We do however know what the current situation of end of life for timber is. Adrian Campbell of Changebuilding reports that, currently, 55% of timber is generally reused at end of life, with 35% used as biomass (combustion for energy), 0% going to landfill, and 20% used in landscaping (for example wood chippings and mulch). Table 4 in the Timber Development UK (TDUK) paper on ‘Assessing Carbon Related Impacts of Timber in Construction’ gives a more specific breakdown, depending on wood product type.
We see opportunity for the end-of-life picture to be improved in the future, with more timber assets being repurposed at their highest asset value as part of a circular economy, i.e., mass timber structural panels able to be repurposed again as structural panels, rather than broken down to layers or as chippings. It is worth noting that where timber is used as biomass at end of life, this can be considered a positive in the short term, because it means we need to use less fossil fuels. But as energy systems move to being more renewably powered, we will need to refrain from combustion – that is unless carbon capture storage has become a truly viable technology.
dRMM considers sequestration as an important part of timber’s embodied and whole life carbon story, and position sequestration as a valid point of comparison when comparing timber with steel or concrete methods of construction, while we are also cognisant of the concerns by some over potential risks at end of life. We agree with TDUK that sequestration should only be counted when timber is responsibly, sustainably sourced from certified forests, to ensure that the carbon cycle is performing as anticipated.
Designing buildings to protect timber structures over their whole lives from moisture and decay is another important consideration. This means that by favouring easily demountable fixings, and with the likely advancements in deconstruction processes that will be made over the next 30-60 years as society moves towards a more circular economy, that it will become unlikely that timber buildings built today will be demolished and then incinerated at all in the long term – particularly as incineration becomes incompatible with the need for decarbonisation. Arguably, in the short term, while our grid is not fully decarbonised, any timber that is incinerated at end of life is substituting a quantity of fossil fuels that would otherwise have been combusted, so is no net increase in carbon emitted anyhow.
Given the urgency of the climate crisis we face, locking carbon into buildings now and in the short term will pay dividends long term. This outweighs the systems that involve emitting carbon upfront and seeking to find carbon storage technologies later. After all, humankind is yet to develop any carbon storage that works better than the tree. The UK’s linear approach to whole life carbon does not adequately tackle the important element of time and urgency that is tied to the climate crisis. In Europe, more dynamic methods of life cycle assessments are being adopted to address these unavoidable parameters.