The UK currently imports 82% of all wood used and this has a negative effect on UK forestry, with only 59% of our woodlands in active forest management. Of the hardwood we harvest in the UK, 76% is burnt as fuel.

Noble species including oak, ash, beech and sweet chestnut have been used throughout the UK for construction because the timber provides excellent mechanical strength, stiffness and, when detailed correctly, long lasting durability. The onus is on designers and suppliers of UK-grown timber to demonstrate value-added uses for these excellent materials and well before the point at which it’s burnt for energy.

As demonstrated by a number of landmark buildings in the UK, it is possible to promote a culture of ‘local materials first’ that can ensure elevated use of the UK’s diverse timber resources whilst bringing many positive changes to society:

  • sustainable growth of rural economies through widespread forestry, processing and distribution;
  • greater bio-diversity in our woodlands through active forest management and a higher amenity value associated with our woodlands;
  • much needed afforestation of the UK as part of a sustainable economy;
  • low embodied energy, high carbon storage timber buildings that are better for our physical and mental well-being.

To test the validity of these ideas and to act as a case study for positive change, our students at the Cass school of architecture experimented with hand-cleft sweet chestnut, exploring how this species might be ‘specified-in’ to the built environment through a creative design process.

As part of a four-day making workshop, the students prototyped, tested and built a range of spatial timber structures using a hybrid combination of graded imported and un-graded domestically grown timber. Chords of trusses were of imported softwood and the connecting web members of local cleft sweet chestnut. The resulting structures were lightweight, fast to make, cheap, structurally viable, and made, in part, from materials grown one hour from the building site.

Sweet chestnut was chosen as an underused, durable timber with a high degree of naturally occurring anti-fungal extractives. When coppiced as part of a well managed woodland, ‘stools’ of multiple stems of straight growth are promoted and harvest cycles can be two to three times higher than that of other fast growing UK tree species such as Sitka spruce, depending on the diameter of roundwood required. Once harvested, chestnut stools naturally regenerate, unlike clear-felled or extracted trees, which require re-planting. This cycle of growth and harvest can repeat indefinitely with some of the oldest trees in the UK, coppice stools.

Once de-barked, harvested sweet chestnut roundwood exhibits very little sapwood and when hand-cleft into the small diameter lengths that we used for our workshop, is a zero-waste process. Cleaving the timbers apart also leaves the wood’s cellular structure largely intact, making for a more durable timber surface.

Cleaved wood also taps into existing rural industries such as the flourishing supply chain in sweet chestnut fencing. This is an example of a sustainable, growth industry that provides, local, healthy, well-paid and highly skilled rural jobs that are good for local biodiversity. Coppicing can also contribute towards the mitigation of climate change. Recent studies in Europe have found that coppicing practices with sweet chestnut can increase the volume and rate of sequestered carbon from the atmosphere whilst simultaneously providing viable timber for long-term applications like construction.

To ensure though that ‘non-standard’ timber is readily available on the market and safe to use as part of a building structure, we need grading standards that are better representative of the full range of characteristic properties that abound between timber species and even between trees of the same species grown in different conditions.

In some cases this may mean batch assessing local timber in a non-harmonised manner. In our application of sweet chestnut as web members spanning between chords of a truss, this would mean identifying upper and lower longitudinal density ranges for these components so that a structural engineer can be confident of the mean structural properties of each truss and apply a suitable factor of safety to their calculations.

Whilst ‘non-standard’ this is well within the capabilities of the industry, as demonstrated by a range of innovative buildings made using local timber in the UK including; the UEA Enterprise Centre, the Flimwell Wood Enterprise Centre or the woodland campus buildings of Hooke Park in Dorset.

Let’s not forget too that there are many thousands of medieval timber buildings still standing safely in the UK made from local material that were built using nothing more than an intuitive understanding of wood and an intelligent use of its properties.

Extracts from the piece are under review for publication by the International Wood Products Journal.