The reduction of carbon emissions in the UK has become increasingly important since the government’s net-zero 2050 target was announced. The built environment is responsible for almost 40 per cent of the UK’s carbon emissions and is therefore one of the key sectors required to reduce emissions.
A whole life carbon (WLC) assessment – an assessment of the sum total of all building-related emissions over a building's entire life – is the most comprehensive approach to achieving these reductions. WLC includes operational carbon emissions from day-to-day energy use and embodied carbon emissions, including material sourcing, fabrication of components, transport, construction, maintenance, repair and replacement, demolition, dismantling and disposal. The objective of a WLC assessment is to ensure the minimum overall lifetime carbon emissions and the maximum lifetime resource efficiency.
The structure of a WLC assessment is defined by British Standard BS EN 15978:2011. The standard breaks down the life cycle of a building into life cycle modules, but it is not sufficiently precise or informative about how a WLC assessment should be undertaken. In 2015, a group that I led – and included representatives from RICS – received funding from Innovate UK to provide a detailed methodology for a WLC assessment. As a result, RICS published the Whole life carbon assessment for the built environment professional statement in 2017 and it became mandatory and regulated by RICS in May 2018.
The professional statement gives guidance on a range of issues involved in a WLC assessment including spatial boundaries, units of measurement and carbon sequestration. It also explains how to assess each of the following life cycle modules:
For an assessment at the RIBA Plan of Work stages two or three, actual materials and systems will not be known with any precision, and therefore the professional statement offers default figures to be replaced by project related figures as the project progresses.
A life cycle assessment (LCA) – a future projection of the carbon cost of anticipated day-to-day energy use, maintenance cycles, repair and replacement cycles and final demolition – is inherent in a WLC assessment and is usually presented as a graph showing annual carbon emissions over 60 years. The objective is to understand, at the design stages, the overall future carbon emissions performance of a building over its entire life, and therefore what can be done to decrease emissions. In addition to the mapping of anticipated future carbon emissions, it is possible to add a cashflow to the LCA to give a building owner a combined construction and 'In-use' cost, that is, a total cost of ownership.
The alignment of carbon cost and financial cost is not surprising as their reductions both rely on an efficient use of resources. Typically, for the 'Upfront' carbon costs –those embodied emissions up to practical completion covered in modules A1-A5 – the better carbon options also have lower costs.
"The alignment of carbon and financial cost is not surprising as their reductions both rely on the efficient use of resources"
My company, Targeting Zero, reviewed tender returns from an embodied carbon perspective for a global technology company's new headquarters and found that the lowest carbon and lowest financial cost aligned in every case. Several major London-based developers now see 'Upfront' embodied carbon assessments as part of value engineering and, therefore, contributing to reduced construction costs.
By also considering 'In-use' carbon costs – modules B1-B7 – it is possible to examine the carbon cost of fabric improvements against the carbon benefits of improved energy performance. This is important as it shows that operational energy use should not be viewed independently from embodied emissions: to optimise overall emissions, both operational and embodied emissions need to be considered together.
For example, when selecting insulation, the decision should be based on both the U-value, or thermal transmittance, and the carbon dioxide equivalent emitted per square metre – KgCO2e/m2 – to make the material. This material and product-related carbon footprint information can be obtained from Environmental Product Declarations (EPDs) – there are now over 7,000 EPDs available for individual products.
A further benefit of understanding 'In-use' emissions is that future performance can be determined in relation to different factors, such as lease cycles or climate change. The more durable and resilient the design, the lower the post-completion carbon impact will be.
"The more durable and resilient the design, the lower the post-completion carbon impact will be"
Following an initial WLC assessment, there are several actions that can be taken to help reduce the WLC footprint of a building.
The retrofit or reuse of an existing building – as a whole or in part – is preferable to a new building as it is typically the lowest carbon option. A retrofit has a significant embodied carbon benefit due to the existing structure and materials already on site.
Using recycled materials and content
Using recycled materials as opposed to newly-sourced raw materials typically reduces the carbon emissions from constructing a new building. Many currently available standard products already include a degree of recycled content, and therefore the supply chain should be encouraged to provide the project team with this carbon footprint information.
The sourcing of materials and the fabrication of products is the single largest contributor to embodied carbon emissions over the life of a building. It is important to note that the overall lifetime carbon footprint of a product can be as much down to its durability as to what it is made of. For example, bricks may have a high carbon cost to make but they have an exceptionally long and durable life expectancy.
Operational emissions from day-to-day energy use
A fabric-first approach where the building’s envelope is designed to minimise heating and cooling requirements can have long-term carbon emissions benefits. A naturally ventilated scheme avoids the initial carbon costs of new plant and distribution, as well as the repeat carbon costs of equipment replacement.
Reuse of a building’s components at end of life
Designing for future ease of dismantling, rather than normal demolition, means that materials and products can be reused for the same purpose as originally intended. A simple example is to use lime mortar with brickwork rather that cement. The former can be cleaned off allowing the brick to be used as a brick, whereas the use of cement mortar means the bricks end up as landfill. The choice of recycled materials in combination with designing for future reuse contributes to the circular economy.
