Using locally grown and sourced materials has enabled the environmental educational charity the Green Light Trust to construct a building which actually has a negative carbon footprint, The Foundry development in Lawshall, a village near Bury St Edmunds in Suffolk using hemp, limestone and an existing building has enabled it to tie up 4 million tons of carbon rather than it being given out in to the atmosphere, according to Ralph Carpenter, the project’s architect.

‘Deep green’

“This is a ‘deep green’ building. There are schemes which propose many features claiming to reduce their environmental impact, but they are quietly forgotten as the construction costs rise or don’t perform once the schemes are built,” he says. Environmental features need to be embedded in the construction methods as well as in the operation of the buildings, he adds. The foundry project combines both new and traditional technologies.

This 1,100 sq metre building which is used for the trust’s offices and training spaces, was constructed using a redundant foundry shed on the site which was relocated across the site it owned. It was dismantled and virtually all, 85%, of the materials were used. Not one skip was required. Disposing of materials is not only wasteful, but carting it away also consumes energy, Carpenter points out.
The use of lime, rather than cement, was important in reducing the energy used in the construction process.

“Manufacturing cement uses up large amounts of energy. If carbon taxation is introduced, it will be heavily taxed, making lime cheaper,” he suggests. Lime is used extensively for the mortar, plaster and to protect the timbers. Lime mortar performs rather differently than cement as it takes longer to set and is more flexible. The low thermal conductivity of lime plaster makes it feel warmer than cement plaster.

Hemp

The hemp which was grown locally absorbing carbon dioxide as it grows, was used in the floor, walls and ceilings as insulating material as it has excellent thermal performance and good soundproofing.

Power is provided from a woodchip biomass boiler which eventually will be fed from timber grown on the trust’s forest nearby. Currently, it comes from Suffolk county council’s woodlands. The building has been occupied for six months and it is taking some time to tune the boiler.

Water is heated by locally constructed solar panels mounted on the building’s roof. Rainwater is stored in an underground tank and reused for the toilets. The trust persuaded the Environment Agency that a connection to the mains sewers was not necessary and the sewerage is treated in reedbeds using bark rings.

The building was constructed using local labour with appropriate training schemes being provided.

Efficiency

Organisations need to constantly assess if their buildings could be more environmentally efficient says Nigel Hughes, the director of the centre. We could benefit from a larger rainwater tank and possibly a weather porch. Rotating solar panels could also help to heat the water, he suggested. The hemp insulation could also be thicker. Currently it is only 50 mm. We should add an extra 50-100mm to retain greater heat, he suggested.

This ‘deep green’ approach is now being planned on other larger building projects in rural areas, says Hughes. There are a large number of redundant barns across the countryside which could be sustainably reused, he says.

Existing structures

“Conventional schemes use breeze blocks, but we show that the existing structures can be reused in an environmentally friendly way.”

Approaches need to be varied according to the local materials. “In the Cotswolds different methods would be required,” says Hughes.

A change in the mindset of builders and training is required, he points out.