A brief history of the arboretum
The arboretum was founded in 1829 by Robert Stayner Holford, whose family owned the large estate centred on Westonbirt House.
Using a family fortune, based on the supply of water to London, Holford financed and oversaw a huge planting programme, which hinged on the work of some of the Victorian age’s leading botanists.
He had the arboretum landscaped in the ‘picturesque’ style made popular by the eminent garden creator William Gilpin.
In 1875, Robert’s son Sir George Holford took over the arboretum project and much of the collection as it exists today is due to his vigour in pursuing the project.
In 1956, the arboretum was bequeathed to the Forestry Commission who have continued to improve and expand on the work of the Holford family.
The arboretum and Downs landscape is designated a Grade I Registered Park and Garden by English Heritage.
The Friends of Westonbirt Arboretum
In 1985, a small group of enthusiasts who saw the need to work with the Forestry Commission to preserve and enlarge this unique landscape met for the first time.
This group became the Friends of Westonbirt Arboretum and today we have more than 27,000 members – all helping to maintain the 600-acre site, with its 18,000 individual trees and shrubs.
Building the Great Oak Hall
Inspired by the construction of a small cruck barn on the Forestry Commission’s land at Leigh Woods, near Bristol, a working group of the Friends of Westonbirt Arboretum met in February 1998 to investigate the possibility of constructing a similar timber frame building in the arboretum.
The project was launched on 7th May 1999. The hall was built with funding from the Friends, together with generous outside help, as a gift to the arboretum.
The building was designed by Roderick James Architects and in particular by Rhys Brookes.
The idea for the entrance canopy came from a stone shelter at Mells in Somerset designed by Lutyens.
The timber frame was constructed from green oak using 40 large trees donated by the owners of local private estates, together with 60 oaks given by the Forestry Commission from the thinning of Silk Wood at Westonbirt.
The building was opened by His Royal Highness, the Prince of Wales on 10th November 2000.
The timber frame
During June of 1999 teams of volunteers, under the tuition of Henry Russell and Gudrun Leitz, fashioned nearly half the timber frame. The remaining was constructed by a team of carpenters during July and erected in August of that year.
Using traditional methods which have changed little since Mediaeval times, the frame was constructed from fresh felled, locally grown ‘green’ oak.
It was prefabricated in the framing yard, using only hand tools, the main beams having been pre-cut to size using a mobile band saw rather than the more laborious pit saw of earlier times.
The frame members were then assembled horizontally on the ground to ensure that all the parts fitted as specified. Each piece of the frame has its own name.
A Millers Falls drill, a device made in 19th Century America, was used to cut the mortices and peg holes. This ensured that the holes were vertical.
There are six trusses in the frame of the Great Oak Hall, two of which are of cruck construction having a curved member rising from the sole plate up to the collar.
The pair of crucks in each of the trusses has been cut from a single tree, the stem of which was suitably curved as it grew in the wood.
Each truss was numbered with Roman numerals on the upper surface when the frame was flat in the framing yard.
The carpenter’s marks are curved on the left hand side (looking from the entrance to the hall) and straight on the right hand side.
These numbers were marked on all the members of a truss, ensuring that they could be reassembled exactly as constructed in the yard.
The roof is a combination of old and new methods of construction.
The tiles are wooden shingles cut from Western Red Cedar (Thuja plicata) from the Dowdeswell Estate in Gloucestershire.
These are secured to treated softwood battens with copper nails.
The battens hold in place the ‘Corovin’ breathable membrane below which is ground rock wool to provide insulation.
The inner lining of the roof is a layer of thatch of wheat straw, held in place by chestnut laths and reflects similar Mediaeval structures such as the tithe barn at Englishcombe, near Bath and the Manor House at Lytes Cary, near Yeovil in Somerset.
The stone flags were cut from Cotswold limestone at Stanley’s Quarry, Upton Wold, near Moreton-in-March.
They are laid over plastic piping carrying water heated by a liquid petroleum gas boiler, which one might say is the modern version of the Romans’ hypocaust under-floor heating.
The entrance doors and those leading into the hall were made from English Oak by Sabrina Traditional Oak Doors of Shrewsbury.
The remaining oak doors were made by Jim Dean of Hereford. The design of the glass doors was etched by James Witchell of Overton in Gloucestershire.
The fitting out
Once the frame was raised on site, followed by a traditional ‘topping out’ ceremony, the roof and the internal fitting out was undertaken by Jim Dean, the main contractor.
The timber frame is made from green oak.
Seasoned oak is not only much harder to work with hand tools, but the fresh felled oak dries out in situ and as a consequence tightens the pegged joints.
Because movement of the frame occurs as the timber dries out, a special system of glazing was devised to accommodate this problem, avoiding breaking either the seal or the glass.
The oak pegs were cut by hand on a horse using a drawknife.