(a) Nave roof
Felling dates: Winter 1246/7 to Winter 1249/50
(b) South transept roof
Felling dates :Spring 1306 to Spring 1318
Construction of the present cathedral started in the late eleventh century, and was completed by the 1120s. During major repairs to the high roof of the south transept, the opportunity arose to undertake a detailed dendro survey. The investigation was also extended to the medieval portion of the nave roof. The nave roof timbers date from 1249/50 but the structure was reconstructed, perhaps at the time of Wykeham's remodelling of the nave in c.1400, or possibly after a fire in 1698 when the western five bays were totally replaced. However, the present form of the nave roof probably closely reflects its original form. It comprises a series of rafter couples with double wall plates, ashlars, soulaces, and double collars with a king strut between them. Every fifth couple incorporates a tiebeam connecting the inner and outer plates. At the time of the reconstruction, a system of queen struts and braced arcade plates was inserted to provide longitudinal bracing. The roof was hitherto thought to have dated from the time of Wykeham’s rebuilding of the vaults, but the dendro dates show that the stonework must have been inserted under the existing roof.
The high roof of the south transept is of very similar design to the nave roof, except that it includes four intermediate tiebeam trusses with queen struts to the lower collar. Both the nave trusses as well as the south transept roofs used mortice and tenon joints throughout. The samples have given precise felling dates mainly from 1316 and 1317, although one rafter dated to 1318, suggesting the roof was actually erected in that year. A re-used inner wall plate on the south-west side of the roof, thought to be of Norman date, has a latest ring of 1270, giving a terminus post quem or ‘felled after’ date of 1279. Thus it was probably part of the 1318 work. Another possible Norman element is a half-round timber column, or respond, fixed to the inside south gable below the southernmost truss. However, the crispness of the mouldings suggests that it relates to the inserted ceiling of 1820.