Hempsulation

Innovative insulation acts as carbon sinkBiological materials don’t get much more versatile than hemp. Its latest incarnation is as a building material with solid sustainability credentials. Lhoist, the world’s largest producer of lime products, now offers an insulation solution whereby hemp and lime fibres can be sprayed between timber frames to form a fully breathable insulated wall with laudable thermal performance.

Since hemp absorbs CO2 as it grows, this ‘Tradical Hemcrete’ is in effect a permanent carbon sink. It’s a key feature in the award-winning Three Gardens development [right] in Elmswell, Suffolk, used in each of the 29 houses and credited with removing a tonne of CO2 from the atmosphere for every 20m2 of wall. That’s a very positive contrast, when producing the mineral wool typically used for the equivalent area of insulated cavity wall actually emits about two tonnes of CO2.

Research sponsored by the Pilkington Energy Efficiency Trust shows that the hemp-based product has a satisfyingly measly thermal conductivity of 0.26W/m2k; impressively close to that of mineral wool at 0.25W/m2k.

So how does it compare on price? Mike Haynes, product manager at Lhoist, claims that despite relatively small-scale production, the Hemcrete walls at Three Gardens are near parity to the cost of conventional walls. With all new UK homes required to be zero-carbon by 2016, economies of scale could tip the balance in its favour. And Hemcrete, Haynes adds, is “exactly the kind of product developers will need to consider if they are to make zero-carbon buildings a reality”.– Jon Wallace