Wall to floor ratio
Also known as the heat loss form factor, wall to floor ratio has embodied as well as operational consequences; compact and efficient buildings perform better for these reasons.
Durability and future flexibility
Considering these at the outset of design reduces maintenance and other life cycle costs and facilitates future retrofit, therefore reducing the likelihood of future obsolescence. Every project brief should have a building design life specified, with a requirement for method statements for future repair and replacement as part of the procurement documentation.
Embodied and operational emissions
Optimising the relationship between the two types of emissions is important to ensuring whole life carbon reduction efficiency. The objective is to understand, over a building’s life, the carbon cost as well as the carbon benefit of any action to improve its performance. For example, the use of insulation has a clear carbon benefit, whereas its fabrication has a carbon cost. This means that it is important to look not only at the U-value of insulation, but also the carbon cost of the manufacture and installation of different product options.
This reduces transport distances and therefore supply chain lengths. It also has associated social benefits including, for example, local employment.
This is a key feature of low carbon design and procurement through all life cycle stages and means understanding how materials and systems are sourced and fabricated. Building designers must understand how products are assembled on site to ensure minimum waste.
Construction techniques such as using modular systems, precision manufacturing and modern methods of construction can contribute to a reduced construction carbon footprint due to more efficient fabrication, and reduced snagging and early replacement.
Many of the above principles require actions – by developers and project teams – that may be seen as of limited benefit to the developer in the immediate future. There are three key arguments that can be used to convince developers of the benefits of investing in a low carbon approach.
First, most of the principles listed above don’t necessarily add to construction costs – and many will actually reduce the total cost of ownership. Second, it is very possible that if the valuation of buildings starts to include climatic resilience and performance and an LCA as part of due diligence carried out then these actions will become essential. Finally, being ahead of future regulation change will reduce building obsolescence and therefore benefit developers in the long term.
Since the publication of the professional statement in 2017 numerous organisations – including British Land, Landsec, Derwent, Grosvenor, the Portman Estate, Warwick University and Quintain – have embedded its guidance in their practices. It is also being used on HS2 and the latest Heathrow expansion to mitigate carbon impacts.
Other documents such as RIBA's Embodied and whole life carbon for architects, the UKGBC's Net zero carbon buildings: a framework definition and London Energy Transformation Initiative's Climate emergency design guide all make direct reference to the professional statement. The Mayor of London also explicitly referenced the professional statement in the London Environment Strategy, released in May 2018.
At the time of writing, the Greater London Authority's London Plan is being updated and will require all referable schemes – including developments of 150 or more residential units, developments of more than 30 metres high outside the City of London and developments on green belts or metropolitan open land – to carry out a detailed WLC assessment in accordance with the RICS professional statement and BS EN 15978:2011. These will be required both on submission of the scheme and post-completion. The detailed guidance in the London Plan also suggests that WLC assessments will soon be a requirement on all submissions in the near future. Other UK local authorities are likely to follow the example of the London Plan and tighten up all existing building and planning regulations.
For those buildings currently on the drawing board, sticking to the current regulations may be a bigger risk than future proofing the asset value of your building with a WLC assessment and resulting actions to reduce its whole life carbon footprint.
The fact that the London Plan guidance is about assessing the entire life cycle of a building will help clients better understand overall lifetime performance in both carbon terms and cost terms. This will affect how buildings are valued, with a WLC assessment becoming a fundamental part of due diligence in assessing future asset performance and value.
Further, climate change is increasingly becoming a consideration from the perspective of investment and insurance risks, and the likely impact it may have on occupier sentiment. Buildings that are not climate friendly, or low carbon, are likely to be at a disadvantage in the future. There are several international organisations, such as the World Business Council for Sustainable Development (WBCSD) and the Principles for Responsible Investment (PRI), that are advising both investors and insurers on the implications of climate change.
The PRI states: 'As part of wider efforts to implement the Paris Agreement, every real estate asset owner, investor and stakeholder must now recognise they have a clear fiduciary duty to understand and actively manage ESG [environmental, social and governance] and climate-related risks as a routine component of their business thinking, practices and management processes.'
The next steps for WLC assessment and reporting will be to gather more building-related data – the London Plan requirements will greatly assist in this. Further measures are required to ensure consistency of reporting, and these need to feed into the available assessment software that currently produces different answers from different types of inputs.
It's important to remember that the environmental landscape when the Whole life carbon assessment for the built environment professional statement was launched was very different to how it is today. However, it is encouraging that, although further work needs to be done, the importance and necessity of WLC assessments has become far more widely understood over these past three years.
Related competencies include: Construction technology and environmental services, Sustainability
Prof. Sara Wilkinson FRICS, Dr Gill Armstrong, Dr Kusal Nanayakkara, Mark Willers FRICS, Prof. Jua Cilliers and Dr Robert Fleck 08 December 2023