Non-timber lignocellulosic materials generated from forestry, agriculture and biomass residue streams represent key local building material solutions. Current models of bamboo and straw, two fast-growing renewable biomass resources, show that annual supply outweighs demand (Göswein et al. 2022). Each year, an estimated 140 gigatons of by-product biomass is generated worldwide (Tripathi et al. 2019). Current end-of-life pathways for biomass, such as landfills and incineration for energy recovery, miss out on the true opportunity for value addition and carbon storage in long-life building materials (Langholtz, Stokes and Eaton 2016; Lan, Zhang and Yao 2022).
Figure 4.5 Comparison of life-cycle carbon dioxideemissions per square metre for four wall assembly types
Wall systems made fromcross-laminated timber, bamboo and coconut-biomass residues show emissionsavings.
While cross-laminated timber assemblies are advocated as the key load-bearing alternatives to concrete and steel, such approaches overlook the inability of the current timber supply to meet projected demand. In general, when compared with traditional wood frame construction, wall systems made from cross-laminated timber, bamboo and coconut-biomass agricultural residues demonstrate much lower CO2 emissions and environmental impacts on a life-cycle basis (Keena et al. 2022) (see Figure 4.5). Across these bio-based material assemblies, design-for-disassembly strategies, which enable component re-use, have been shown to result in 10-50 per cent CO2 emission reductions (Keena et al. 2022).
If scaled up to substitute or reduce the use of petrochemical and timber-based building materials, fast-growing lignocellulosic biomass can lower the projected global peak in CO2 emissions, shifting it by 50 years (ibid.). However, coordination must be improved along the supply chain to avoid increased emissions from biomass collection, treatment and mechanical processing. Biomass feedstocks can be of poor or non-standardised quality, and their availability can be highly distributed or erratic.
In addition to biomass-based materials, the integration of living biomass systems – such as green roofs, façades and indoor wall assemblies – in buildings can bring decarbonisation benefits by reducing heating and cooling loads, while also having the potential to improve air quality (see Box 4.3).
Straw biomass offers a critical opportunity to replace high-carbon petrochemical-based insulation. Straw is the widely available leftover stalk harvested from a diverse range of fast-growing cereal plants, such as wheat, maize, rice and other grains. Compared with conventional insulation materials – including polystyrene, mineral wood, cellulose fibres and rock wool – straw bale insulation demonstrates much lower CO2 emissions (Koh and Kraniotis 2020), with the market opportunity for bio-based insulation growing.
When integrated into walls, straw has demonstrated the ability to reduce operational carbon. Load-bearing straw bale houses have been found to have a carbon footprint of between 20 and 1,000 kilograms of CO2 per square metre, compared to more than 600 kilograms of CO2 per square metre for conventional construction (Bocco 2014; Bocco Guarneri 2020; Koh and Kraniotis 2020). This wide carbon footprint range highlights the importance of design for effective integration.
Another promising bio-based option that has emerged over the last two decades is the use of mycelium, the vegetative state of fungi. Myco-based building materials are gaining attention due to fungi’s capacity to bind a wide range of cellulosic components of agricultural, forestry and food biomass waste streams into chitin-bound building insulation, fibreboard, particle board and bio-brick products. However, more research is needed on the scalability of methods and the carbon footprint of these materials.
Due to the requirements for high-quality biomass, myco-production entails high levels of refrigeration and drying, requiring the use of plastic moulds and sterilisation. Myceliumenterprises are often unable to obtain sufficient supplies of high-quality, consistent, single-stream biomass and may turn to importing high-quality feedstocks, further driving up emissions.
Overall, advancements have been made in developing material requirements as well as production and construction standards for biomass-based building materials. However, to accelerate their uptake in both retrofits and new construction, financial incentives are needed to promote development of methods alongside circular, biodiverse design approaches.
Provide opportunities for Commercialisation of bio-based materials is largely led by small and medium bio-based enterprises and start-ups in order to, which must compete with well-established reconstituted wood and petrochemical insulation industries (Langholtz, Stokesand Eaton 2016).
Integrate approaches to land use, residue management, and the creation of eco-manufacturing firms in order to lower the costs of biomass collection, increase availability, and improve quality control and product standardisation
It is important to incentivise industry to use biomass for longer-life applications, as short-lived applications, such as fuel or paper products, drives up emissions.
Policy support is needed to encourage the conversion of biomass feedstock to materials such as bio-based insulation, bio-aggregate products, and alternatives to timber and wood products.
Both “push” and “pull” market approaches are required to scale up adoption.
Policies that financially incentivise intersectoral collaboration need to be coupled with consumer campaigns and technical training for architecture, engineering and construction stakeholders.
Coordination and research must be improved along the supply chain to avoid increased carbon emissions from biomass collection, treatment and mechanical processing.
A critical lever for biomass industries in the near term is to ensure qualitative gains across the whole life cycle, including ensuring healthy and just labour conditions and environments (Heerwagen 2000; Loftness et al. 2007).