There are opportunities for circular design, recycling and re-use at each phase of the building life cycle.

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Transitioning to a circular economy is one of the essential paths towards reducing carbon emissions in buildings. Critically, it requires rethinking how buildings are designed. Design decision-making during each phase of a building’s life cycle offers opportunities to reduce embodied carbon. Informal construction sectors tend to already excel at a circularity and reuse, however in formal sectors, key circular economy design strategies include computer-aided design optimisation for less material usage, selecting materials that reduce non-renewable material extraction, designing for material and component reuse, and extending the life of buildings and/or materials through proper maintenance.

Despite growing awareness, most contemporary material cycles continue to be more linear than circular. As a result, non-renewable,energy-intensive materials still supply the majority of demand. So far, recycled materials are not available in sufficient quantities and qualities,and the gap between supply and demand for recyclables is growing in most sectors. A new supply-and-demand model is needed, with new enterprises that allow for the careful dismantling of buildings and for the storing, preparation and maintenance of second-cycle materials for resale that will enable circular economies while providing job opportunities.

Facilitating access to reliable information and verification is key. Decision-makers must support efforts by stakeholders across the building industry as they seek to decarbonise materials. The current fragmentation of the industry is undermining decarbonisation efforts – with insufficient cooperation among manufacturers, architects, engineers, builders and recyclers. Efforts by individual stakeholders to improve decarbonisation outcomes will not succeed unless they are supported by policy and finance across the different phases of the building process. For example, efforts by designers and communities to use more recycled materials are often stymied by the growing gap between supply and demand. Yet this gap cannot be closed without the adoption of building codes that require designers to specify  “circular” components made with re-usable, renewable materials. Even small improvements to synergistically support both producers and users through policy and finance would be preferable to isolated actions.

Avoid New Extraction by Enabling a Circular Material Economy That Prioritises Re-Use and Recycling

In developed economies, it is critical to improve industry methods across stakeholders, from designers, to communities and to commit to repurposing the massive quantities of failing reinforced concrete from20th-century infrastructure that is nearing the end of its first life, so that it can be transformed into material “banks” for new construction to slow the pace of non-renewable material extraction. To do so, far more investment is required for research and development of design and secondary manufacturing methods with equipment to recover and process construction, renovation and demolition materials.

Government incentives, awareness campaigns, and legal and regulatory frameworks have shown to be effective to incentivise approaches for re-use and recycling. Recycling systems for building materials tend to require similar kinds of support across countries, including promoting markets for re-usable products, providing incentives for the creation of re-use centres and developing specialised contractors. Due to the interdependent nature of the built environment sector, in which many materials may be used across building systems and types, far more investment is required for measures that ensure cooperation across sectors and borders.

Innovating beyond business-as-usual forestry: materials that are truly renewable require regenerative approaches to resource management that incentivize biodiversity.

In pursuing the second pathway to decarbonization, there are transformative opportunities to develop ecologically sound methods for managing the carbon cycle of regional forests and agricultural lands, with important co-benefits to consider, as well as risks. Bio-based materials may represent our best hope for radical decarbonisation through the responsible management of carbon cycles. The shift towards properly managed bio-based materials could lead to compounded emission savings in the sector of up to 40 per cent by 2060 in many regions, even when compared to savings from low-carbon concrete and steel.

However, envisioning and implementing a large-scale transition to circular and bio-based materials in the built environment carries substantial risks if the changes to the broader ecological, social and economic context are not planned for and handled very carefully. Decarbonisation of buildings creates risks of unintended consequences to the ecosystems that underpin the production to supply the alternative bio-based materials. It can also lead to the perpetuation or exacerbation of unjust labour practices, and to inequitable shifts in economic gains and losses as industries transition.

Renewable, bio-based building materials have a unique capacity to drive reductions in atmospheric carbon, if they are sustainably sourced and managed. Currently, wood is the leading scalable biomaterial, and patterns of timber production and use offer both opportunities and challenges. The rising demand for timber could accelerate markets for upcycling by-products from forests and agriculture, adding the massive potential benefits of reducing forest fires and greatly expanding the carbon sequestration potential of both forests and urban areas by up to 70 per cent in certain regions. However, a key prerequisite is that intersectoral approaches to renewable resource and land management are urgently required to transition away from the high carbon impacts of much “business-as-usual” forestry and agriculture.

Key recommendations for bio-based materials include standardisation of performance, integration into building codes, broad industry upskilling, marketing and financial incentivisation, and regulated cooperation in sustainable land-use techniques:

1 — Mandate the Use of Living Systems and Biomass to Protect Urban Climates

Perhaps the most impactful policy for changing the impact of urban materials on climate change is to mandate the use of vegetated surfaces to cover a percentage of exposed concrete or asphalt, wherever possible. This has the combined impact of naturally keeping buildings cool, reducing energy consumption, as well as absorbing storm water to reduce flooding, replenish water tables and urban biodiversity.

