We need a level playing field for calculating carbon, says Jenny Smith-Andrews, head of marketing at H+H UK, as she explores the complexities of sustainable construction
There is unilateral agreement in the construction industry that more housing is required and that this housing must be built sustainably. Yet the definition of sustainable construction remains a topic of debate.
We believe the focus should be on building high performing resilient homes with low whole lifecycle carbon.
The debate is currently centred on embodied carbon, an important part of the equation but one that can only be meaningful with a level playing field for calculating embodied carbon. Only when we have standardised methodologies for measuring and reporting embodied carbon can we conduct accurate comparisons of different building materials and methods.
Looking at the whole picture of sustainable construction
If specifiers are to make the right choices for creating sustainable buildings, they need to make sure they are comparing like-for-like.
The construction industry relies on established guidelines and technical guidance in the form of product category rules (PCRs) and environmental product declarations (EPDs).
Comparing EPDs for different products can be complex as there are elements that may not be consistent from one EPD to another. For example: different methodological approaches may be taken; generic rather than product-specific data may be used; different units of measurement may be used; and non-required fields may be included in some EPDs and not others.
It pays to look closely at the numbers rather than any commentary. The focus should be on “whole life” or “cradle-to-grave” carbon emissions. Our EPDs report the full lifecycle of our products as we believe that any embodied carbon figure quoting only the “upfront” or “cradle-to-gate” manufacture is not a true reflection of the environmental impact of that product.
Inconsistencies in information contained in an EPD can have a major impact in terms of product specification. This is particularly true when comparing biogenic products such as timber with products manufactured using other materials.
This is highlighted in a report published by engineering consultancy LBP SIGHT, which analysed 48 EPDs for wood products.
The report Carbon Accounting for Building Materials – An Assessment of the Global Warming Potential of Biobased Construction Products, states: “The assessment of PCR and EPDs of wood-based products shows that inconsistencies both at the system level of PCR and the implementation in EPDs exist. Ultimately, this results in skewed declared values for CO2e emissions at the product level, and therefore in comparison with alternative products.”
Product EPDs that contain biogenic carbon are required to be modelled on their full lifecycle. The RICS Whole Life Carbon Assessment (WLCA) for the built environment does allow for cradle-to-gate EPDs, but only if biogenic carbon is totally excluded.
It is worth noting that an older requirement, dating back to 2013, allowed cradle-to-gate for biomass materials. This has allowed some timber products to report carbon credits instead of impacts, which can be misleading where legacy EPDs are referenced.
Taking a practical approach to sustainable construction
Specification decisions can be influenced by assumptions and an emotional response to different materials. Setting aside this emotional element and focussing on the evidence produces comparable figures.
However, sustainability is not just a single number, it’s a complicated argument. There have been calls for more timber to be used in construction, but is that truly the answer? The UK imports around 80% of its wood, making it the world’s second largest importer of wood after China. Offshoring the UK’s wood supply to this extent creates supply chain vulnerabilities.
As the global demand for timber surges, this problem is set to get worse. The World Bank estimates that global timber demand will quadruple by 2050, which may create challenges for sustainable timber production, and potentially issues for longer-term decarbonisation.
To mitigate these issues, there is a push to increase homegrown softwood timber. However, we are nowhere close to being able to meet current demand and will fall even further behind as we increase the amount of timber used in construction.
Given the length of time it takes to grow timber suitable for structural purposes, this has put the UK on the back foot in terms of having homegrown structural grade timber to use in the near future.
In fact, the time needed to substantially boost the production of construction grade timber will allow other industries to decarbonise their own production processes.
Masonry materials such as aircrete may have been overlooked in the sustainability debate but should not be underestimated.
We are working towards decarbonising our manufacture process and as the UK moves to more renewable energy sources, the embodied carbon number for aircrete will change, whereas the embodied carbon number for timber is likely to stay the same.
In addition, our supply chains are short, with our Celcon blocks produced using locally sourced raw materials, in factories based in the UK.
Sustainable construction demands a pragmatic approach grounded in evidence and rigorous measurement. Reducing whole lifecycle embodied carbon, simplifying supply chains and enhancing the longevity of housing stock are all critical steps toward meaningful progress.
By adopting standardised methodologies for assessing embodied carbon and ensuring comparisons are made on a like-for-like basis, the industry can make informed choices that prioritise true sustainability.
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