Last reviewed 1 April 2022

Looking towards plant-reinforced building materials may be the next major step in carbon reduction. These materials could offer relief for supply shortages, improve on insulation needs and make significant efforts towards sustainable design. Carbon-conscious construction and development are essential for the UK’s journey to Net Zero. Here, we explore the current picture in the development sector and discuss some bio-composite materials, with their potential.

Taking Stock

Construction has generally been dictated by the natural resources immediately available in a local area for millennia and building design has generally followed material accessibility. Global trade allowed for access to cheap materials but at a cost of a high carbon footprint due to logistics and shipping and, in many industries, severely unsustainable practices such as unmitigated logging. Unfortunately, however, building material availability has been severely strained following trade uncertainty brought on by Brexit, logistical issues following lockdown and now market instability due to the Russian invasion of Ukraine.

Moreover, the construction material disruption is compounded by rising price inflation, which is mainly driven by lack of raw materials, the rocketing price of energy and costs surrounding freight and labour. Following the Ofgem February energy cap announcement, which brought an average bill increase of 54% from April, it is uncertain how energy-intensive sectors such as steel, cement and concrete will react. It is likely, however, that increasing costs will be passed on as higher prices to customers.

With the UK facing growing supply challenges on several fronts and net zero ambitions now putting further pressure on the construction sector, the stage is set for sustainable material science innovation to play its part in sustainable development. By combining modern construction techniques and plant-based materials, which have the potential to be locally sourced, both supply issues and carbon footprint can be mitigated simultaneously.

Green by design

While plant-based materials are by no means a modern invention, such concepts having been present since the advent of human dwellings, by utilising plants with high carbon uptake and absorption, and exploiting the plants’ natural structures, these materials in many cases are cheaper to produce and could be considered as an effective carbon sequestration model depending on the source of the plants and the planned material lifecycle, especially where the material is plastic-free.

Construction materials which are composed of two or more constituent materials where one is naturally derived are called bio-composites. The inclusion of the naturally derived material typically improves properties and performance over those of the individual component materials and specific material properties can be selected from different plant materials, such as strength, stiffness, hardness or even insulating properties.

The construction industry is uniquely carbon rich due to the multifaceted aspects of construction. Using bio-composite materials whose natural components are derived from low cost and low impact agricultural input, with fast growing and high CO2 biomass uptake plants, gives rise to potentially significant reductions in carbon emissions. Additionally, construction waste and material life cycles can be considered where the bio-composite is biodegradable, generating useful by-products such as bio-methane, fostering a circular economy model.

Building for the future

Some commercial bio-composites have already been tested and put to practice in the UK and Europe, and many more are in development. A material known as Hempcrete has been used as wall panels and blocks for a unique sustainable development in Cambridgeshire called Margent Farm. Hempcrete is made up of the woody core of hemp plants (Cannabis sativa) and mixed with lime and water to form the bio-composite. It has also been reportedly used within some houses in the progressive housing development in Graven Hill, Oxfordshire.

Due to the high silica content in the plant’s natural fibres, the hemp binds well to the lime, creating an effective cementitious insulating material that is between one seventh and one eighth lighter than traditional concrete. During the growth of the hemp for the bio-composite, CO2 is taken up by the plant and where lime is cured during the application of the material, further carbon uptake occurs, making the material highly effective at carbon emission reduction.

Unfortunately, the material does not match the compressive strength of standard concrete, or the density, and as such would still require an additional load-bearing frame to support the structure. This negative aspect, however, could be reasonably offset by the huge reduction in cost of production as Hempcrete is relatively cheap to make and ship.

Another bio-composite which holds high potential as an insulation material alternative is the bamboo-based (Phyllostachys edulis) “MycoBamboo”, which has uniquely high carbon storage alongside its naturally flame resistant, thermally stable and significant reinforcement properties, borrowed from the mycelium (fungal root) structure within the material. Due to bamboo’s incredible growth rate, this material offers particularly high carbon uptake, while again being cheap to produce and completely plastic free.

In addition to its construction properties, a recent study showed “MycoBamboo” to have encouraging net global warming potential reduction values once the product’s full life-cycle carbon pathways had been evaluated.

Putting down roots

While these technologies show warming potential for the future of some aspects for sustainable construction, they do not provide an overall answer to the UK’s current construction issues. Both hemp and bamboo can be grown in England, saving on the emission footprint for transport, but design red tape and existing housing incompatibility may just provide a sticking plaster solution, pushing larger complications down the road. These kinds of materials could, however, be the first legitimate steps towards tangible carbon emission reduction for construction in the UK.