Biomass

Non-timber lignocellulosic material streams generated from forestry, agriculture and biomass residue streams represent key local building material solutions. Globally, models of the annual biomass supply outweighs projected construction demand. If scaled up to substitute or reduce the use of petrochemical and timber-based building materials, fast-growing lignocellulosic materials can lower the projected peak in CO2 emissions, shifting it by 50 years. However, such materials today represent a small market share of building materials and rely on expensive and complex processing techniques. Both “push” and “pull” market approaches are needed to scale up and ensure widespread adoption of bio-based building materials. Policies that financially incentivise the capture and value addition of biomass building materials need to be coupled with marketing and education programmes.

Supplies of Biomass Residues Outweigh Current and Projected Construction Demand

Building materials from forestry, agriculture and biomass residues are key local solutions.

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.

Adapted from Keena et al. 2022.

Biomass-Based Construction Can Result in Lower Carbon Emissions

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.

Living biomass systems canreduce operational carbon emissions in buildings.

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).

Figure 4.6 Examples of green building envelopes usingliving biomass and other climate-friendly features

Living systems haveshown promise in reducing heating and cooling loads and the urban heat islandeffect.

Source: Arup 2016

Figure 4.7 Relationship between embodied and operational carbon within living biomass material systems

Trade-offs exist between theembodied costs of assembling the systems and their ability to offset or storecarbon.

Source: Ciardullo and Dyson 2023

Box 4.3

The benefits of integrating living biomass systems in buildings

Many municipalities globally have recognised the benefits of integrating vegetated surfaces or living materials (plantings, soils, and structures that support them) as a solution to reduce urban carbon emissions (Liberalesso et al. 2020). Such living biomass material systems – including green roofs, façades and indoor wall assemblies (see Figure 4.6) – can offer ecosystem services that have been displaced by urban hardscaping (Manso et al. 2021; Shafique et al. 2018)
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Compared with conventional materials, living biomass material systems provide comparable or improved energy savings from insulating and cooling effects (Shafique et al. 2020; Bevilacqua 2021; Theodosiou 2009)). Some living wall systems contribute up to 58.9 per cent energy savings compared with exposed concrete wall systems, particularly in high-sun areas (Coma et al. 2017). In addition, such systems have consistently been shown to reduce the urban heat island effect (Santamouris 2014; Shishegar 2014) and to offset the carbon costs of urban stormwater infrastructure (Berndtsson 2010; Wang, Eckelman and Zimmerman 2013).
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In indoor applications, living systems can improve air quality and reduce the energy costs of mechanical ventilation (Feng and Hewage 2014; Torpy, Zavattaro and Irga 2017; Mankiewicz et al. 2022). The ability for exterior systems to actively participate in ongoing carbon sequestration is still under investigation (Whittinghill et al. 2014). One study concluded that converting all exposed concrete building roof areas in the U.S. city of Detroit to low-profile green roofs would have the same carbon savings as removing 10,000 sport utility vehicles from the road (Getter et al. 2009).
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Each living biomass system is highly dependent on design-specific elements, including the type of structure used, the choice of plant species and growing media (see Figure 4.7). Design choices reveal an integrated relationship between embodied and operational carbon (Ciardullo et al. 2022; Mankiewicz et al. 2022, Kosareo and Ries 2007, Koroxenidis and Theodosiou 2021; Rowe et al. 2022; Susca 2019). For example, systems that require additional materials for irrigation systems or for sub-structures that carry the weight of soil and water can have higher embodied carbon (Ottele et al. 2011). However, this relatively small increase in material might be offset by operational carbon savings, as additional soil thickness and water-holding capacity has more impact on reducing heating and cooling loads (Raji, Tenpierik and van den Dobbelsteen 2015, Rowe 2011).
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The embodied costs of biomass systems might be offset in the future through the use of recycled, renewable and lightweight material substrates (Rincon et al. 2014; Chenani, Lehvävirta and Häkkinen 2015; Tams, Nehls and Calheiros 2022), organic fertilisers (Chafer et al. 2021) and system designs that reduce water use (Natarajan et al. 2015). Because many benefits of living biomass material systems manifest at the urban scale, municipalities should expand incentives for these systems to help offset initial and ongoing maintenance costs.

Straw bale Insulation Has Proven Carbon Benefits

Straw biomass offers a low-carbon opportunity to replace petrochemical-based insulation.

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.
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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.

Carbon Benefits of Myco-Based Biomass Still Need to Be Demonstrated at Scale

Myco-based materials harness fungi’s capacity to transform biomass into building products.

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.

Key Steps FOR

Scaling Biomass as a Sustainable BuildingMaterial

Improve management of the biomass supply chain

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

Encourage biomass use in buildings, rather than for short-lived energy and industrial applications

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.

Create incentives to encourage the conversion of biomass into building materials

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.

Reducethe potentially high embodied carbon associated with biomass-based materials

Coordination and research must be improved along the supply chain to avoid increased carbon emissions from biomass collection, treatment and mechanical processing.

Promote just labour practices in biomass industries

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).