Miscanthus bales could decarbonise construction

A house in West Wales has been built using carbon negative Miscanthus bales in a project aiming to evaluate the benefits and viability of using the plant in construction

Miscanthus bale house in west Wales under construction

This house constructed in West Wales is believed to be a world first as its walls are being made from Miscanthus bales. The house is a collaborative project by the Centre for Alternative Technology (CAT), Aberystwyth University and commercial partner Terravesta to see if the use of Miscanthus as a building material can help to decarbonise the construction industry. 

Miscanthus is a perennial carbon-negative renewable energy crop grown on around 8,000 hectares of low-grade marginal land in the UK. It's been identified as having outstanding building credentials and excellent insulation value and following a successful test building last year, the partners are building a Miscanthus bale house that will still be standing in 100 years.

The bales are being used as in-fill for a timber frame in the same way as wheat straw bales are often used, with the surface of the bales providing a ready key for internal clay plaster and external render.

Bee Rowan, straw bale building course leader at CAT, says the most ground-breaking aspect of Miscanthus is that it could decarbonise the construction industry at scale: 'In conventional building, the carbon footprint is heavy and one house can emit 50 tonnes of CO2. In contrast, approximately 40 per cent of Miscanthus biomass is made up of carbon directly captured from the atmosphere in photosynthesis. Locking this carbon up in building materials actually reduces atmospheric levels of CO2.'

This build uses ‘two-string bales’ supplied by Terravesta, experts in the Miscanthus supply chain. These are just over 1m long, 45cm wide and 35cm high, making them a convenient building block size that can be handled easily. There's also scope to use larger sized bales in bigger buildings and warehouse spaces.

Dr Judith Thornton, a plant breeding scientist at the Beacon Project at Aberystwyth University’s IBERS (Institute of Biological, Environmental and Rural Sciences) is, with her team, developing seed-based Miscanthus hybrids that work well in straw bale building.

'Miscanthus is currently grown from rhizome – it’s planted once and harvested every spring for 20 plus years,' she says. 'Our scientists have taken different types of Miscanthus and crossed them to develop hybrids that can be grown from seed to suit particular markets.

'These have typically been the biomass and bioplastics markets, but by matching up our understanding of the plant properties with the requirements of the building industry, we can potentially breed for the house building market.

'We’ve been using plants as building materials for thousands of years. What is different now is that we understand enough about the physical and chemical properties of plants and have more processing techniques available to us. This opens up a lot of opportunities – while building directly with bales is ideal for self-build housing, in the future we could also be using pre-fabricated panels of Miscanthus to build houses at volume, and we could produce loft insulation or fibreboards.'