Why managing carbon emissions matters
According to the latest Global Status Report for Buildings and Construction, published in 2022, in 2021 the worldwide construction sector accounted for around 37% of global energy- and process-related CO2 emissions and more than 34% of global energy demand.
Materials used in construction of the built environment account for around 10% of total global CO2 emissions, the report adds.
This has led the sector, from clients to architects, developers and occupiers, to look at the impact of the buildings they commission, design and deliver and work in on the world around them.
A building’s environmental impact over its useful life is the subject of ‘life cycle thinking’ – effectively ‘cradle to grave’ – which has coalesced into a building life cycle assessment (LCA), a procedure that looks at a structure’s impact on the environment in its totality.
What is a life cycle assessment in construction?
There are different ways of describing an LCA, and none are exactly the same. The Carbon Leadership Forum’s (CLL) ‘Life Cycle Assessments of Buildings: A Practice Guide’ spells out its take on the matter by listing five life cycle assessment stages and examines how a building’s delivery and use might affect the environment.
The report first identifies a ‘production stage’, which features the energy and resources used to extract raw materials, to transport those materials to product manufacturing facilities and then to produce the final building products.
The ‘construction stage’ involves the transportation of those materials to the construction site, the energy used to power the construction equipment and supply supporting construction materials, and to dispose of any waste generated during the construction process.
The ‘use stage’ of a life cycle assessment considers how the occupancy of a building over its lifetime – lighting, heating, water use and any materials used for maintenance, repairs and replacement – affects the environment.
The ‘end-of-life’ stage involves the demolition and disposal of the building as well as waste processing, assuming the building is not repurposed or improved for further occupancy or use. Finally, there is what the CLL calls the impact of ‘miscellaneous effects of reusing, recycling and/or recovering materials, energy or water from the project’.
Benefits and limitations of conducting an LCA
While a life cycle assessment can help clients, occupants and planning authorities make more informed decisions during the design and building processes, it can also drive innovation by revealing opportunities for manufacturers to improve a product’s efficiency and quality.
According to Green Building Solutions, which is part of the American Chemistry Council, contractors can know how to better prevent or resolve environmental problems related to project management and improper waste disposal, while building owners can see how sustainable products favourably reduce environmental impacts during the lifetime of their investment.
Building life cycle assessments do have their limitations, however. Environmental training provider Envirotrain suggests the scope of an LCA might not be extensive enough to consider all the likely environmental impacts of a building. Moreover, elements such as biodiversity can be difficult to quantify.
Secondly, there isn’t an accepted single LCA methodology, with some studies choosing to focus on individual stages of the various processes – extraction, delivery, construction and useful life – rather than the overall life of a development.
Also, says Envirotrain, some assumptions about the likely impact of certain materials or processes might be subjective, and the quality of data might be questionable.
Are there national guidelines for life cycle assessments?
With such caveats in mind, how can people be assured of the usefulness of an LCA when considering their project?
In the UK, the Royal Institution of Chartered Surveyors (RICS) has published a whole life carbon assessment (WLCA) standard, which ‘sets out an RICS-approved technical methodology for assessing the carbon impacts from buildings and related infrastructure assets / civil engineering works throughout their life cycle’.
Some highlight that embodied carbon – the carbon embedded in a structure’s materials – isn’t subject to enough scrutiny. The UK Green Building Council’s (UKGBC) Net Zero Whole Life Carbon Roadmap states that ‘the accurate and consistent measurement and reporting of embodied carbon has become increasingly important to ensure meaningful and credible progress towards net zero carbon goals’.
The UKGBC says it is essential that embodied carbon ‘moves quickly from being a challenge only addressed by leading organisations to one that is tackled by stakeholders across the built environment industry’.
In Canada, the country’s National Research Council has produced a series of guidelines for whole building life cycle assessments (wbLCA).
The NRC says the purpose of the guidelines is to ‘instruct wbLCA practitioners to assure quality and comparability of their results; enable the calculation of reliable baselines or benchmarks; support the LCA-based compliance schemes in green building programs and policy, and assist in the development and use of wbLCA software’.
Helping construction professionals make more informed choices
While not perfect, the life cycle assessment will increasingly play an important role in driving a built environment that has less impact on the world around it.
In the U.S., the Carbon Leadership Forum argues that LCAs can help designers and building owners make informed choices around sustainability and resilience of materials and design options. They can also help with gaining a green certification for a building and compare to established benchmarks to evaluate a building’s performance.
Some critics point out that LCAs often miss things like context – geographical location, etc. – and that a building should be competing with itself to drive toward the best solutions in any given situation.
But given the importance of reducing carbon emissions, the direction of travel for the industry favours the implementation of LCAs.
The growing influence and importance of green certification programs such as LEED and BREAM shows how seriously the industry and its client base take the issue.
Irrespective of imperfections, LCAs provide a meaningful way of judging the impact of a building on its surroundings. We are likely to see more of their like in the coming years.