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Carpenter Oak & Woodland built the enormous new oak roof above the Great Hall at the Castle. The roof is 150 ft long and 50 ft wide and towers 50 ft above the 16th century hall. It features 57 Hammerbeam Trusses and comprises 6 articulated lorry loads of green (unseasoned) oak. The work was carried out on behalf of Historic Scotland (the Scottish equivalent of English Heritage).

Prior to the event, the pair received a request from the Queen's staff that they be presented to Her Royal Highness to explain the work involved in building this vast oak frame. They were thrilled to receive such an honor, and commented on her understanding of the construction process: "Her Royal Highness certainly has a good working knowledge of building and asked some extremely pertinent questions." Furthermore, Prince Philip, who accompanied the Queen, recognized the company's name and commented, "Oh, it's you again, you were at Windsor."

The firm, recently won an award for its craftsmanship in the repair of the Medieval kitchen roof at Windsor Castle. Carpenter Oak & Woodland specializes in the restoration of mediaeval timber frames and the production of new, green oak timber frames. The company was established in Wiltshire in 1987 and now operates from yards in Chippenham, Devon, Oxford and Scotland.

New Roof at Stirling Castle

The Army turned the Great Hall into Barracks in the 18th century. In those times, not having any regard for the history of the building, the Army inserted floors and walls, blocked the original windows, inserted smaller new ones, in keeping with its new function, added chimneys and dormers, and re-built the gables.

As a result of this thorough re-modeling, there was little or no evidence to suggest what was there originally. Thinking has moved from Restoration to Conservation, and were the decision being made today, it could be argued that the outcome would have been to conserve it as it was when the Army moved out. This meant that the taking-down work to remove the alterations was doubly important. Not only was there a need to pinpoint any evidence that would identify the original form of the building, but also to record information about the army works to add to the general fund of information about building work of that period.

The key piece of information relating to the Stirling Great Hall roof was the Board of Ordinance survey of 1719, as this was carried out not long after their survey of the Great Hall at Edinburgh. By a careful examination and survey of the Edinburgh roof, which is very similar, although smaller, and has remained largely intact, (discounting the Victorian repairs), they were able to produce drawings and jointing details for the Stirling roof.

Carpenter Oak & Woodland became involved with this project in early 1996, as a result of meeting the Historic Scotland team at the Institute of Advanced Architectural Studies in York. Carpenter Oak & Woodland were demonstrating practical conservation techniques, and their enthusiasm for the Castle project led the Stirling team to add Timber Framers from south of the border to the tender list.

Having been successful with their tender (at a third the figure of two other tenderers), Carpenter Oak began work in November 1996. They started with a full measured survey of the wall heads of the Great Hall, and relating this to the stubs of the original corbels for the principal posts to the main Hammerbeams. These corbels had been discovered during the down-taking works. At the same time the roof at Edinburgh was closely examined to check the jointing and for pointers as to how the roof had been laid out.

Over the two preceding winters, Historic Scotland had procured and had cut all the timber for the roof; the timber had to be inspected, shipped to Wiltshire, and be re-graded according to its final use.

Because the west wall of the Great Hall (which has very large/tall window openings, and many Chimneys) had deflected outwards as a result of the thrust from the original roof, the wall head had a significant curve. Part of Carpenter Oak & Woodland's contract was to cast in situ 400 mm by 400mm reinforced concrete beams; these beams were linked by high spec nitronic stainless steel tie rods (with strain gauges linked to a computer monitoring system). The brief was to build the new roof such that the ridge was both level and straight. The result that every truss had a slightly differing pitch and span. To add to the complexity, the corbels' positions varied to such a degree both along the wall, and with their opposite across the hall, that the positions of the principal trusses were set such that none of the fifteen bays had the same distance between them, and none of the trusses were parallel with each other.

In order to build this flat on the ground some 400 miles south of the site meant that a special computer spreadsheet had to be written to fix the setting out in three dimensions (and at the same time the data was manually checked to ensure no errors).

There were slight changes made as a result of the surveys, and in light of experience of other similar projects, some of the proposed joints were modified.

The laying out and cutting of the joints was started in late November 1996, and continued until the end of April 1996, using traditional scribing techniques. By this time approximately 150 tons of timber had passed through the Wiltshire Yard, all either mortise and tenoned, or scarf jointed to be fixed with hand drawn pegs.

The hardest part of the project, the erection on site, started in mid-May. The timber was shipped back to Historic Scotland's central stores depot in Stirling on six articulated lorries, cleaned and carefully sorted into the exact sequence of erection. Special trolleys were fabricated to manoeuvre the timbers, some of which were over 26 feet long, and a half ton in weight.

The two main problems were to provide safe access for the teams erecting the trusses, and the challenge of getting the timber into the roof space. The top of the Great Hall had been totally enclosed by a large and impressive temporary structure. As the castle sits high above the town on an exposed rock, the engineering and construction of the temporary enclosure is a masterwork in its own right. The design allowed for five crane rails / runway beams to be rigged running along the entire length. These beams carried trolleys from which chain blocks, electric hoists, and fall arrestors were hung. A significant disadvantage was the necessity to have two sets of scaffolding to support the temporary roof, running continuously the length of the Great Hall, 1.5M inside the wall heads. Because of the risks the team assembled to work at the Castle included two experienced Canadian rock climbers (who also happen to be timberframe builders), and locally recruited steel erectors.

The timbers were transported on a specially modified truck, four tons at a time, carefully scheduled so as to avoid the times when the Castle was open to the public, and hoisted four stories onto the exterior loading platform. A team on the platform wearing fall arrestors and safety harnesses transferred the half-ton packs onto trolleys, through a window, and via the interior lower platform, hoisted through a hatch, up into the main working deck.

All the trusses had to be assembled piecemeal, threading their component pieces through the interior scaffold lattice, slinging from hoist to hoist, until they could be temporarily propped into place while the rest of the frame was assembled.

To get the work done to meet the programme, a high degree of coordination and site management was required. The erection team, despite working a 12-hour day, had to be on the ball at all times, especially during the frantic sessions at the beginning and end of each day required to get the timber in. The ban on access for vehicles delivering timber from 9:30am to 6:30pm, (opening hours) meant that timber had to be cleaned, delivered, transported, and hoisted, in the exact sequence in which it was required. Any snags would have meant the entire crew standing idle.

The final phase of work (and the final commissioning and calibration of the tie rods) was the fixing of 700 m2 of 25mm random width oak sarking, which was carried out in the last two weeks, completing in July 3, weeks earlier than scheduled.

Wiltshire company Carpenter Oak & Woodland, Ltd., has won an award for its craftsmanship in the repair of the medieval kitchen roof at Windsor Castle. The Special Award was made by the Worshipful Company of Carpenters within its Carpenters Awards 1999 - a biennial award scheme, now in its 29th year.