By Dave Hopkins, director at Wood for Good, the timber industry’s sustainability campaign
The merits of timber construction have been rapidly gaining appreciation in the housing sector over the last decade with the market share of timber frame rising from just over 14 per cent in 2001, to approaching a quarter of today’s newbuild market.
The time and cost-savings offered by off-site engineering along with the increased precision and quality of the finished product have driven much of this growth. The environmental advantages – from being a low-carbon, naturally renewable material, to its unrivalled insulation properties – have also seen timber grow market share in the green building market. However, while many specifiers have long been convinced of the various benefits of timber, they have lacked the empirical evidence to endorse its use.
To address this, the industry has created a Lifecycle Assessment (LCA) database bringing together environmental performance information on a range of wood products commonly used in the UK in a single, convenient hub on the Wood for Good website. It includes data on every aspect of the life-cycle of timber products, from forestry, harvesting, transportation, processing and manufacturing, through to the various end of life options.
Now, architects and specifiers are using the data to model forthcoming projects. It’s allowing them to benchmark timber products’ environmental impact in terms of things like embodied carbon or global warming potential and allowing us to shed new light on the environmental qualities of existing buildings.
One particularly compelling example of timber in action was the construction of Bridport House in Hackney. The building was one of the UK’s first multi-storey buildings to be constructed using only timber and its largest cross-laminated timber (CLT) residential scheme. The CLT material was chosen, in part, due to the speed at which the building could be constructed on-site (12 weeks on-site, six less than if traditional frame construction).
The building was originally designed in concrete to replace an older, existing concrete block. However, a combined sewer pipe was discovered running directly beneath the site. If the building had been rebuilt in concrete to today’s much higher performance standards, the building would have been so heavy that major reinforcement and foundation work would have to take place to prevent the pipe from being crushed.
As a much lighter weight material, timber was chosen allowing the project to build higher on the existing foundations. Not only that, but it has low carbon advantages too. Trees absorb carbon dioxide as they grow storing it in wood. The eight-storey Bridport House tower features 41 socially-rented affordable homes. In total they store a significant 1,100 tonnes of CO2. Had the building been constructed using reinforced concrete, the amount of carbon emitted in its development would have been 892 tonnes – to put this into perspective, this would be the volume emitted in heating and lighting all of the homes in the building for 12 years.
With regulatory and legislative frameworks for construction becoming ever more restrictive, the assessment of environmental impacts are set to become increasingly important customer drivers, alongside cost and performance. The latest EU climate change targets (a 40 per cent reduction in emissions across the EU and up to 30 per cent energy efficiency improvements) agreed in October are also likely to usher in a renewed focus on the sustainability of the built environment.
As part of their efforts to meet these targets, the government has started to mobilise investment from a £1 billion pot set aside to fund Carbon Capture and Storage (CCS) projects. However, we have argued that the proven natural carbon capture capabilities of wood would provide for an additional use of the investment and can help tackle the UK’s emissions from within the construction industry.
Using research from the LCA, it was found that one average three-bed, timber-framed house stores 19 tonnes of CO2 in the timber products used in its construction. By scaling this up it was demonstrated that an average estate of 84 houses would store 1,602 tonnes of CO2. If Labour’s housing target of delivering 200,000 homes annually was actually met, 4 million tonnes of the greenhouse gas every year could be stored.
LCA studies show that timber products absorb and store more carbon dioxide than they emit as a result of their entire manufacturing process – including harvesting, kilning, processing and delivery – arriving on-site with a carbon negative footprint. These qualities mean timber effectively offers the construction industry the option of going from emitting carbon to building with it.
Building with timber is the safest and cheapest form of CCS available and is arguably a more effective way of contributing to new emissions targets than unproven CCS technology. It is estimated that it costs roughly £25-30 per tonne of CO2 captured and stored using mixed woodland forestry. However, unlike other finance models, this is not ‘in addition’ to the process, it is already paid for as an inherent aspect of the timber. With a wealth of data on various timber products accessible in one place, the creation of the LCA is set to usher in a new era of sustainable construction.