The use of timber in the built environment – is it beneficial?

We are quite used to sitting at timber conferences and listening to the familiar story – the use of wood in buildings is good for the environment, because it stores carbon and can be used as a substitute for higher embodied-energy materials. We all agree and go home with that nice cosy warm feeling and look forward to the next conference. However, there are other opinions expressed by other sectors, which do not share this view. What is it they are saying and how valid are these alternative viewpoints? How can we discern fact from opinion or misinformation?
The intention is to focus on one aspect of the use of timber in the built environment, the storage of atmospheric carbon, and examine how the use of inappropriate models can lead to a great deal of confusion regarding the potential benefits of using timber as a carbon store in long-life products. The current ‘+1’ ‘-1’ approach being a good example, apparently showing that there is no benefit of using timber from a carbon storage point of view.
Conventional life cycle analysis cannot deal with the temporal aspects of carbon storage and attempts to deal with this problem in the past have led to variations of discounting methods, which have not been accepted in the various standards that deal with these issues. One potential approach is to adopt dynamic-LCA, but this makes a complicated subject even more complex and is mainly of interest to the academic community.
It will be shown that the best way of dealing with the issue of time of storage of carbon in products is to use materials flow analysis (MFA). This allows the residence time of a population of products (buildings in our case) in a carbon pool to be modelled using decay functions. The main issue when using such an approach in the real world is to determine what the statistics of building lifetimes really is. Most recommendations rely on simple exponential decay functions, which are wholly inappropriate and use very questionable half-lives. There is an urgent need to use better decay functions and use parameters that are based on facts rather than assumptions.
However, using these models, it is very easy to show that life extension of timber buildings has a positive effect on the storage of atmospheric carbon. Doubling the lifetime leads to a doubling of carbon stored. The potential for the use of timber in construction as a climate mitigation strategy is clearly demonstrated using this approach.