Figure 2.6.1 Scope 1, 2, and 3 carbon accounting for a material product
Figure 2.6.2 Carbon impacts of materials across the whole building life cycle
Taking a “whole life-cycle” approach means considering all the carbon costs of material choices.
The built environment process involves energy, material and information flows at each of its life-cycle phases, from initial material extraction to final dismantling. The typical approach to the design and construction of buildings is linear, where at each phase of the life-cycle, the embodied carbon of a building accumulates. This increase in embodied carbon results from the use of energy and materials to: 1) source and extract building materials, 2) manufacture the materials, 3) construct the building structure from the materials, and 4) maintain the building during its service life. Hence, with each life-cycle phase there typically is a carbon investment.
Increasingly, however, industry leaders are promoting a fundamental shift towards a circular, “whole life-cycle” approach to guide strategies to reduce both the embodied and operational carbon associated with building materials. (See tools in chapter 6.) A whole life-cycle approach is very different from a linear approach. It requires stakeholders to cooperate towards consideration of the environmental impacts of material choices before the materials are even extracted, and then at each subsequent phase of the building life cycle. This means thinking about not just how buildings are constructed, but also how the choice of materials affects 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 for another building’s life cycle.
Looking at the building process from a whole life-cycle point of view means considering all the carbon costs of material choices, from the impact of material extraction on ecosystems to the environmental effects of production, construction, maintenance and demolition (see Figure 2.6). “Whole life-cycle emissions” are a combined measure of the embodied emissions in building materials and the operational emissions from a building’s energy use and energy-source emissions (Magwood et al. 2021). By making assessments and decisions about carbon impacts over the course of the entire building life cycle, we can allow for choices that optimise for carbon efficiency between both embodied and operational carbon.
The whole life-cycle approach supports the deployment of a circular economy by enabling cooperation across stakeholders. If a new building’s materials can be sourced from recycled materials at the beginning of its life – or, conversely, if a building’s materials can be recycled at the end of its life – this will mitigate its embodied emissions and thus its total emissions over its lifespan. The main strategies for decarbonisation across a building’s life cycle – from design to operations to end-of-use – must inter-relate for prime optimisation. The key to achieving whole life-cycle thinking is to ensure that the right decisions are made early in the design process to determine the carbon impact over a building’s lifespan and end-of-life (see chapter 3). This is true not only at the building scale but also at the district level: material choices in urban design affect the wider ecosystems with which a building will interface (from land and water quality to the electric grid), as well as their relative impacts.
Whole life-cycle thinking requires being sensitive to the context, including local cultures and climates. Although a substantial shift to low-carbon building materials – such as recycled and earth- and bio-based materials – is technologically possible, it may be socially hard to implement, as many regions consider concrete and steel to be the “modern” materials of choice. Such a shift has tremendous potential due to growing experience with engineered timber and bamboo as substitutes for steel and concrete, and the ability to use components derived from forestry, agriculture and biomass by-products. Yet none of these improvements can scale impactfully without innovation and whole life-cycle coordination across producers, designers, builders and communities.