2 — Promote the Transition to Low-Carbon Alternative Materials

Decarbonisation of the cement sector and other major emitters is being enhanced by replacing traditional methods with hybrid bio-based materials and other low-carbon substitutes. However, these emerging methods are not yet cost competitive, and widespread biases remain that protect entrenched methods. Thus, scaling up requires substantial investment in research and development of both major and emerging producers, alongside incentives and/or enforceable building codes.

3 — Shift Public Perceptions regarding Traditional Vernacular Materials

Why has it been so difficult to decarbonise building materials, and what can be done about it?  People have not always built with carbon-intensive materials and their future use is not inevitable. Before the middle of the 20th century, the vast majority of cultures built large buildings and cities out of indigenous earthen, stone and bio-based materials – such as timber, cane, thatch and bamboo. However, during the last century, with ever greater access to fossil fuels, the global extraction and production of carbon-intensive, mineral-based materials (such as concrete and steel) exploded and became widely associated with the image of modern progress, strength and expediency.

Yet many contemporary building structures and materials only give the illusion of durability, as they were “designed for obsolescence”. Building assemblies with limited lifespans are now destined for landfills at demolition, as they have been procured through complex supply chains and are not designed for easy disassembly or re-use. An example is the vast number of failing concrete structures with steel and glass façades across the developed world that need to be replaced just a few decades after they were built. Meanwhile, stone, wood and even massive mud buildings have been maintained for centuries with their structures intact.

This report outlines key policies and tools that can be adopted by multiple stakeholders at different phases of the building process that look beyond operational energy and that facilitate the radical acceleration of building decarbonisation, while also bolstering the health of both human populations and biodiverse ecosystems.

4 — Harnessing technology to improve materials while recapturing the intelligence of the past

Contemporary materials do not inherently lack durability. However, it is possible to achieve much better performance from contemporary materials and buildings by harnessing data and technology to revolutionise the means and methods of design and construction. To reach net zero emissions in the built environment sector, the building materials of the future will need to be procured from renewable or reusable sustainable sources wherever possible. If raw material extraction must take place, then dramatically improved methods for decarbonisation must be implemented by transitioning to renewable electrification of all processes, and complemented by carbon capture and storage methods that require substantial support for research and development in order to demonstrate scalability.

TIMBER & WOOD

Future scale up of mass timber and biomass requires careful management of the carbon cycle of forests and agricultural lands in order to increase their net productivity for both carbon sequestration and food and material production.

The built environment uses 38 per cent of the world’s wood products. Increasingly, mass timber is becoming an attractive alternative to carbon-intensive concrete and steel due to its potential for scalability, sustainability, strength and flexibility in mid-rise urban buildings. Advances in timber building material technologies are making it possible to shift towards large-scale structural timber products, provided that the timber industries continue to innovate and are regulated for sustainable practices. Ensuring that the vast majority of timber is sourced from sustainable forestry will be crucial for making this a truly sustainable transition, avoiding pitfalls such as lax regulations, particularly in emerging economies. It is critical to prioritise the development of afforestation practices, particularly in natural forests of tropical countries, where logging rates far outpace effective replanting. “Circular timber” includes the increased use of forest by-products. Both clear-cuts (decaying logs and residues from logging) and off-cuts from wood manufacturing have potential for reconstituted wood products.
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BAMBOO

Scaling fast-growing bamboo shows major promise but requires innovation in carbon-neutral binders.

Bamboo is a fast-growing renewable resource that has witnessed significant advances as a scalable building material in the last two decades. Progress in engineered bamboo has demonstrated structural performance similar to that of cross-laminated timber and steel. However, the variability in species across regions requires investments in further development of low-cost and low-carbon construction methods, standards and certifications to gain the confidence of industry for large-scale applications. As with all engineered bio-based materials, incentives urgently need to prioritise progress in “green chemistry” to develop non-toxic binders and glues. As with timber, the sustainable scaling of the supply of bamboo is critical, with regulations in place that avoid clear-cutting of forests while gaining access to land, and also ensure transparency of sustainable practices throughout the supply chain."
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BIOMASS

The recuperation of by-products from forestry and agriculture has synergistic benefits of reducing forest fires and crop burning.

Non-timber lignocellulosic materials generated from forestry, agriculture and biomass residues represent an untapped but potentially massive local supply chain for building materials, from sources that currently go to waste and contribute substantially to greenhouse gas emissions that also affect air, land and water quality across regions. However, major investments are required. If scaled up to reduce the use of petrochemical and/or timber-based building materials, fast-growing lignocellulosic materials could significantly lower the projected peak in global carbon dioxide emissions.

