With the growing popularity of timber, there is a place for Welsh wood in construction
Design & Technical winner
Steven Coombs
The development of the building envelope using Welsh-grown timber
Welsh School of Architecture, Cardiff University
The UK wood revival of the last 30 years owes a lot to the influence of the unbroken tradition of timber construction in Scandinavia, the Alpine countries, Japan and North America. The publication of the work of architects such as Burkhalter and Sumi, Gion Caminada, Hermann Kaufmann and Peter Zumthor, who reclaimed their regional culture through the use of new wood building techniques, is now inspiring architects in other European countries. In the Graubünden, Switzerland, and the State of Vorarlberg, Austria, designing and manufacturing with timber has cultural connections linking back to material, craft, sustainability, architecture and ‘way of life’.
Use of Welsh-grown timber in the external building envelope remains minimal compared to the volume of imported softwoods and timber products. Experiences of the use of UK-grown timber are often based on negative perceptions related to poor timber properties, sourcing, limited skills and access to innovative technology and products. However, it is possible to use home-grown timber in the sustainable building envelope.
Wales has roughly 306,000ha of woodland, covering 15% of the total land area – considerably lower than Europe (45% average), Japan (69%), North America (34% average). As a result the construction industry in Wales relies heavily on imports, with many considering the crop to have limited commercial value and use. But Welsh-grown timber production is stable, and meets demand in markets such as pulp and wood fibre for paper, wood-based panels, pallets and fuel.
With forest cover and production likely to remain significantly below self-sufficiency levels for many years, if the use of Welsh-grown timber in the sustainable building envelope is to rise, there must be fundamental change to the local industry.
Pre-empting this, the Design Research Unit Wales at the Welsh School of Architecture at Cardiff University spent 15 years, in collaboration with the timber industry, exploring the use of Welsh-grown timber through a diverse range of prototype projects in the design and construction of building envelopes with a clear tectonic language. Projects focussed on its use in structures, external finishes and joinery and led to the following key observations.
The crop
UK silviculture has been dominated by mono-species coniferous plantations and clear felling. In recent years, woodland organization Coed Cymru and others have promoted continuous cover forestry methods, with dispersed selective felling and thinning, allowing woodlands to regenerate naturally. The remaining straight trees are left to keep growing, thus developing a mature growth forest and a supply of hi-grade, large section, quality timber for future generations. As this approach is adopted more widely, the output from woodlands is more likely to be high-yield softwood species generally limited to a C16 strength grade class and supplied in standard lengths and section sizes from large sawmills; and small sections and lengths of hardwoods (max. 150mm by 150mm by 1200mm).
Timber industry
Further reflections on the prototype projects provided the following observations on the woodland, crop and processing industry. Many species of Welsh-grown soft and hardwoods are appropriate for use, providing that their properties are understood and respected in the design. The industry is often willing to consider innovation by other means. Low-tech construction methods can be used in small local workshops, reducing risk and upfront costs. To improve the structural performance, durability and stability characteristics of the crop, low-tech engineered components can be modified. But, crucially, the industry lacks a ‘centre of excellence’ to provide advice and showcase research and development – which is essential for knowledge transfer, from forester to end user.
Function and design
The small and standardised timber sizes, based on 300mm and 600mm dimensional co-ordination, are best used within identified rules, grids and systems for structures and compositions of 1,200mm, 2,400mm, 3,600mm etc. The grids provide clear ordering, structural and/or constructional control and design logic that are integral to the use of timber, avoiding unnecessary complex details, form and material wastage. This co-ordination of timber properties, design and performance may be best expressed as elemental, modular and layered approaches to manufacture and construction.
This offers potential for the development of an architectural language specific to the use of Welsh-grown timber.
An additive timber tectonic
The design of standardised, prefabricated timber systems based on repeating species, components, elements and spaces draws inspiration from Jørn Utzon’s notion of additive architecture: ‘A consistent exploitation of industrially produced building elements is only achieved when these elements can be added to buildings without the components in any way needing to be cut or adapted.’
The development of a Welsh-grown timber industry is best based on standard lengths and section sizes either determined by sustainable woodland management and sawmill processes. These will form the base timber components from which all products and elements can be manufactured. These lengths and sections as supplied or in exact divisions or multiples of standard lengths, can be used to maintain material efficiency. This, in turn, influences the sizes of elements, panels and volumes to be composed into modular units. The result is a tectonic expression unique to Welsh-grown timber but flexible enough to allow for material expression and a contextual response.
Five steps in additive working
Five aspects of an additive principle have been identified from woodland to architecture. The principle operates both as a bottom-up approach to timber use and fabrication and a top-down expression of Welsh-grown timber in the building envelope, generating an indigenous, tectonic timber architecture.
The species: Woodland management and the extraction of small-medium diameter roundwood of all species for processing provides the limiting factor dictating to the industry.
Sawnwood, veneer and waste: The reduction of roundwood into standardised sizes is determined by the needs of the construction industry and an efficient exploitation of roundwood that form the basic components or modules.
Engineered components: These come from multiple short lengths and small sections to manufacture rational, planar and rectilinear products. This additive approach suggests the engineering of all timber through layering, cross-layering, sandwiching, finger-jointing and orienting to enhance the performance of the basic sawnwood, veneers, chips, strands and sawdust.
The building element: Sawnwood, engineered timber and timber products are incorporated into a range of modular and/or prefabricated building envelope elements.
The tectonic module: These may be elemental, panelised, volumetric or a hybrid combination but are repeated in logical grids to provide structure, enclosure, finishes and define space. The resultant tectonic is honest to the use of Welsh-grown timber to provide an efficient, low-energy building envelope. Space, composition, form and timber materiality are all expressed and respected as a tectonic timber architecture.