Welsh team build world’s first house from miscanthus

Image: CAT/Paul Williams

The first house to be built from miscanthus bales is taking shape in Wales.

A collaborative project by the University of Aberystwyth, the Centre for Alternative Technology (CAT) and commercial partner Terravesta is exploring the potential to use the miscanthus crop as a building material as a way of helping decarbonise the construction industry.

A perennial carbon-negative renewable energy crop that is grown on around 8,000 hectares of low-grade marginal UK land, miscanthus has been identified as having outstanding building credentials, with excellent insulation value.

Following successful test building last year, the partners are now working on building a miscanthus bale house that will still be standing in 100 years.

The miscanthus bales are being used as infill 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, said: “The most ground-breaking thing about 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% 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.”

Straw bale building expert Bee Rowan (left) and homeowner Steph Robinson install the bales

The build uses “two-string bales” supplied by Terravesta, an expert in the miscanthus supply chain.

These are just over a metre long, 45cm wide and 35cm high, making them a convenient building block size that can be handled easily.

There is also scope to use larger Heston-sized bales – which are the typical size of most commercial miscanthus bales – in larger buildings and warehouse spaces.

World-leading plant breeding scientists at the Beacon Project at Aberystwyth University’s IBERS (Institute of Biological, Environmental and Rural Sciences) are developing seed-based miscanthus hybrids that work well in straw bale building.

Dr Judith Thornton of the Beacon Project said: “Miscanthus is currently grown from rhizome – it’s planted once and harvested every spring for 20 plus years. 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 – whilst building directly with bales is ideal for self build housing, in the future we could also be using prefabricated panels of miscanthus to build houses, and we could produce loft insulation or fibreboards.”

The bales are being incorporated into the Little Welsh House Project being run as a series of short courses by the Centre for Alternative Technology, helping self-builders get to grips with environmentally sound building materials and methods.