What is a whole life-cycle approach, and why is it critical for decarbonisation of the sector?

The report emphasises the need to take a whole-life cycle approachwhen assessing strategies to decarbonise emissions from the built environment.A whole life-cycle approach is radically different from a linear approach as it incorporates the principles of a circular economy. It requires consideration of the environmental impacts of material choices before the materials are even extracted, and then again at each phase of the building life cycle, from extraction to processing, installation, use and demolition. This means thinking about how the choice of materials impacts everything from the functioning of regional ecosystems, human health and wellbeing, to the amount of heating or cooling needed – and how, at the end of their use, these materials can provide a “bank”of resources to then be re-used.

When taking such an approach, the work of the geo-biosphere to produce specific local natural resources is valued as a renewable resource. Therefore, the use of bio-based and renewable materials such as timber, bamboo and biomass products must be supported with regulations to protect the ecosystems that sustain those resources, with careful consideration of regionally specific, sustainable land use and forest management. 

Whole life-cycle thinking requires sensitivity to the context – to local cultures and climates. A shift to low carbon earth- and bio-based building materials is often technologically possible but socially difficult to implement, as many cultures consider concrete and steel to be “modern” materials of choice. Yet there is great potential to shift to low-carbon materials due to advances in engineered timber, bamboo and biomass as substitutes for steel and concrete.

1 — Supply of reused and recycled materials will need to catch up with growing demand.

For material producers, some of the highest-priority pathways to decarbonise are by improving the processing of conventional materials such as concrete, steel, aluminium, plastics, glass and bricks. Key to all efforts will be electrifying and decarbonizing the energy that is used to produce and maintain materials, buildings and urban infrastructure across their life cycle. Most material economies continue to be predominantly linear, rather than circular. As a result, virgin and non-renewable materials, that are energy-intensive to produce, still provide the majority of today’s material demand, while recyclables are not available in sufficient quantities and qualities. Reducing raw material extraction and harvesting through recycling and re-use may also mitigate social ills such as forced labour upstream in the supply chain.

2 — Facilitate the Decarbonisation of Conventional Non-Renewable Materials

Cement, steel and aluminium are the three largest sources of embodied carbon in the building sector. The lowest hanging fruit is to facilitate and/or mandate the adoption by industry as well as energy infrastructure planners of already developed best available technologies for decarbonisation, and to maximise the use of clean energy in manufacturing processes.

EARTH-BASED MASONRY

High quality earth-based masonry has potential to replace concrete in many low-rise applications but needs development and regulation.

Diverse earth masonry materials made from clay-rich soil and natural fibres, that are dried in the sun or fired, have been used for much of human history and are often re-used. However, increasingly masonry bricks have adopted the use of high-carbon cement binders and high temperature firing to address mechanical and moisture performance. If locally made with low-carbon binders, additives and processing methods, earth masonry can regain its role as a viable building material for many regions and applications.
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1 — Improve and Increase Access to Reliable, Transparent Data

Common metrics and consistent assessment processes allow decision-makers to accurately weigh the trade-offs among alternative decarbonisation pathways and inform efforts to set standards and trade policy. However, tools to visualise and assess data need to be more accessible, transparent and verifiable to all stakeholders. Whole life-cycle assessments combine embodied carbon with anticipated operational carbon, but the impacts on global ecosystems remain widely under-estimated.

A wider range of tools are emerging to help decision-makers gain easier access to the right data to assess the carbon impacts of their building material choices; however, tools and access to transparent quality data needs to be prioritised, with the burden of including smaller actors shared by formal and developed sectors.

With the right access and training, readily available tools for managing, visualising and communicating the data behind decisions can be game-changing. Tools and frameworks could enable comparison of the pros and cons of different building materials in terms of their embodied, operational and end-of-life climate greenhouse gas emissions. Data management and visualisation tools are emerging that offer “at-a-glance” scenarios to support decision-making in real time.

However, as with environmental assessments and certifications across all sectors, the verifiability and consistency of data remains a huge challenge. The significant range in the quality and quantity of data and certification processes across all material sectors, even the most developed ones, results in uncertainty on the part of material specifiers, especially amongst disadvantaged smaller actors. Moreover, the challenge across all global sectors, from informal to formal construction, is to get the right data to the right stakeholders at the consequential stages of decision-making. For the latter, there is potential to better harness building information models from the design and construction phases, in order to better track the impact of material decisions on the life cycle.

