The carbon associated with a building’s lifecycle come from two main sources – ‘operational carbon’ and ‘embodied carbon’. Operational carbon refers to emissions that arise from providing heating, cooling, water and power. There is a direct link between design choices and operational carbon performance. For example, using insulation, efficient building services and renewable energy generation will result in proportionately lower operational CO2 emissions.
Embodied carbon is the carbon dioxide emissions associated with creating a building. This includes emissions caused by extraction, manufacturer, transportation, assembly, maintenance, replacement, deconstruction, disposal and end-of-life aspects of the materials and systems that constitute a building.
As buildings become increasingly energy efficient, they use less energy and rely on low & zero carbon (LZC) heat and power sources. However, the proportion of a building’s lifecycle carbon that comes from the embodied carbon becomes more significant.
The most widely used method for assessing embodied carbon is life cycle assessment (LCA). This is a systematic procedure for compiling and examining inputs and outputs of materials and energy, and the environmental impacts directly attributable to a building and its materials throughout its life cycle.
LCA results for products or materials are presented in the form of environmental product declarations (EPDs). These can be used to compare the performance of different materials, as they certify the carbon and environmental impact of products. EPDs are therefore an important and reliable information source for conducting building LCAs.
The objective of LCA is to optimise the efficient use of resources and to minimise the environmental impacts of the building during construction and throughout its life. This is fundamental to a whole life carbon assessment as understanding what will happen to a building in-use is essential to the successful design of low embodied carbon buildings. LCAs will allow more informed decisions to be taken in terms of reducing carbon emissions and also in relation to other aspects of performance, such as material, water and energy use across the whole lifecycle.
LCA relies on robust raw data and tools, such as EPDs, as well as expertise to interpret the results, and transparency in data sources and methodology to ensure the outputs support decision making that minimises negative environmental impacts.
The most effective opportunity to address embodied carbon is at the design stage, if opportunities are not taken at the early stages then embodied carbon savings are lost for the entire lifetime of the building. The design team can reduce embodied carbon impacts by considering the following:
• More efficient building design (compact building form)
• Undertaking options appraisal for substantial elements (structure, roof, glazing)
• Select materials with lower carbon intensities (EPDs), reused materials, or those with recycled content
• Select locally produced materials
• Design for less waste on site (off-site construction)
At the construction stage the design team can reduce embodied carbon impacts by selecting materials with lower transport related carbon emissions, such as local sources or re-used materials. On-site, they can specify work procedures and methods to avoid waste and use energy efficient site offices. During this phase they should monitor and evaluate on-site construction to ensure material efficiency and waste management
To address the reduction of embodied carbon impacts at the in-use stage, the design team should select durable materials with low through-life maintenance needs. Their designs should also allow easy reconfiguration and remodelling to meet changing user needs. This should include the easy replacement of some building aspects, and a maintenance, servicing and repair strategy should also be developed.
When considering a building’s end of life stage embodied carbon impacts can be reduced by considering the following:
• Design for reuse
• Design with deconstruction in mind
• Divert waste materials from landfill
• Reuse demolition materials
• Use efficient demolition equipment
Creating and using EPDs for products is voluntary, so being certified with an EPD is not currently standard practice. However, with increasing emphasis on minimising the environmental impacts from building and material use, it is likely that there will be further growth in the number and range of EPDs released. Environmental assessments, such as BREEAM, LEED and HQM, also encourage the use of products with EPDs over those without.
The construction industry should therefore be insisting that manufacturers review the lifecycle carbon of their products and prioritise the use of those with EPDs or those manufacturers that can provide the carbon data for their products. Another way for us to decrease embodied carbon is to design components for building services which encourage disassembly, refurbishment and reuse, or to allow the recycling of components and materials.
Author: Beverly Quinn, Environmental Engineer at TÜV SÜD, an international building services engineering consultancy, specialising in sustainable MEP (mechanical, electrical and public health), BIM (Building Information Modelling), lighting design, and vertical transportation.