Wood: waste not, want not

Materials World magazine
,
3 Oct 2016

Peter Wilson examines the role of timber in the UK’s energy mix, from consumption to power.

Arguably, almost every building type can now be formed from wood. Recent – and credible – design explorations for tall timber residential structures rising as high as 80 storeys might be deemed over-ambitious and beyond current technological reach. However, concepts such as these stimulate highly advanced structural engineering R&D, and the results filter into more mainstream engineered timber construction. 

The building types – not civil engineering structures, such as dams – that are the most obvious exceptions to this new rule are undoubtedly those facilities associated with the generation of nuclear power. Traditionally, their construction has consumed enormous quantities of in situ reinforced concrete. The 14,500m3 of this material in the foundation work currently being completed at the Hinkley C site is the most immediate example of this tried and tested technological approach. However, the process used in the production of the cement required to manufacture concrete is one of the world’s largest contributors to greenhouse gases. That calculation should arguably be set against the anticipated carbon efficiency of the nuclear facility once it is up and running.

The new world

We now live in a world where other options are not only possible but, for many, also broadly desirable. Whether for economic, environmental or sustainability reasons, the search for alternatives to fossil fuels to generate energy continues apace, as does the debate between the advocates of nuclear power and those who would give primacy to the development and application of renewable sources of electricity and heat. Ever increasing consumption of energy – especially in the world’s more developed economies – can also be directly correlated to profligacy in its use. Instead of implementing approaches that reduce energy requirements, we simply seek more effective ways to produce greater amounts of what is nowadays considered to be an indispensable human requirement. 

Of course, in the modern global economy, those who have the means to produce energy are also able to exert other kinds of power – should they choose to do so – whether financial, industrial or strategically political. In such an unpredictable environment, the case for considerably more nuanced policies able to deliver energy independence is indisputable. The discussion, however, too often revolves around subsidies rather than efficiencies. 

Having stated at the outset that almost every building type can now be formed from wood, it should be said that this is not necessarily the case for the engineered structures required by some forms of renewable power generation. Hydro dams, wave energy and offshore wind turbines are examples for which timber solutions have yet to appear – although operational wind turbine towers and blades made from engineered timber exist in Austria and Germany. This is not to say that they won’t – simply that the development finance required to take engineered timber, wood modification and timber/concrete hybrid technologies to the necessary advanced and scaled-up levels, especially with subsidies in the renewables sector being reduced or withdrawn completely, has yet to emerge. 

Biomass might be a more immediate thought when one considers the use of wood in the generation of energy but, in a circular economy, this is possibly the last option to contemplate for something that is, after all, a highly reusable natural resource. While infinitely better in terms of carbon emissions than its previous coal fired process, some 98% of the biomass required to feed the huge demands of the Drax power station, for example, comes from overseas – 73% from North America. Even allowing for it being sourced from sustainably managed forests and the fact that the carbon emissions associated with its transportation are relatively small, biomass is not perhaps the ‘silver bullet’ needed to deliver long-term energy independence, especially if rolled out more widely on a similar scale. 

Which leaves us with waste – power and heat generated from the detritus produced by consumer society and the types of buildings required to house the plant and equipment involved. In the past, these facilities have been constructed using steel frames, themselves recyclable, and cladding and have hardly been objects of great beauty, but a new breed has begun to emerge. 

Making use of waste

Consumer waste is indeed one of the challenges of our times, and one that requires local solutions. Many would argue that we should focus our endeavours on encouraging people to reduce the amount of waste they produce. The hard reality is that it will take considerable time before the public willingly reduces its consumption and fully engages in the recycling options available – and until doing so there will be an ongoing need to dispose of massive quantities of domestic rubbish. Black bin waste that goes to landfill currently costs taxpayers almost £85 per tonne in Landfill Tax and so, for local authorities, it is imperative to find other solutions such as energy and waste plants, of which there are now quite a number around the country.

What singles out the new Recycling and Energy Recovery Facility (RERF) in Leeds, UK, is that it is the first energy recovery centre to feature a recycling element before the rubbish is processed into energy. It was designed by Jean-Robert Mazaud of S’pace Architectures, France, who has specialised in this particular building type for more than 20 years – he has delivered at least five other energy and waste management facilities in the UK, as well as many more throughout France. Its distinctive physical form lies in the engineering and materials used in its construction – a series of arched, engineered timber frames that stand 42m tall. These have been formed by Hess Timber, Germany, one of Europe’s leading manufacturers of glulam timber, from sustainably sourced European larch. When manufactured, as here, into a large scale engineered timber product, it can deliver a structural solution distinctly different from the heavy materials traditionally used for this type of facility. Adding to this unusual characteristic is the extensive green ‘living’ wall of its 125m-long south façade, which is one of the largest in Europe. This not only enhances the visual impact of the building but also contributes to its biodiversity, a feature that helps fulfil Leeds City Council’s brief that the facility should not only provide a landmark in the Aire Valley but that it should visually communicate its sustainability credentials. 

When fully operational, the RERF will process up to 214,000 tonnes of the city’s annual black bin waste – around 75% of Leeds’ total bin output – and up to 75% of the total waste that will be brought to the site, the remainder being made up of commercial waste. Recyclable materials will be harvested and the remainder incinerated. The combustion process is anticipated to generate 11 megawatts of electricity, which will be fed into the National Grid. Also in development is a district heating scheme designed to pipe heat from the steam created in the incineration processes to municipal buildings, swimming pools, libraries and high-rise council flats. 

Overall, it is anticipated that the 25-year, PFI-funded project will save taxpayers more than £200m in Landfill Tax and environmental levies. The facility is a key element in this particular local authority’s long-term waste and recycling strategy. To help the city break through the 60% barrier for overall recycling rates within the next few years, the RERF has a visitor facility to give people the opportunity to learn more about how it works and what they can do to contribute to better waste management and recycling in Leeds. Other sustainability elements, such as rainwater harvesting and drainage techniques, integrated throughout the design only add to the characteristics that distinguish this building from the more prosaic industrial facilities normally associated with the waste processing. 

Some measure of the design and construction achievement can be appreciated by the fact that the facility won the title of ‘Project of the Year’ in the 2015 Structural Timber Awards – no mean feat for a building type never previously associated with the use of wood and one which has opened many eyes to the materials potential. 

As a valuable contribution to the UK’s energy mix, the RERF has many characteristics replicable in other conurbations and, with its use of timber as a primary structural material, is a positive contributor to the environment. In confronting the domestic waste challenge we may finally be developing viable and locally sustainable – timber – solutions.

Peter Wilson is an architect and managing director of Timber Design Initiatives Ltd. The company works to deliver new, Europe-wide approaches to education, innovation and demonstration of best practice in the use of wood in architecture, design and construction through applied research collaborations between academia and industry.