2 — Increase Inclusion and Ensure Fairness in Certification andLabelling Standards

Rising public interest in environmentally sound construction practices has led to a flood of self-declared environmental claims from material producers, with limited traceability – generating scepticism and backlash. International cooperation is required to regulate fair certification, verification and labelling for trade across borders and regions. For true decarbonisation of global material flows, it is necessary to close a “carbon loophole” that disadvantages producers facing strict pollution controls. In turn, it is critical to help smaller producers, especially in emerging economies, to achieve certification, as they are often unfairly penalised with cross-border carbon taxes because they cannot afford, or lack access to, fair certification processes.        

3 — Enforce Performance-Based Building Codes

With the growing adoption of low-cost, digitised tracking methods and access to demand-side metrics such as energy and water use, performance-based building codes have a greater chance to connect to a range of stakeholders across sectors. However, several key impediments still need to be addressed for widespread inclusion of embodied carbon in building codes, alongside the impacts of material choices on global ecosystems and the work of the geo-biosphere.

4 — Empower cities and municipalities as drivers of change to Implement Decarbonisation at the District Level

Governments must improve multilevel governance frameworks and mechanisms to better implement and enforce buildings and construction regulations which support whole lifecycle approaches and low carbon material efficiency strategies. Cities must be empowered to implement and enforce decarbonisation policies in collaboration with national and sub-national government institutions as part of their local action plans for buildings and construction. They need to promote sustainable energy solutions and encourage passive design, circularity, nature-based and neighbourhood level solutions, incentivizing buildings and construction industry stakeholders as change agents. As champions for implementing and enforcing climate policies and targets, cities are uniquely placed to catalyse this transition through their jurisdiction over land use, authority over housing programmes, role in implementing national policies and building codes, and their role in coordinating with local utilities and stakeholders.
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The public sector is often in the best position to implement decarbonisation plans at local or district scale. It can have maximum impact for new development, since strategies for individual buildings can be integrated in synergy with the design of sustainable, electrified grids for the management of energy, water, waste and transport. Policies and ambitious targets from local and national governments establish leading precedents for integrated decarbonisation across multiple scales of infrastructure and buildings. This is only possible if material choices and urban planning avoid driving up cooling demands through the creation of urban heat islands and instead lowers the overall operational carbon of cities by mandating biomass materials and other cool surfaces.

5 — Harness Public Procurement to Support Decarbonisation of Materials

In many countries, the public sector can play a leading role in demonstrating and enabling building material decarbonisation through its procurement powers. However, policy goals for decarbonisation must be formally linked to the purchasing of materials planning phases with rigorous whole life-cycle assessments to serve as examples for effective solutions across specific local climate types and building traditions.

6 — Tackle Gender Bias in Both Formal and Informal Building Sectors

Gender bias is prevalent across the different phases of the built environment process. In many formal sectors, the two principal issues to act on are: 1) closing the large gender pay gaps that persist across the architecture, engineering and construction industries, and 2) addressing the overwhelming dominance of men in senior decision-making and administrative roles. Across informal sectors, the urgent priorities should be: 1) enforcing national and municipal regulations for safety and improved working conditions at construction sites, and 2) promoting skill development among casual labour to enable the transition to fairer and more consistent labour conditions. 3) In the shift towards bio-based materials, critical attention should be placed on protecting ecosystems and workers from toxicity and environmental degradation from unsound agricultural and forestry practices.

In conclusion, the built environment sector must learn to design with nature-based processes if it is to decarbonize. This means reducing the burdens on the geobiosphere from “extracted”, toxic, non-renewable materials, and increasing regenerative, renewable and circular materials. However, all material sectors need to be included and policies can create synergistic opportunities for both conventional and emerging industries. For example, decarbonisation of the cement sector and other major emitters can be enhanced by shifting to bio-based binders and other low-carbon replacements.

However, many of these emerging decarbonization methods are often not yet cost competitive, and widespread biases remain that protect entrenched methods. Sustainably scaling up implementation cannot be enforced without substantial investment in research and development alongside incentives and/or enforceable building codes. Although the shift from extracting to growing building materials presents major opportunities, there are substantial dangers of an unregulated shift towards biomaterials backfiring and causing unmitigated environmental degradation.

Thus, international cooperation is critical. Policies can be synergistic with improving strategies to decarbonise the embodied energy of materials within the formal sectors across the globe, as these are the sectors that are consuming and producing the majority of carbon emissions in the built environment today. At the international climate level, action is required for countries to address embodied carbon in their Nationally Determined Contributions (NDCs) towards reducing emissions under the Paris Agreement, and the next steps towards ensuring firm commitments need to be legislated through enforceable building energy codes. Despite the massive contribution to global emissions from embodied carbon within building materials, it has previously been under-addressed in strategies to reduce building emissions. Thus, the responsibility for galvanising a future net zero economy for the built environment sector should be spread across producers and consumers within the formal global building sector, both public and private, in order to bolster the transition to a clean, just, renewable, circular building materials economy.