Figure 3.2 Opportunities to reduce carbon in each stage of project development
The potential to avoid embodied carbon is greatest during the planning and design phases.
Source: HM Treasury 2013; World Green Building Council 2019.
Upstream Design Choices Are Key to Tackling Carbon Early
Early design choices have repercussions on the ability to reuse or recycle materials later on.
The potential to reduce and avoid embodied carbon is greatest during the early planning and design phases (see Figure 3.2) (HM Treasury 2013; World Green Building Council 2019; PEEB 2021a). At this early planning stage, taking a whole life-cycle approach to project future low-carbon scenarios is key. Circular design strategies focus on how upstream design choices impact embodied carbon throughout the life cycle. Early design choices have repercussions on the ability to reuse or recycle materials later on.
Designing Out Waste and Emissions from the Start
The first question to ask is whether anything new needs to be built at all.
A circular economy approach aims to design out waste. The priority is to keep materials and buildings in use as long as possible and to ensure that they are re-used rather than turned to waste. Many opportunities exist in both new construction and renovation to design out waste, avoid embodied carbon and plan ahead by incorporating strategies earlier in the life cycle.
The first question to ask is whether anything new needs to be built at all. Alternatives to new construction should be explored. For existing buildings, circular renovation and retrofit strategies, such as extending the life of the building, coupled with advanced recovery and recycling, are key to achieving low-carbon outcomes. Where new construction is a necessity, designs should aim to maximise building lifespans and to promote resource and material efficiency, thereby reducing the embodied carbon expended. During this early phase, embodied carbon emissions can be avoided by eliminating new materials, such as by increasing the use of existing assets and promoting adaptive re-use.
Importantly, upstream design choices have repercussions for potential end-of-life strategies. These include choices about building morphology, material selection, and construction assemblies (which affect both embodied and operational emissions) as well as the potential for disassembly at end-of-life. Considering the end-of-life during these early phases can result in the avoidance of waste and associated carbon emissions later in the building life.
This underscores the importance of using evidence-based decision-making in the selection of materials, with regard to embodied emissions, in this phase. One key way to promote evidence-based design is by enacting performance-based building standards and undertaking regulatory reforms to allow for performance-based rather than prescriptive standards, to enable the use of alternative low-carbon materials and construction techniques. (See chapter 6 for more on tools.)
Circularity Strategies Are Context Specific
On the path towards decarbonisation, different decisions will need to be made depending on whether there is a need for new construction, or for renovating existing buildings. New construction and renovation are happening globally (UNEP and IEA 2017). However, if the current linear approach to renovation and new building construction continues, it will exacerbate climate change.
Decarbonisation strategies will differ by region because of variations in the available building stock. Material flow scenarios suggest that in developed countries, the priority is to renovate existing and ageing building stock and to repurpose waste into material “banks.” In developing countries, rapid urbanisation means a focus on new construction; in this context, designing out waste in the early stages is promising. However, in both contexts, designing buildings that are easily reused, repaired or recycled at their end-of-life is vital if we are to shift from a linear to a circular economy.
