Pubdate: Sat, 31 Mar 2001 Source: Financial Times (UK) Copyright: The Financial Times Limited 2001 Contact: Website:

Author: Sally Smith


Traditionally Linked In The Public Mind To Cannabis, Hemp In Its Industrial Form Is A Valuable Building Material. Sally Smith Considers Its Surprising Virtues

The rain is relentless and an insidious easterly penetrates every joint. We are standing in Ralph Carpenter's unheated workshop.

Yet neither chill nor damp seeps from the quarry-tiled floor. Our feet are perfectly warm. Touch the bare walls and instead of a moist clamminess there is a comfortable warmth.

"Hemp," says Carpenter, with confident satisfaction. "It's under the floor tiles, it lines the roof, the walls are made of it. It's simply a superb insulator; warm in winter, cool in summer."

An architect practising from Hartest, a Suffolk village south of Bury St Edmunds, for the past 15 years, he has been pioneering the use of hemp as a building material: the core of the stem a replacement for brick and concrete, the fibres as insulation. He has put it into the fabric of a listed medieval building and built an extension to his own house with it.

Now it is being studied by the Building Research Establishment ( BRE ) in a comparative housing project. For Carpenter working with hemp has involved seeking out specialist suppliers, relearning old building techniques and devising new ones, understanding its nature and the materials that are employed with it, and even finding the one brand of cement-mixer capable of getting it to the correct consistency.

He lists hemp's benefits: environmentally friendly ( no toxic by- products and can be fully recycled ); thermally efficient; lower fuel costs; no condensation; absorbs sound; non-flammable.

"Above all it's infinitely renewable because you just grow it. To build our extension took five tonnes and you can crop five tonnes on one hectare in three months. It doesn't need fertiliser. It outgrows weeds and is not prone to pest and disease.

"At the moment at Pounds 550 a square metre, it is between 5 and 10 per cent more expensive than brick; but once the carbon taxes that will have to be paid on conventional building materials clock in, hemp will become more cost-effective," Carpenter says.

For building, the core of the hemp is chopped and treated in a secret petrification process developed in France and mixed on site.

Construction begins with a timber frame of wood of any quality. Uprights are tied in to a brick plinth set in shallow footings. Plywood panels are lightly attached between the uprights to form a mould into which the hemp is tamped.

A day later the panels come off and between is a solid infill, strong enough to hold the timbers firm without bracing. The next lot of panels is attached and the process continues.

The result is so flexible, strong and durable that the footings under the plinth can be shallow, usually 18in deep, half the depth of conventional footings. The trench is lined with sand, stone, brick rubble or any waste building materials. There is no concrete. "We eliminate the need for cement," he explains.

Carpenter's first hemp building, the conversion of a derelict garden shed, was for former Beirut hostage Terry Waite who lives nearby.

The extension to his own house and other small schemes further perfected the processes. Then came the renovation of a wattle and daub building for Bury Town Trust and the discovery that hemp was a more than adequate substitute for traditional daub made with cattle manure.

English Heritage, at first sceptical, was soon convinced as was the specialist who had been collecting her materials from the nearby cattle market. Some panels have been repaired, others entirely replaced, but it is impossible to say which from the texture and appearance.

Hugh Belsey, curator of the Gainsborough Museum in Sudbury, lives there. Initially concerned by wetness in the walls, he says they soon dried out and the ancient structure is warm and dry and not in any way prone to condensation, which can be a problem with renovated old buildings.

"And I have been pleasantly surprised by the heating bills, far lower than I had expected," he says. St Edmundsbury Borough Council, which grant-aided the trust in saving the building, is continuing to develop the use of hemp with Suffolk Housing Society.

A pair of semi-detached houses are being built of hemp alongside another pair, identical in size and design but in conventional brick and block. On the ground floors hemp will also be laid directly over the ground without a membrane and will be used elsewhere for sound and thermal insulation.

Research - monitored by the BRE - will cover financial and environmental costs in construction and in use over a minimum two-year period. By then hemp may have succeeded in winning over the doubters.

Hope for unloved cousin of cannabis

Hemp is in your tea-bags, disposable nappies, jeans and "paper" handkerchieves. Plumbers put it into radiator joints. The oil from the seed is said to be the most nutritious of all oils.

In eastern Europe it is still widely grown for sail-cloth and ropes. But it was banned in the US because of its threat to the paper industry and Britain followed suit.

The convenient argument against it was its narcotic properties, although it has next to none unlike its cousin cannabis. Nonetheless, to grow it today farmers must have a Home Office licence.