Donald Insall Associates was appointed to rectify water ingress threatening the ornate medieval stone carving in this Grade I listed Scheduled Monument partially built between 1295 and 1298, which was then completed in 1306 with some elements left unfinished. Remedial works involved taking up the existing cobbled roof finish under archaeological supervision and providing a new membrane isolating new works from medieval fabric. Sandstone flagging with a perimeter drainage channel was provided. New lead-lined spitters dispersed water away from the historic fabric and channelled it from the main roof into the outer ward below. The interior of the chapel was also re-floored using sandstone flags, with discreet up-lighters installed so as to emphasise the intricate medieval carving. The walls were lime-washed to encourage the fabric to dry out and discreet ventilation was introduced to the high-level roof light.