In this exclusive extract from Timber in contemporary architecture: a designer's guide by Peter Ross, Giles Downes and Andrew Lawrence, we analyze the enduring appeal of timber.
Timber is a material with a unique charisma – it was, after all, once living, and its organic origins are clear in its appearance and texture. It also has an historic resonance, since a thousand-year tradition is still evident in the great frames and roofs of the medieval period and earlier. Overall, its appeal to designers is based principally on its:
- Visual and tactile qualities
- Material properties
- Environmental credentials.
Visual and tactile qualities
The appearance of timber, in terms of its colour range and surface texture, is probably the primary reason for its use in both carpentry and joinery. The colour can vary from the light cream of birch, to the regal depths of African walnut, with many intermediate shades.
But the appeal lies not in the colour alone (since any particular shade can be replicated with paint) but in the organic lines of the surface figure, created as the geometric plane of the saw-cut intersects the naturally formed growth rings of the trunk. The figure may be further enlivened by knots, which of course mark the branch positions on the original truck. Thus, strictly, each piece can be considered unique. It is these inherent small variations between planks which give a liveliness to the surface of an assembly, such as panelling or cladding.
The long traditions of the carpenter and joiner testify that timber is the most easily worked of the construction materials, and that its appearance can also be influenced by the method of conversion from the log. At its simplest, cleft timber is formed by splitting the log with a blade which follows the grain, a technique most often used for fence rails. The results are rarely straight, but form members which are exceptionally strong and resilient. The use of an adze results in a surface with shallow scallop-like depressions.
Band sawing produces a characteristic marking on the face, while fine sawing is only discernible on close inspection. All conversion marks can be removed by planing, which nevertheless shows the figure most clearly, and is the most user-friendly surface in areas of frequent hand contact. Wood is also an excellent medium for carving although, unlike free-stone, the material has a grain, and the carver must respect this.
While the most charismatic species are largely confined by their price to joinery work, there are many softwood timbers which have handsome and distinctive figures.
The properties of timber can be traced back to its organic origin. Its cellular structure is strongly directional, which in turn generates linear members with a strength-to-weight ratio exceeding that of mild steel, and makes timber very appropriate for roof construction. The restriction which in the past limited individual members to the size of cut logs has been removed by the development of durable adhesives which allow individual laminates to be glued together, until their size is limited only by the constraints of transport.
A vocabulary of connections between the members themselves has evolved, from traditional all-timber interlocks to modern fasteners of metal. Although the cellular structure of the material imposes a discipline on the design of the joint, the procedure is set out in modern design standards. There is also a visual satisfaction in seeing the logic of construction expressed in an assembled structure. No other building material has such a historic breadth of structural vocabulary, which can be seen across the world from Europe to the Far East.
Combustibility, and the possibility of fungal decay, are sometimes seen as the downside of timber construction. Originating from the organic nature of timber, they are in reality issues of design which have established solutions in terms, for instance, of applied protection for fire resistance, or species choice in relation to durability. For much routine design work, these issues require no special consideration – roofs normally need no period of fire resistance, and all species can be regarded as durable within the weather envelope of the building.
Unprotected timber on the external face of the building also undergoes a colour change, but this should be regarded as a material characteristic, rather than a defect, which for well-detailed assemblies can enhance the appearance.
In little more than a generation, concerns relating to the environment, such as the greenhouse effect and the finite nature of our resources in relation to a burgeoning world population, have moved from an unthought idea, to discussion and debate, and then (in many cases) to legislation which attempts to limit the consequences of global warming.
Timber, in these terms, is a very 'green' material. If forests were suitably husbanded, supplies could be maintained indefinitely for minimal carbon emissions, and the purpose of the various certification schemes is to ensure this.
Currently, the world's softwood forests are actually increasing in area. Thus timber has the lowest carbon emissions, forest-to-site, of the major building materials. In addition, timber in a building effectively sequesters carbon, rather than releasing it to the atmosphere. For these reasons, timber scores highly in the various environmental assessments now required for any new building.
Find out more
Written by leading specialists in timber architecture and engineering, Timber in contemporary architecture investigates materials, connections, applications, and celebrates innovation. Excellence in timber design is demonstrated in the last section of the book which is devoted to seventeen highly illustrated case studies, some award-winning, some groundbreaking. All of these have been chosen for their inspirational qualities, and include: Visitor Centres at Savill Garden and Alnwick, Weald and Downland Museum, David Douglas Pavilion, Mossbourne Academy, Formby Pool, Kingsdale School, Haberdashers Hall, Ealing Bridge, The Globe Theatre, Carlisle Lane apartments, Sage concert hall.
Timber is a flexible and aesthetically appealing material that allows designers to develop creative, high quality, innovative and robust solutions to meet client needs and exceed their aspirations.
There are now excellent examples of timber being used for landmark buildings such as the award- winning Savill Garden Visitor Centre in Windsor Great Park, in the 9-storey Murray Grove residential building, in schools and wide span structures such as supermarkets and sports centres, and in both affordable and bespoke housing. Progress and transparency in responsible sourcing means that timber is frequently preferred for its low environmental impact.
Published by TRADA in association with RIBA Publishing. Copyright TRADA Technology September 2009.