Delivering Large-Scale Low-Carbon Buildings
Christian Dimbleby, Associate, Architype, explains how timber is increasingly being used in education buildings to create low-carbon and healthy spaces for staff and students.
At a time when climate change is at a critical level, the construction industry is faced with intense speculation as to its approach when reducing environmental impact in new buildings. It is essential that architects and others involved in designing the built environment tackle this challenge head on. When it comes to ensuring net zero carbon buildings, timber plays a key role.
What do we mean when we say low-carbon design or 'net zero carbon buildings'? The UK Green Building Council splits the definition up into two sections – construction and operational energy. This is an important distinction, as currently UK Building Regulations only focus on operational energy through Part L requirements, which themselves are nowhere near stringent enough.
Although approximately 28% of global carbon dioxide emissions come from building operations, a further 11% comes from building material and construction often referred to as 'embodied carbon' or, as a recent trend has defined it, 'upfront emissions'. When you look at the impact of new construction over the next 30 years to 2050, the role of building materials is significantly more important than building operations by up to nine times the emissions.
Timber is a low-carbon material: it is a natural product, needs minimal processing and refinement to make into a usable building material, and can lock up carbon in the building through 'carbon sequestration' – which is why it is sometimes thought of as carbon negative. But, even if this last aspect is not accounted for, timber still has significantly lower embodied carbon than alternative building materials, such as concrete, steel, brick or blockwork.
At Architype we have developed a detailing strategy using timber to ensure that building designs achieve the highest thermal performance on education projects. The system uses deep timber I-joists or Larsen trusses on the outside of the timber frame or cross laminated timber (CLT) structure, which can then be filled with cellulose (recycled newspaper) to form an envelope with no thermal bridges and minimal temperature loss/gain through the envelope. These requirements reduce heating demand by 90% compared to typical newbuild schools and help to meet the Passivhaus standard, which ultimately aims to minimise operational energy.
Timber also has many other environmental benefits besides lowering carbon. The research into biophilia has shown that being surrounded by nature can benefit health and wellbeing. It can provide great aesthetics and being surrounded by the beauty of nature and natural materials puts us at ease, lowering stress levels and other wellbeing indictors. This is essential in educational buildings, where lower stress and being at ease assists in retention of information and learning.
CLT has a higher strength to weight ratio than solid concrete. Moreover, one cubic metre of concrete weighs approximately 2.7 tonnes, while one cubic metre of CLT weighs 400kg. Reducing the weight of the superstructure means that foundations can be significantly reduced, which saves both money and carbon. Architype's timber educational buildings generally have no piled foundations; they can be installed on a minimal concrete raft, with insulated formwork. Similarly, the lightweight nature of timber means that it is possible to expand existing facilities without adding new foundations, such as the rooftop extension at The Gower School, a Montessori school in London.
Flexibility is a critical part of a functioning circular economy, as this allows buildings to be reused and adapted by others over time, rather than being used for a single purpose and then discarded. Careful spatial planning combined with modern timber structural solutions that can easily span 6m to 8m allow this. Timber is advantageous as it is the best material for simple adaptation on-site – cutting holes and adjusting is much simpler and easier than with steel or concrete.
Where possible, locally sourced materials should take priority, as this substantially reduces emissions from transportation, as well as increasing sustainable employment in the local area. For the Enterprise Centre at The University of East Anglia, a materials map was devised at competition stage to evaluate what local products could be used. In the end 80% of the structural timber frame came from Thetford Forest, and the columns to the front were larch from the Brandon Estate, Suffolk. The cladding was Yeoman wheat straw thatch, grown and harvested locally, and the clerestory roofs were clad in Norfolk reed.
Similarly, in the design for Burry Port School in Carmarthenshire, the timber came from locally sourced forests. The timber frame consisted of Welsh/borders larch: the Brettstapel was sourced largely from Welsh woodland, 90% Sitka spruce and 10% Douglas fir. Beech was specified for the hardwood dowels and cladding from untreated Welsh/UK-grown larch.
Many redundant materials were also reused in the construction of the Enterprise Centre at the University of East Anglia. The timber cladding on the west facade was made from old Iroko laboratory desks that had been sitting in storage for many years and were simply cut and planed to form a beautiful facade. Coppiced timber screens that had been used in the Sensing Spaces: Architecture Reimagined exhibition at the Royal Academy of Arts in 2014 were repurposed into dividing screens in the open space ground floor. Spare furniture was used, rather than building new – this included the reception desk from the Sainsbury Centre for Visual Arts at University of East Anglia (as due to popularity a larger one was needed), as well as most of the seating and furniture in the upstairs pods.
The Government has promised funding for school refurbishments and to create one million new school places by 2020. The operational and embodied carbon of buildings can be radically reduced through the use of timber, without impacting on the design quality of the building. Future building design will have a choice between designing from materials, such as timber, that allow the building to be grown consuming mainly sunlight and the carbon that we are trying to limit, or materials that require unsustainable and often irreversible damage to the Earth's natural capital.
www.architype.co.uk
This is an extract from TRADA's Timber 2020 Industry Yearbook. To read the full article, with supporting references and further reading visit: www.trada.co.uk
Read Structural Timber Magazine- Issue 26 here
