Wood First Debate – Sequestering Carbon

Those of you who follow my Twitter feed will have noticed that I attended the ‘Wood first Debate’ last week organised by the UKGBC at the Museum of London. Hattie Hartman of the AJ covered it here.

There was a good discussion once we moved on from the various industry materials groups trying to score points off each other and only ending up sounding trivial. Designers, like me, don’t want to spend our few spare evenings listening to that nonsense, we want to have an intelligent discussion and debate. If the steel, wood, masonry and concrete reps want to have a face-off, by all means do, but not in front of the industry, its embarrassing!

The main point that I took away from the event is that there is no shared understanding about the potential for Environmental Product Declarations (EPD’s) to provide designers with clear information that they can use to compare different materials and products from a life-cycle impact perspective. The sooner that the industry gets comfortable with using them, and the sooner that the supply chain provides them, the easier it will be to make learned choices. Lifecycle impact is only one of many factors in the choice of material, but it is becoming an increasingly important one as we move towards very high fabric performance and start to look elsewhere for further CO2 emission savings.

There was a very detailed and rather difficult point raised about the use of carbon sequestration. This is the concept that carbon dioxide is stored in trees and then in wood products, effectively removing it from the atmosphere, the CO2 is considered to be ‘sequestered’. However, there are carbon accounting methods that allow the countries that grow the timber to benefit from carbon saving finance by counting the tonnes of carbon dioxide locked up in their trees, but which only count while the trees are growing. Wood products are not counted as these are considered to be temporary and will have a short life. If we wish to count the carbon locked up in timber structures and products, in some senses we are double counting as it has already been counted for while the product was a tree. Accounting for products that change hands and move from country to country adds another level of complexity. When a timber product from Indonesia to China, does the Chinese footprint reduce by the amount of CO2 stored in the product, minus the CO2 taken to transport it there?

It would appear that the sensible approach is to take the CO2 savings in the country where the tree was grown, and leave it at that. Unless a way can be found to estimate the carbon savings from the building over its lifetime. Or to routinely make the carbon storage permanent, e.g. by locking in the CO2 by turning the wood products into biochar at the end of their lives and burying it.

A document produced by the Government of New South Wales argues that the CO2 savings from productive forests can be greater than those of conserved forests, if the life-cycle carbon savings of the wood products are correctly accounted for. This includes the carbon stored in wood products and the offsetting of the production of other higher impact materials such as steel and concrete. In this scenario, the country managing the productive forest claims the carbon credit for storing the carbon in the tree up to the end of its life, and the country using the product claims the carbon stored for the life of the product, less the carbon used to manufacture and transport it. This accounts for the additional benefit that wood products offer from productive forests over a forest that is simply managed and maintained.The difficult part is how long that carbon credit should last. For wood furniture its probably 10 years, for wood structures its probably 100 years. At the rate we are replacing housing in the UK, it is currently 1000 years!

This way of accounting for carbon savings is not very different in principle from the current position in the UK where biomass burning is considered to offset the burning of fossil fuels in the National Grid and allows buildings burning biomass to gain a high carbon reduction in their energy use. The term of carbon offsetting considered in the Allowable Solutions framework is thirty years, a timespan that most timber products can comfortable exceed.

In order to resolve this issue we need more effective ways of comparing the carbon in the life-cycle of construction materials and products. Environmental Product Declarations seem to me to offer this opportunity, and we need the supply chain to deliver them to us.

In addition to this we need policies that make it attractive to designers and constructors to take a life-cycle carbon accounting approach to design. While life-cycle impacts are only one of several factors that need to be considered in the design process, it is an increasingly important one as operational carbon savings become harder to find. This is another area where the UK can show leadership by innovating and demonstrating and then selling this expertise around the world.


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