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Miscanthus: the game-changer in building construction

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  • 3 min read

With the drive towards efficiency and sustainability in building construction, a new type of insulation and structural material could fundamentally change the industry.

Miscanthus – a carbon positive renewable energy crop that’s grown on around 8,000 hectares of UK low grade marginal land, has been identified as having outstanding building credentials.

“Miscanthus bales would more than satisfy building regulations in the UK with regards to their structural capability as building blocks, and their outstanding insulation value,” says Bee Rowan, straw bale building course leader at the Centre for Alternative Technology (CAT), based in Machynlleth, Wales. “In terms of compression requirements, acoustics and ‘heathy internal environment’ stipulations, miscanthus complies. We know we can build load-bearing miscanthus walls using the traditional straw bale building method, and where the surface as a ready key, can directly take internal clay plaster and external render.”

“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.

Miscanthus ‘two-string bales’, typically in inches 13″H x 18″ W x 42″ L (360mmH x 450mmW x just over a meter long) can be used to build houses employing the same technique that’s been used to build wheat straw bale buildings for over a hundred years. There is also scope to use larger Heston sized bales – which are the typical size of most commercial miscanthus bales, in larger, commercial buildings and warehouse spaces that require a permanently ambient temperature.

“The advances in the miscanthus market are vast and we’re working with world leading plant breeding scientists at Aberystwyth University, who are developing seed-based miscanthus hybrids, most of which can make an excellent building bale” says Bee.

One such scientist, Dr Judith Thornton, research development officer for agriculture and environmental sciences at Aberystwyth University, has been working on breeding the crop specifically for a number of end-uses. “Miscanthus is currently grown from rhizome – it’s planted once and harvested every spring for 20 plus years. What we’re doing is taking wild species and crossing them to develop hybrids that can be grown from seed, that suit particular markets, whether that be for biomass, bioplastics, or especially now for the house building market.”

“And we’re working with commercial partners, Terravesta – the miscanthus supply chain experts behind the growth of the miscanthus market in the UK,” says Judith. “From this year’s harvest, Dr Michal Mos, head of science and technology at Terravesta, has baled up enough two-string bales to build a two storey house.

“As a result, we’re looking for an investor in the project who wants to build the first ever miscanthus house or commercial building with these bales – and we would donate the bales to the project, where just the haulage costs are covered,” says Judith.

In a wider context, the future of miscanthus as a building material could hang on a number of possible approaches. “One of which is to develop miscanthus pre-fabricated panels to build housing – meaning that minimal other materials are required. Such a panel would offer top thermal performance, be carbon negative and loadbearing, so dispensing with the need for any structural timber or other frame. Using this technique, we could erect a building in as little time as just a few days,” adds Bee Rowan.