Footprint reports from the ASBP’s recent conference on carbon sequestration in buildings
The Association of Sustainable Building Products (ASBP) recently organised a policy seminar on the thorny subject of sequestered carbon in buildings. Various industry experts spoke about what it is, how it should be understood and how it should be integrated into the design process to create better, more environmentally beneficial, buildings.
Professor David Robson - Resource Efficiency Services
Jonathan Fovargue - Eurban
Andrew Waugh - WaughThistleton Architects
Dr Nick Atkinson - Woodland Trust
Jane Anderson - PE Consulting
Ian Pritchett - Lime Technology
Graham Hilton - ASBP
The basic concept is that carbon that might otherwise form carbon dioxide in the atmosphere is stored in biogenic materials such as timber, hemp, sheep’s wool, straw, recycled paper etc. When a building is constructed from biogenic materials and the harvested plants are replaced, the building becomes a form of carbon storage. The carbon in the materials is locked up until the building is demolished and the biogenic elements are destroyed. The relatively long lifespan of buildings make them an ideal place to lock away carbon in a way that can be observed and measured.
Many speakers highlighted the fact that sequestered carbon is rarely addressed in discussions on the built environment. The focus of the environmental impact of buildings has been concentrated on the operational carbon emissions and to a lesser extent the embodied carbon. The notion that biogenic materials in a building could make a positive impact to the level of greenhouse gas concentration in the atmosphere rather than just being less bad, is seductive. Responsibly increasing the use of biogenic materials in construction can result in the storage of more carbon in our built infrastructure and if managed correctly should stimulate the creation of more forests.
It is not yet common practice to integrate the carbon capturing qualities of biogenic materials into the design process. Professor David Robson of Resource Efficiency Services noted that the Green Guide is too pessimistic about the carbon storage potential of timber products. This is set to change because harvested wood products have been included in the calculations of country greenhouse gas emission inventories under the Kyoto Protocol since 2011. Professor Callum Hill of Edinburgh Napier University explained that carbon sequestration will now be taken into account when setting Product Category Rules (PCR) for timber product. PCRs are the basis for Environmental Product Declarations (EPD).
Environmental Product Declarations (EPD):
EPDs provide specific information about the embodied carbon of a product from cradle to gate. This will allow designers the ability to make informed decisions about the embodied carbon of their proposals based on actual, not generic assessments. Based on a European standard EN15804, defining industry standard product category rules, the EPD allows consistent and product specific between similar products.
Product Category Rules (PCR):
A consistent set of rules on which EPDs are made. These rules define the calculation methodology and indicators so that comparisons can be made consistency. Within the EU these are according to the new standard EN15804.
For a building to become a net carbon absorber a number of conditions need to be satisfied. The biogenic materials that are harvested for the building need to be replaced in equal or greater quantities in order for a net gain of carbon storage. The carbon emissions from transporting and processing biogenic materials into usable products need to be lower than the amount of carbon stored in the material. Furthermore the operational energy use of the final building should not be significantly compromised by using a biogenic material as this could also undermine the positive effect of carbon storage.
Two projects show how architecture can become a carbon store. Andrew Waugh of WaughThistleton presented Murray Grove, a nine-storey residential building in Hackney, constructed in cross-laminated timber (CLT), a net improvement of 1260 tonnes of CO2 in using CLT in the place of concrete. Jonathon Fovargue, of specialist timber contractor Eurban, spoke about Bridport House, an eight -torey residential building designed by Karakusevic Carson Architects. His data showed that total difference of CO2 released into the atmosphere between a concrete frame and CLT construction was 2044 tonnes of CO2 which is equivalent to 27 years of the predicted operational carbon emissions for the scheme. Both Waugh and Fovargue spoke about CLT’s other positive qualities. It is significantly lighter than its concrete frame equivalent and it is prefabricated off-site which makes the onsite construction schedule shorter and consequently cheaper. The only drawback is that most CLT is currently produced in Austria and transported by road. As more UK practitioners adopt CLT, UK production is likely to become viable.
All the speakers on the ASBP panel made a compelling case for sequestered carbon to be factored into the design process. The best possible outcomes will result from coordinated action from across the industry. Forestry, currently the UK’s fifth biggest industry, will need to expand in order to meet demand. Current UK forestry policy has returned woodland to the same levels as the 16th century and now accounts for 12% land coverage in comparison to 44% for the rest of the EU. The potential benefits for lower carbon construction, job creation and reforestation presented in this seminar make a strong case for greater consideration of sequestered carbon in the design process.
The ASBP’s draft policy paper and presentations on sequestered carbon are available here.
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