28 April 2021

How to meet the ‘Net-Zero Carbon Buildings’ agenda by building in timber

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2020 was not only the hottest year on record. It was also accompanied by an intensification of natural disasters appearing across the world, including: devastating flooding following heavy rainfall events and prolonged monsoon seasons; a record number of Atlantic storms as well as some of the strongest storms documented, all possibly caused by record ocean heat; and record wildfires across California, Australia, Siberia, and the Pantanal.


There is no doubt that the climate emergency is already having an impact on every inhabited continent – impacting biodiversity, and causing displacement to both humans and animals – but we are all experiencing these impacts to differing degrees.


Within the construction industry specifically, we have our own work to do. We have made great headway on reducing operational carbon in the built environment, but as operational carbon reduces, so too does the relative significance of embodied carbon increase.


Embodied Carbon: Guidance for Welsh Social Housing Developers, their design teams, contractors and suppliers

Woodknowledge Wales recently issued the new guidance document Embodied Carbon: Guidance for Welsh Social Housing Developers, their design teams, contractors and suppliers as part of their Home-Grown Homes project. In its foreword, Gary Newman, CEO of Woodknowledge Wales, said:


“Currently, around 50% of carbon emissions from new build housing is caused by the building materials, the build process, maintenance and end of life – known as the ‘embodied carbon’ emissions. These carbon emissions currently fall largely outside the scope of current regulation.”


It is because these embodied carbon emissions fall outside the scope of current regulation that we must seek to meet the net-zero carbon buildings agenda as a matter of organisational policy by willingly assessing and reducing the embodied carbon of our projects.


Calculating these emissions as early on in the design and build process as possible allows us to maximise their reduction, whether that involves adjusting the building form and construction type, incorporating reuse materials and retrofit, or minimising waste. The Embodied Carbon report compares the various tools currently available to support this process, and highlights a wide range of carbon reduction strategies grouped by the RIBA stage for which they are most relevant.


Biomass, biogenic carbon sequestration and carbon storage

Yet we also have our own low-carbon, environmentally-friendly building material at our fingertips.


Biomass based building materials such as timber contain sequestered carbon, which is CO2 removed from the atmosphere and incorporated as biogenic carbon into biomass through sequestration. (Chapter 6 of the Embodied Carbon report is dedicated to this subject.)


If the tree is harvested, the sequestered carbon within the timber stays as biogenic carbon content until the timber is burnt or decays. At the end of a timber building’s life, however, the timber can still be salvaged and further reused or recycled; if so, the carbon remains sequestered.


The Embodied Carbon report states:


“For most timber, half the dry mass of the timber is biogenic carbon, for example 1 m3 of UK grown kiln dried timber contains 208 kg of biogenic carbon having sequestered 763 kg of CO2 which it then stores out the atmosphere.”


This is significant, if one considers that this carbon will remain sequestered until the end of the timber’s life, which may be hundreds of years. Consider the wooden door in Westminster Abbey an example; when dated for the first time in 2005, it was revealed that the wood used was felled after 1032 AD and the door constructed sometime in the 1050s.


Furthermore, timber is a renewable resource if it is sourced from a sustainably managed forest under a certified scheme such as PEFC, FSC, or Grown in Britain.


Environmental Product Declarations (EPDs)

In order to meet embodied carbon targets, we need to procure products low in embodied carbon. We must seek to obtain Environmental Product Declarations (EPDs) – which provide environmental information about a product in a standardised format using a consistent methodology – in order to make informed decisions about the products we are specifying.


For products where lots of manufacturers have an EPD, such as insulation, you might specify on the basis of the embodied carbon, along with information provided about the biobased and recycled content of the product. These provide the most accurate assessments of the embodied carbon and there are now thousands of EPDs for construction products – yet we still have options where EPDs are not available, or where the exact supplier is not yet known.


The Wood for Good Lifecycle Database and the Inventory of Carbon and Energy (ICE) Database provide two alternative sources of information. Although completed in 2013, the Wood for Good dataset is still very relevant because it is more complete and contains all impacts required for an EPD, not just carbon. The ICE dataset, in contrast, includes more up-to-date information on carbon, showing that manufacturers on average look to be reducing their emissions. For example, Glulam, MDF, OSB and Chipboard emissions all show lower embodied emissions than the earlier Wood for Good data. However, to obtain the most accurate information for your project, be sure to obtain the EPD for the actual material you are using once the specification is set.


If you want to reduce the embodied carbon of your next project, be sure to download and read the Embodied Carbon report from the Home-Grown Homes project. It is one of the most comprehensive, applicable reports compiled on embodied carbon and will be an invaluable resource.


This article is the start of a wider piece of work on timber and embodied carbon in conjunction with Timber Development UK (TDUK), with more to come over the coming months.