To mitigate dangerous ongoing climate change, it is critical to move aggressively to decarbonise the built environment sector. Across regions, methods will vary in implementing the three main decarbonisation principles outlined in this report: 1) Avoiding non-renewable extraction, 2) Shifting to bio-based sustainable materials, and 3) Improving conventional building materials and processes.

Material flow scenarios for developed versus developing countries highlight key differences. In developed countries, the focus should be on incentivizing the renovation of existing and ageing building stock to transition to high-performance buildings. In developing countries, rapid urbanisation underscores the need to set and then enforce performance-based building energy codes for new construction, starting with the public sector to set the standard. In emerging economies, policies that focus on the decarbonisation of the built environment sector must also address the needs of the informal and semi-formal construction sectors, where the bulk of the labour force resides.

Reducing embodied carbon in building materials to net zero is achievable by 2050, if we promote the use of best available technologies for conventional materials, combined with a major push to advance the upcycling of biomaterials from forest and agriculture streams. The greatest potential to decarbonise the sector lies with the ability to manage carbon cycles by removing mature trees and decaying forest and crop residues, in order to store the carbon within building materials and products. This would produce compounding benefits, from reducing the risk of forest fires, to increasing the productivity of forested land tracks through rejuvenation and responsible reforestation – thereby increasing the carbon uptake from forests while reducing climate change emissions from the burning of crop waste.

The increased use of properly managed bio-based materials could lead to 40 per cent emission savings in the built environment sector by 2050 in many regions, even as the transition to low-carbon concrete and steel occurs in parallel. Increased demand for decarbonised bio-based materials could increase the carbon uptake of responsibly managed forests in some regions by up to 70 per cent by 2050, compared to baseline scenarios. Supporting the use of all best available technologies will greatly bolster the effort, but substantial research and development is still required to deploy more sustainable methods for bio-based materials. This is especially true in the area of green chemistry for binders, glues and treatments that enable forestry and agricultural by-products to be engineered into structural systems.

Reducing the extraction of non-renewable materials is further bolstered by the development of circular design for re-use and recycling, alongside the electrification of all processes with  renewable energy and the development of at-plant carbon capture and storage to increase material strength by up to 30 per cent in sectors such as cement. Reducing material use through data-driven design optimisation to support the transition to sustainable materials and systems that are derived from renewable bio-based sources such as timber, bamboo and agricultural biomass will require more complex information management and communication across stakeholders. Policies need to support the development of accessible analytical tools, but they also need to mandate their use through building codes.

In pursuing these strategies, there are important co-benefits to consider, as well as risks. In particular, envisioning and implementing a large-scale transition to circular, 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.

The report emphasises the need to take a whole-life cycle approach when assessing strategies to decarbonise emissions from the built environment. When taking such an approach, the work of the geo-biosphere to produce specific local natural resources is valued. 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.

In order to galvanise the market and to enable designers, building owners, and communities to make the right decisions, tools to support the decarbonisation of building materials require more rapid progress. These tools must be supported by access to better quality data and transparent audits conducted by qualified third-party reviewers. More synergy could be leveraged in combining the certification of fair labour and environmental practices / working conditions. In the informal sectors, stakeholders typically have neither the access to data nor the means to conduct analyses or certification, thus greatly disadvantaging both producers and builders in emerging economies from decarbonizing their output, for both local and export markets.

Thus, international cooperation is critical to support fair certification and labelling. Such 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. 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.