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CAT building to use hemp walls

Posted: 03/03/2008

Walls built with hemp will be a major feature of a new building at the Centre for Alternative Technology (CAT). The innovative mixture of hemp stalks, lime and a small quantity of cement (known as ‘hemcrete’) produces less carbon emissions than conventional concrete, because the cement contained in concrete is fired at high temperatures, using a lot of energy.

The walls are part of the new Wales Institute for Sustainable Education (WISE). CAT is building the £6.2million training and conference venue to extend its courses in sustainable technologies, including courses in solar power for electricians right up to masters courses in sustainable architecture.

Builders are spraying the hemcrete material onto heraklith (or woodwool) boards attached to the inside of the timber frame. The walls on the WISE building will be 500mm thick, providing a high degree of insulation and air tightness whilst remaining breathable. The walls will be finished inside and out with a lime render.

The building includes 24 twin hotel-style rooms, classrooms, workshops, a laboratory, offices, lecture rooms, an extended restaurant and a bar.

These all incorporate other carbon-saving materials and technologies, for example, the circular 200-seat lecture theatre will have 7.2m high rammed earth walls, making them the highest walls of this kind in Britain.

CAT always minimises cement in its building projects – the energy needed to manufacture cement is responsible for approximately 10% of carbon emissions globally. In 2000, CAT’s Information Centre was built completely without using any cement. Many of the foundations in the new WISE building have been laid using limecrete instead of concrete.

It also incorporates a large timber frame, sourced from sustainable forests, which uses less energy to produce than a conventional steel structure.

“We now have more than 400 masters students studying architecture at CAT,” WISE Project Officer Phil Horton said. “The new building will be an inspiring place for them to study, embodying all the principles taught within it.”

WISE is already the subject of a study - PhD student Ranyl Rhydwen is studying the use of hemcrete in the new building.

“All the heating and electricity in the WISE building will come from a range of renewable sources,” Horton said. “This includes a combined heat and power plant burning woodchips, solar panels for electricity and hot water, hydroelectric turbines and several wind turbines.”

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