The science of climate change is well established. It will cause massive, irreversible damage to our world. We need to change now. By building with sustainably sourced timber, we can turn our built environment into a weapon against climate change which absorbs and stores carbon.
Why we need to build with timber
Sustainable forests absorb carbon. This can then be harvested as timber, and stored in our built environment for hundreds of years. The UK Climate Change Commission, Royal Society, and United Nations have all recognised the importance of building more with timber for achieving net zero carbon emissions.
‘Building with biomass’ is acknowledged as an affordable, effective form of carbon capture and storage by the Royal Society, and the Royal Academy of Engineering in their report on Greenhouse gas removal.
The UK Climate Change Commission estimates that if timber were used to build 270,000 new houses, we could increase the amount of carbon stored in UK homes to 3 Mt. This is equivalent to the greenhouse gas emissions which 636,943 vehicles will emit in a year.
This estimate is supported by research from the BioComposites Centre at Bangor University, Wales, which found that using timber frames rather than masonry can reduce carbon embodied emissions by around 20% per building. When cross laminated timber (CLT) is chosen in place of concrete structures the effect is even greater, with carbon embodied emissions reduced by around 60%.
These carbon saving effects of building with timber have been repeatedly found across UK studies. On average, one tonne of carbon dioxide is absorbed and stored for every cubic metre of sustainably harvested timber used in UK construction. The Royal Institute of Chartered Surveyors (RICS) reports that a single five-storey cross-laminated timber (CLT) building can cut carbon emissions by levels equivalent to removing up to 600 cars from the road for a year.
It’s not just structural timber which makes a difference to carbon emissions. Research by Heriot Watt University for the Wood Window Alliance in 2013 estimated that using a timber framed window instead of a PVC-U one saves approximately one and a half tonnes of carbon dioxide per home, the equivalent of driving over 5,000 miles in a small family car.
As explained in the UN Emissions Gap Report 2019, there is a documented tendency for overdesign in larger steelframe structures of around 20–30 per cent. Cement, a major building material, and carbon emitter is often used more than necessary in various applications. Innovation in the timber industry means that timber can often be substituted for both of these materials.
“Building with biomass can both avoid new emissions and provide storage for CO2 captured in forestry. The potential GGR potential from building with biomass through replacement of conventional construction materials is estimated to be in the range 0.5 to 1 GtCO2 pa. It has been claimed that this could save 14 – 31% of global CO2 emissions and 12% to 19% of global fossil fuel consumption… these materials provide an alternative to standard construction materials, including steel and concrete, which are typically carbon-intensive to produce.”
Achieving our climate targets
For the construction industry to play its part in achieving net zero emissions, there needs to be a step change both to how we construct our houses (looking at their ‘embodied carbon’), and though improvements to the energy performance of our homes over their lifetime (their ‘operational carbon’).
Operational carbon has been a focus of policy makers for decades, and continues to be in the UK Government’s Future Homes Standard. As a result, modern homes are better insulated, while the continuing renovation, maintenance and improvement of existing housing stock continues to reduce the amount of energy used for heating in the UK. Combined with the increasing use of renewable energy sources, this means the operational carbon of UK homes continues to decline.
Embodied carbon now makes up an increasingly large percentage of the lifetime carbon emissions of a building. The World Green Building Council is calling for industry to take action to tackle these carbon emissions which are released before the built asset is used, what referred to as ‘upfront carbon’. As these will be responsible for half of the entire carbon footprint of new construction between now and 2050.
The number of new housing stock in the UK is expected to increase by around 25% by 2050. While it is essential these homes have high thermal performance, able to minimise their operational carbon, it is important not to lose site of their embodied carbon cost. Construction which takes hundreds of years to reclaim their carbon debt through energy efficiency are not enough to meet our climate targets.
Many environmentally oriented organisations in the construction industry are taking note with targets to reduce their embodied carbon. The Royal Institute of British Architects (RIBA) Climate Challenge aims to reduce embodied carbon by 50-70% by 2030.
There are examples across the UK where timber is being used more and more as the construction material of choice – for example, the London Borough of Hackney and Powys County Council in Wales both have a ‘timber first’ approach to their planning policies – but the advice of the CCC to favour timber has not been universally adopted to date.
On a national level, there have been agreements between industry and the UK Government in the construction industrial strategy to achieve a 50% reduction in greenhouse gas emissions in the built environment. However, the Government dropped their flagship policy for zero carbon homes in 2015, and there remains a gap in national policies in the UK to address embodied carbon.
“Instead of using reinforced cement, masonry or steel frames, timber, bamboo and other plant fibres can be used as building materials, which has the potential to significantly reduce lifecycle GHG emissions in materials production and carbon storage, even when considering a potential trade-off with operational energy use…Building codes, which have long been used to improve energy efficiency, present a potential model and platform for developing policies that support lighter-weight structures, the reuse of components and timber-based construction.”