The other side of the coin: Understanding embodied carbon
Embodied carbon has traditionally been overlooked as a cause of emissions in the built environment. But as the decarbonisation agenda gathers momentum, that could be about to change.
From naturally grown bricks to wooden skyscrapers, biobased materials can change the built environment.
Fabrizio Varriale, World Built Environment Forum
6 September 2021
Besides its significant demand for energy, the built environment is also a large consumer of material resources.
These are mostly minerals (rocks, gravel, and sand), metals, and fossil oils used for plastic manufacturing. In developed economies such as the EU27, the construction sector is the largest single consumer of metals and uses more minerals than all other industrial sectors combined. Indeed, minerals are essential for the modern building: from concrete, to bricks and stones, to glass, plaster and ceramics. But although they are abundant materials, they are not renewable and often require invasive and polluting processes for their extraction.
In the effort to reduce the environmental impact of construction, researchers and designers have turned their attention to biobased alternatives. Biobased materials are organic resources produced by plants and animals, such as timber or sheep’s wool. In the context of construction, biobased materials can have several benefits over conventional ones:
Traditional and vernacular architecture across the world has always made large use of biobased materials available in the local environment. Nomadic peoples often relied on shelters made entirely of biobased materials, such as the Native American tepee or the Mongolian yurt. As humans adopted a more settled and sedentary way of life with the development of cities, architecture came to favour a wider range of minerals. Culturally, we have learned to associate bricks and mortar with stability, safety and prestige.
Traditional and vernacular architecture across the world has always made large use of biobased materials available in the local environment. Nomadic peoples often relied on shelters made entirely of biobased materials.
As the environmental impact of minerals, metals and plastic usage in the industry becomes clear, vernacular architecture can inspire us to re-evaluate the use of biobased materials. “Biobased” does not necessarily mean old-fashioned; building material research is increasingly focused on the development of innovative combinations of traditional materials. For example, lime, industrial hemp shives, cotton fibres and timber studs can be assembled into cladding panels that have comparable performance to their conventional counterparts. Researchers are also developing new materials from non-conventional natural resources. Bioplastics can be produced from a variety of plants and are increasingly favoured by the packaging industry as well as in construction.
With so many examples from nature to be inspired from, the potential for new products appears limitless. Mycelium – the vegetative part of fungi – is a particularly promising material. It only takes five days to grow mycelium boards and bricks in a mould filled with organic waste and infused with fungal spores. The process happens naturally, and the only energy needed is a little heat to stop mycelium growth at the right moment. While mycelium bricks have lower compressive strength than conventional bricks, they are much lighter, and thus ideal for non-structural uses such as insulation and internal partitions.
Timber is probably the most commonly used biobased material in construction projects. Having left behind the typical modernist enthusiasm for concrete and steel, contemporary designers often choose timber for iconic architecture pieces – such as the Metropol Parasol in Seville, Spain. But the use of timber structure does not need to be confined to landmark buildings. Across the world, examples of medium-rise buildings with timber structures are increasing. In Paris, the Office in Wood building provides 17,000 m2 of space over nine storeys. Designed by Baumschlager Eberle and SCAPE, the building rests on a bridge platform spanning over several railway lines. Given the need to limit the load on the bridge, a timber frame, 30% lighter than conventional concrete or steel, was the obvious choice. So far, the tallest timber-framed structure ever built is the Mjøstårnet office in Brumunddal, Norway, designed by Voll Arkitekter. The building uses glued laminated timber to reach 85 meters of height, corresponding to 18 storeys.
Europe's journey towards becoming the world's first carbon-neutral continent is gathering momentum, with the release of the "Fit for 55" package the latest landmark moment. But what is it, and what does it mean for the built and natural environment?
Biobased materials generated by the agriculture sector might compete for productive land against the food and bioenergy sectors. Thus, biobased materials should ideally be natural by-products of other supply chains.
Alongside their multiple environmental and health benefits, biobased materials also have their drawbacks. Fire resistance can be an issue, but there are technical solutions and means of managing the risk. For some materials, such as flax fibres used as insulation, performance is not as standardisable as for heavily-processed materials like polyurethane, which can be an obstacle to production certification. In terms of cost, biobased products can be more expensive than their traditional counterparts, but this is in part due to the lack of economies of scale in their manufacture. To drive prices down, there is a clear need to foster demand and upscale production capacity.
For some materials, upscaling production might mean competing for the necessary natural resources against other supply chains. Materials generated by the agriculture sector might compete for productive land against the food and bioenergy sectors. Thus, biobased materials should ideally be natural by-products of other supply chains – for example, low-grade sheep wool. Alternatively, they can be produced from ‘break crops’ (secondary crops grown as part of the primary crop rotation cycle), such as industrial hemp, or ‘border crops’ (crops grown in-between and at the borders of other crops). Natural resources that are abundant in nature and can be exploited through sustainable practices – wood and algae, for example – are also great sources for biobased materials. In this context, it must be noted that the ‘stuff’ of which these materials are composed, i.e. biomass, has a highly-complex molecular composition. It is much more efficient, and clever, to employ biomass in long-term assets such as buildings. The alternative is to burn it for energy generation – effectively destroying its useful and marvellous complexity for a quick gain. Overall, there is a strong argument for increasing the use of biobased materials to manufacture products, especially for the construction sector. Beside their environmental and health benefits, biobased materials are clearly highly compatible with the circular economy concept. However, biobased materials might never be able to replace metals and minerals in specific uses in construction. A truly sustainable future for the sector must include biobased materials alongside a more efficient and circular use of non-renewable resources through recycling and reuse.