Timber has been used for thousands of years as a building material and it is increasingly important as the challenges of low carbon building develop further. In Britain we have a long tradition of timber use from the beautiful timber framed buildings of the Tudor period to the magnificent beams in our ancient churches, along with agricultural use, shipbuilding and furniture production.

Of course, timber has also always been used as fuel, both as logs and charcoal. Although iron and other materials have replaced timber in shipbuilding, it is still used extensively for construction and furniture.

Much of our timber is felled under the UK Woodland Assurance Standard, which is currently the central component of the forest certification programmes operated in the UK by the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification Programmes (PEFC).

In 2010 it is estimated that just over 10 million green tonnes of timber were extracted from UK forests. Of this, 95% was from conifers yielding softwood timber and just over 500,000 tonnes were from broadleaved trees giving hardwood timber. Just over half of the softwood volume and the majority of the hardwood were from private forestry enterprises and the rest from Forestry Commission forests.

Forest products exports
This harvested timber is feedstock for a number of industries, with 59% of the material going into sawmills. However, 15% is used as fuel wood and 11% is used by the UK panel board industry. The remainder goes to the pulp and paper industries, for production of fencing as well as other uses. Although a net importer, we do export £1.8bn of timber and timber-based products – mostly pulp and panel boards.

Forestry and primary timber processing employed 41,000 people in 2008 when figures were last available, with many thousands more being employed in secondary wood processing and other wood-using industries. Construction is the largest market for timber in the UK and British-grown softwood is widely used both for structural and non-structural applications.

Softwood species
Softwoods are dominated by Sitka spruce. As well as being suited to paper pulp production due to its long, pale coloured fibres, Sitka spruce is used in production of pallets, general carcassing and panel products and it also provides a good quality structural timber. UK-based companies have invested in state-of-the-art machinery to produce large volumes of high quality, graded material. It is graded to BS EN 14081:2005 and production lines produce hundreds of thousands of cubic metres of C16 material every year. It is used wherever a structural grade of C16 is required – more often than may be thought. C24 is often over-specified in a sometimes-misguided assumption that it is better than C16. While it is indeed stronger, in many cases C16 will be sufficient. Indeed, with the advent of thicker stud sizes resulting from changes in the building regulations, C16 strength-graded material has an increasing role to play.

The second most abundant softwood in the UK is Scots pine and this also produces good quality machine-graded C16 structural timber, while visual grading can produce material to C20 and C24 strength classes with timbers as large as 450mm2x8m being available. It is also used for carcassing, with smaller diameter material being used for fencing. There is also a strong market for Scots pine cladding boards.

Although only amounting to about 10% of the volume of Sitka spruce, Douglas fir also provides structural
material. It is much favoured for its straight grain and superior stiffness and strength when compared with Scots pine. Douglas fir is available in large sections and is often used in green framing.

The Sears building in Golspie is made of Douglas fir structural timbers and Scots pine cladding Mark Williams, HRI Architects, Inverness, from Forestry Commission Scotland

Larch is a very popular timber for cladding and is abundant at the moment. Due to fungi-like pathogen Phytophthera ramorum, large volumes, particularly in the south-west, are being felled when the disease is found, or as a precaution. The Forestry Commission is working hard in its own forests and with private forestry owners to try to stop the spread of the disease. Timber from the affected trees is suitable for use and bio-security measures are in place to stop the spread from felled timber. As well as cladding, larch is used for fencing and can be graded to produce structural timber, although this is uncommon. Machine grading of larch to utilise the large volumes currently available is being investigated.

Other softwood species are also present, used in the UK’s strong panel board industry or for fencing and, of course, fuel. We also have small volumes of western red cedar, which is popular for use as cladding, although our faster grown material is sometimes knottier and will have a slightly different appearance to that imported from North America.

This is the case with many of our home-grown softwoods and sometimes durability differs from imported material. These factors, therefore, should be taken into account when specifying home-grown material for use externally. The book Sustainable Construction Timber published by Forestry Commission Scotland provides a valuable resource for advice on how to specify British-grown material.

Hardwood resource
The hardwood forest cover is dominated by oak with birch, ash, beech and sycamore being the other prevalent species and 30% of the hardwood forest cover is mixed species.

Oak is one of our favourite timbers. It is used in structural applications in green oak framing as well as decking. Oak’s durability means it can be used externally without preservation, such as in window frames and cladding. Care should be taken to ensure that it weathers evenly and tannin run-off that occurs as weathering takes place is considered. Another hardwood species often used for cladding is sweet chestnut, a moderately durable hardwood that is occasionally used for framing.

Due to their lower durability, ash, beech and sycamore are used for internal joinery, flooring and furniture. As part of its plans to increase the upland hardwood resource, Forestry Commission Scotland will use ash and sycamore to replant some softwood plantations and grants are available for this. Other more specialist hardwoods available are cherry and elm, both much valued for their appearance.

UK innovation
Innovation abounds in the British timber industry, with products such as the Coed Cymru Ty Unnos building system. Engineered I-joists are produced in the UK using British-produced OSB for the web and in, some cases, British-grown C16 timber flanges. Pilot work is being carried out to examine the feasibility of using British-grown timber for the production of glulam and cross-laminated timber.

The government sees the benefits of our timber resource as something that will help mitigate climate change as well as providing economic benefits to the UK. Many initiatives are in place to increase forest cover and clearly all of this will lead to an increase in resource in the future.

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