CQ Blog: Long view of sustainability

10 Feb 2015

Tom De Saulles considers the words ‘green’ and ‘sustainable’. Often used in the same context, but recently with a subtle divergence in their implied meaning.

The words ‘green’ and ‘sustainable’ are often used in the same context, but recently I’ve noticed a subtle divergence in their implied meaning. Green design continues to relate largely to the sourcing and production of construction materials, whilst sustainable design is evolving to more explicitly include a whole-life approach to construction. This recognises that whole-life performance is an important aspect of sustainable construction, particularly in regard to climate change resilience, durability, and embodied CO2. Evidence for this change can be found in a number of places, including the latest version of BREEAM, where credits are available under the new headings of ‘Adaptation to Climate Change’, ‘Functional Adaptability’ and ‘Designing for Durability and Resilience’. There will also be a new overheating category in the housing version of BREEAM due for launch in 2015. Further evidence can be found at a European level, where a recent recommendation has been made for climate change adaptation to be embedded in the suite of sustainability standards linked to the work of TC 350 (which may inform UK standards). There is also a new Innovate UK initiative entitled ‘Building Whole-life Performance’, which will fund and promote work in this area. But, perhaps the most manifest sign is the recent staging of Resiliance14 at the BRE; a major industry event that looks set to be held annually, focusing on flooding, overheating and other resilience issues.

In terms of whole life CO2, Environmental Product Declarations (EPDs) are now being developed for a range of construction materials, including a number of concrete products. As EPDs are based on whole-life performance, which includes end-of-life impacts, they provide a more complete indication of emissions than is possible with the cradle-to-site values that are widely used at present. So over time, building design is likely to place less reliance on this convenient but limited form of CO2 data. The ascendance of EPDs and a general whole-life approach to design is something most practitioners in the construction sector are likely to welcome, including the concrete industry, where the challenge is to ensure that the long-term performance benefits of concrete are adequately accounted for in the design process.

The timber sector has also produced new data for use in EPDs and the lifecycle assessment of UK timber products. The data is in the form of a lifecycle database and shows both the level of CO2 sequestered by timber and the amount released at end-of-life when it ultimately decays or is burned.

With these progressive initiatives going on, it is surprising to see a new campaign by the Forestry Commission, which continues to promote the cradle-to-site CO2 of timber as a basis for specifying timber products. The campaign suggests that replacing one m3 of concrete with the same volume of timber can save around one tonne of CO2. Being a cradle-to-site figure, end-of-life emissions are omitted. If included, you get a different outcome; the new timber database mentioned above shows that over the complete lifecycle of a building, the embodied CO2 of one m3 of timber used in an open panel timber frame system is actually about the same as one m3 of structural concrete, and is higher than that of concrete blocks. For cross laminated timber (CLT) and glue laminated timber systems, the embodied CO2 per m3 is around a third higher than structural concrete. Behind the headline figures is the case for short term CO2 storage that timber provides during the operational life of a building.

In whole-life terms though, the comparative embodied CO2 of timber and concrete construction is largely a non-issue, as it has been shown by several studies that there is negligible difference at the building level. This is because the components and systems that make up the overall design are common to both forms of construction and it is these that account for most of the CO2 footprint. In terms of housing, the most recent study to reach this conclusion is from the NHBC Foundation and is published in a 2011 report entitled ‘Operational and embodied carbon in new building housing’.

Ultimately, it is of course up to designers and specifiers to try and make informed decisions regarding embodied CO2 and long term building performance. To make the task easier, perhaps the starting point should be to test options in terms of their likely whole-life performance; an approach that will become more straightforward as EPDs are produced and whole-life thinking becomes more widely embedded in design and assessment tools.

For more information on concrete and sustainability visit www.sustainableconcrete.org.uk