Recently, as part of an extensive restoration project undertaken by Historic Scotland, the hammerbeam roof of the Great Hall at Stirling Castle was completely restored. Green oak from 350 Perthshire trees was used to fabricate and erect 57 hammerbeam trusses spanning approximately 15 metres. Since its construction around 1502 by King James IV of Scotland, structural loads from the roof had caused the walls of the hall to deflect outwards. To ensure that the ridge of the roof would be level and straight, the trusses were each made with a slightly different pitch and span. The restoration started in 1991 and was completed in 1999.