Bath team tests properties of hemp as building material

A consortium, led by the BRE Centre for Innovative Construction Materials based at the university, has constructed a small building out of hemp-lime to test its properties as a building material.

Called the ’HemPod’, the one-storey building has highly insulating walls made from the chopped woody core, or shiv, of the industrial hemp plant mixed with a lime-based binder.

The hemp shiv traps air in the walls, and the hemp itself is porous, providing a good level of insulation. The lime-based binder sticks together and protects the hemp and makes the building material fire resistant.

The industrial hemp plant takes in CO₂ as it grows, and the lime render absorbs even more of the climate change gas, effectively giving the building an extremely low-carbon footprint.

Dr Mike Lawrence, research officer from the university’s Department of Architecture and Civil Engineering, said: ’While there are already some houses in the UK built using hemp and lime, the HemPod will be the first hemp-lime building to be constructed purely for scientific testing.

’We will be closely monitoring the house for 18 months using temperature and humidity sensors buried in the walls, measuring how quickly heat and water vapour travel through them.’

Lawrence said that, since the walls are breathable, the internal humidity is kept constant and the quality of the air within the house is very good. As the pore structure of hemp shiv combines with the properties of the lime binder, the building is also thermally efficient and the temperature in it stays fairly constant.

Prof Pete Walker, director of the BRE Centre for Innovative Construction Materials, added: ’The aim of the project is to provide some data to persuade the mainstream building industry to use this building material more widely.

’Hemp grows really quickly; it only takes the area the size of a rugby pitch to grow enough hemp in three months to build a typical three-bedroom house.

’Using renewable crops to build houses can also provide economic benefits to rural areas by opening up new agricultural markets. Farmers can grow hemp during the summer as a crop between their main food crops – it doesn’t need much water and can be grown organically.

’Every part of the plant can be used, so there’s no waste – the shiv is used for building, the fibres can make car panels, clothing or paper and the seeds can be used for food or oil. So it’s a very efficient, renewable material.’

Environmentally friendly building materials are often more expensive than traditional materials, but the Renewable House project funded by the Department of Energy and Climate Change (DECC) and the National Non-Food Crops Centre (NNFCC) cost around £75,000 (excluding foundations) to build a three-bedroom Code 4 house from hemp-lime, making it competitive with conventional bricks and mortar.

The project is sponsored by the Department for Environment, Food & Rural Affairs (Defra) under the Renewable Materials LINK Programme. Project team members include BRE, Feilden Clegg Bradley Studios, Hanson UK, Hemp Technology, Lhoist Group, Lime Technology, the NNFCC and Wates Living Space.