Hemp can be used in buildings in a variety of ways. Hemp shiv is usually mixed with lime - which acts as a binding agent and preservative - in varying proportions depending on its application. Once hardened, it forms a lightweight, durable, waterproof material that's an excellent insulator.
Floor hempcrete - about 50 per cent hemp and 50 per cent lime - is used to create ground floor paving slabs, providing good thermal insulation, particularly when combined with a screed for underfloor heating systems.
Wall hempcrete, which can be used to construct solid walls in timber-framed buildings, can also be used as an external render.
Lightweight hempcrete, which is about 10 per cent lime to 90 per cent hemp, is good for using as insulation in areas such as between floors, between roof rafters or in loft spaces.
Hemp plaster - a mix of 85 to 90 per cent lime and only small quantities of hemp - is used as an internal plaster finish, which can be left exposed or painted.
Hemp is also becoming invaluable as an alternative to cob, in renovating old buildings. Cob is traditionally made from hardened mud and straw, and is notoriously prone to damp, but a hemp-based substitute is damp-resistant, cheaper than cob, and takes less time to make.
Mixed with other fibres - usually polyester for binding and often waste cotton - hemp makes an excellent insulator for walls, suspended floors, roofs and lofts. It is available either as rigid or semi-rigid boards, or as a quilt-like material, and is easy to cut, fit and install. Due to its high density, it won't slump, even on a sloping roof.
There are at present very few hemp houses in the UK, possibly due to cost. A Building Research Establishment report concluded that while hemp homes have far less impact on the environment than conventional brick ones, they cost about 10 per cent more to build.
However, with the emphasis very much on sustainable building, it looks likely that hemp will increasingly be used in construction and renovation.
Useful links
www.ecomerchant.co.uk
Natural Building Technologies
Contact www.architect-yourhome.com
Visit www.hemplime.org.uk
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