Figure 5.1 Shares of total greenhouse gas emissions by source, material class and industrial sector
Cement dominates the emissions impact of construction, followed by steel.
Within the construction sector, cement and concrete, as well as iron and steel, play a dominant role (see Figure 5.1). In addition to their emission impacts, many of the most common building materials are not-renewable, meaning that raw material supplies are finite and cannot be replenished. Conventional non-renewable materials – cement/concrete, steel, aluminium, petroleum-based plastics and glass – will continue to comprise the majority of building materials for decades to come, and cannot always be replaced with renewable alternatives.
Given their ubiquity and rising demand, it is critical to decarbonise the major conventional building materials and process, pursuing parallel but very different pathways. Additionally, promising avenues exist to scale up the use of “transitional” building materials, specifically earth-based masonry products, which are non-renewable but typically have lower emissions. These include adobe blocks, compressed earth blocks, fired bricks, and typha clay composites, which can serve as potential substitutes for high-carbon cement-based blocks if certifications and standards are developed and enforced.
In addition to their emission impacts, many of the supply chains for conventional building materials are at high risk for unethical working conditions. The materials with the highest risk of being made with forced labour are rubber, glass, fibre and textiles, steel, electronics, bricks, timber, stone, copper, iron and minerals. As conventional materials are increasingly decarbonised, it is essential that fair labour considerations are coupled with environmental policy targets. (To support decision-making on these combined socio-economic impacts, see the Design for Freedom Toolkit, Grace Farms Foundation 2022.)
Key to all efforts will be electrifying and decarbonizing the energy that is used to produce and maintain buildings and materials across their life cycle. In addition, regions can avoid the extraction of resources by shifting from unsustainable mining of materials towards integration of renewable components and methods. Reducing raw material extraction and harvesting can also mitigate many social ills such as forced labour issues upstream in the supply chain. To advance the circularity of conventional building materials, the supply of recycled content will need to catch up with the growing demand for materials.