Summary

  • The Olivier Theatre at Bedales School is framed in large sections of green oak.
  • The majority of green oak projects use British-grown oak.
  • British-grown oak has many environmental advantages, particularly if sourced locally.

There has been a resurgence of interest in oak framing as the genuine structure for a wide range of buildings, from small residential to relatively large structures. The structural frame may or may not be exposed on the outside of the building, but the appeal lies largely in the scale and nature of the green oak framing internally. Traditionally, oak frames were exposed on most houses, whereas for barns, factories and warehouses they were concealed behind brick or timber cladding. Both techniques are now used in new buildings.

One example of the modern use of green oak framing is the Olivier Theatre at Bedales School, near Guildford in Surrey, by Feilden Clegg Bradley, built in 1993. This building has been framed in large sections of green oak using traditional carpentry joints and dowels for the smaller spans in the two-storey foyer area.

The architects were very aware of a particular feature of undried oak, which is that large sections will continue to shrink considerably even after the building is in use, because the sections are too large to be fully dried before they are installed. Detailing must therefore always allow for this movement and for any possible distortion of the wood that may occur during the in situ drying process. This requires considerable care, particularly when the green wood abuts other components such as glazing, masonry or conventional timber frame construction.

Globe Theatre

Perhaps the best known example of modern green oak construction using traditional carpentry joints, and with all the frame members exposed, is the Globe Theatre in London, designed by Peter McCurdy, to re-create the 16th century Shakespearean theatre. However, there are now many other examples of this type of construction in the UK, some traditional and others entirely contemporary in design.

There is also the common use of oak framing for repairing and converting old barns, or for large conservation/restoration projects, where historic buildings may have been damaged by fire or decay. The great roof of York Minster was repaired using substantial sections of oak, but on a smaller scale this is typical of the repair of many parish churches throughout the country.

In the majority of these projects British-grown oak has been used and, despite the huge loss of old oak forest, largely for shipbuilding up to the middle of the 19th century, there is now plenty of oak available from the regeneration and commercial planting that took place in the 18th and 19th centuries.

Building components

British-grown oak is also used for other building components such as windows and doors, cladding boards in various profiles, or external decking, whether associated with oak structural frames or not. Used green, these components need careful detailing to allow for the shrinkage and possible distortion of the wood – and, while using undried wood may save the cost of kiln drying, or the time required for air-drying, there may be extra costs in the fixings necessary to allow for such movement.

A particular feature of oak is the high quantity of tannin in the wood, which will exude slowly when exposed to sunlight and weathering. This will be most evident in green wood, and will gradually dissipate throughout the bleaching process.

British-grown oak has many environmental advantages. Individual trees can be removed from woodland, thereby maintaining the use and appearance of the setting. It is obviously renewable, and there is now much greater emphasis on replanting native hardwoods in the UK. Oak requires little energy in conversion or transport, if locally sourced. Its natural durability means that there is no need for preservatives or coatings, and consequently little maintenance. Finally, it can be reused in many ways after its original use has been finished, as shown by the frequent historical use of ship’s timbers and other oak components in building construction.

More case studies can be found in Green oak in construction, published by TRADA Technology Ltd, in partnership with the Forestry Commission and Scottish Enterprise. Visit www.trada.co.uk/bookshop for details.