06 that Construct Ireland would have a direct impact on Ikea’s first Irish store. Driven by a combination of Fingal’s requirements and their own renewable energy policy, the Swedish retail giant has invested in the largest ground source heat pump installation in Ireland and the UK, along with a well-thought biomass system fed by an onsite waste stream and a host of other green measures, as John Hearne reports
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No matter how energy efficient a building method is, constructing a
house from scratch will always cause some damage to the environment -
but what if a building material could absorb more carbon than it causes
to be released over its life cycle? Lenny Antonelli visits a hempcrete house in Co. Down that seeks to trial this innovative method of building
If someone said you could build a sturdy, energy efficient home with hemp and lime, you might call them mad. But as more architects and builders demand materials with both a low carbon footprint and high energy performance, hemp-lime construction – also called hempcrete – is growing. It's hardly a surprise that when it came to building a house for his father, professor of architecture Tom Woolley – one of the UK's authorities on green building – plumped for hempcrete.
"The idea was to trial it," says Woolley, who built the house with his partner Rachel Bevan, also an architect. "As architects we wouldn't specify it for clients without having done it ourselves." The couple built the bungalow beside their own home in a rural corner of Co. Down. They hope to entice Woolley's father from his coastal home in Anglsey, north Wales, to live closer to the pair.
Woolley and Bevan built the walls by mixing hemp shivs – the woody core of the plant – with a pre-formulated proprietary lime binder, then adding water to create a sticky crumble. Lime Technology supplied the radical hemp and lime system for the mix – two bags of lime for each bag of hemp. "Recently they've reckoned you could probably use about one and a half bags of lime to one bag of hemp," Woolley says.
The roof features grass roofing to the rear and a sloping slate finish to the front. The slate roof is designed to be "polite" to nearby vernacular bungalows
The mix was dropped into timber shuttering that was attached to an FSC-certified softwood timber frame. The builders then pressed down the mix, taking care to avoid over-compressing it and forcing air out, which would reduce the hempcrete's ability to insulate. The shutters were removed after 24 hours and the hempcrete was left to dry – because the house was built over winter this took two to three months, but much quicker drying times are possible in summer. Lime render was then applied over the hempcrete both inside and out.
Once dry, hempcrete makes an impressive insulator – tests at the UK's National Physical Laboratory indicate a U-value of 0.23 W/m2K for Woolley and Bevan's 300mm build. While this figure isn't ground-breaking, Woolley says the thermal performance of hempcrete can't be measured by U-value alone. The thermal mass of the material - its ability to absorb, store and release heat - means it can naturally balance out temperature fluctuations and maintain a comfortable indoor temperature. A study by the BRE also found that hempcrete performs better than its calculated U-value.
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