The use of hemp as a raw material in building is gathering currency within sustainable circles, especially as green regulations are fast coming on stream, writes Oonagh Reidy.

Hemp’s properties help in the drive to reduce carbon emission due to its natural carbon minimizing features. As is grows, it helps limit environmental pollution as it actually decomposes CO2 within itself.

This versatile material is used for a variety of general purposes including paper, health food supplements, fabric and since 1996 the cultivation of low-narcotic hemp has been permitted again in parts of Europe. The method of growing is also highly eco friendly, improving the soil in which it grows and because hemp matures to a height of 4m within 100-120 days, weeds are unable to grow so no herbicides or pesticides are necessary during cultivation.

A considerable number of construction materials can also be sourced from hemp fiber, including composite fiber board which is said to be both lighter and stronger than comparable wood products, 2x4's, lightweight concrete substitutes that have both insulative and soundproofing qualities. As a natural insulation product which can be available in either roll or mat form it is 100% pollutant-free, ruling out any risk to health either in production or installation.

Isochanvre, a French based company has already built over 250 hemp homes and are said to have used Hemp fiber with lime to create a thermal and acoustical barrier, which is far stronger than when using concrete products.

BRE conducted a study several years ago into the use of hemp to construct houses in by a housing association in Suffolk and found it to be a highly suitable material for eco friendly homes, although cost was a factor finding it far more costly than conventional brick homes. However, the report experts are sure the costs will fall.
The project involved the construction of eighteen dwellings, 16 of which were built using conventional construction methods and materials but two of which involved Hemp.

BRE studied the two systems for its relative structural, thermal, acoustic, permeability and durability qualities, costs, reduction in waste on site, and its environmental impact and overall costs.

The research made the following findings in relation to the hemp throughout the building of the houses:

Structure & durability: The qualities of hemp homes were found to be at least equal to
those of traditional construction.
Thermal comparisons: Heating fuel consumed by the hemp homes is no greater than
that used in the traditionally constructed houses.
Acoustics test: Hemp homes did not perform as well as the traditional houses but they
did meet the sound resistance requirement.
Permeability: Both forms of construction appear to give complete protection against water
Construction costs: It is estimated that the true cost of hemp construction was £526 per
square metre compared to £478 for traditional construction. r penetration. However, the hemp homes generate less condensation.
Waste minimisation: There appears to be little difference in the amount of waste produced by each method. Although the waste is of a different nature in each case both are likely to have an environmental impact.

The differences between the two forms of construction were also examined in terms of its sustainability, the economic and environmental differences.

The BRE report’s principal concluded that hemp homes have far less impact on the environment in terms of their energy to build, wastage and take less fuel to heat, but cost about 10% more to build than brick and block houses. It was found that the cost per square was £526, compared to £478 for traditional construction (around €750).

However, it added that is expected that this cost will go down with production efficiencies and economies of scale. In addition, they found that the material conducted more noise than block and brick, although it still met sound resistance regulations.

More recently, another housing development also in the UK used Tradical Hemcrete, which is a mix of hemp and lime, as a spray on its walls. This material is made of shiv, which is the material from the core of hemp plants and pure lime, and it can be sprayed onto a timber frame, much like concrete, or cast between temporary shuttering to form a wall panel.

However, it appears the use of hemp is still very rare and some issues have still to be tackled, for instance one one insurer Zurich, will insure buildings made from the material.

TO View the full BRE report on Hemp:.
http://projects.bre.co.uk/hemphomes/HempHousesatHaverhillfinal.pdf