Despite an ongoing series of repairs the current copper roofing (distinctive for its green colouring) is no longer able to keep the Cathedral watertight. Consequently, rainwater is able to penetrate the roof vault, damaging the medieval timber roof structure. These leaks are also damaging the historic masonry and ceiling plasterwork. The roof also suffers from restricted air flow, which creates the ideal environment for further decay and wood-boring beetles.
Lighter than lead, the copper panels are lifted by coastal winds, allowing a fullness know as 'oil canning' to develop, causing the copper to crack and, at worst, to come away from their fixings. Copper becomes 'work hardened' and cracks are often impossible to repair, requiring hot work at very high temperatures which presents an unsuitable fire risk to underlying timber structures.
In an attempt to make the roof secure, panels were screwed down, however, these holding repairs have weathered, creating a sieve of slow leaks which endanger the historic fabric.
Recent inspections into the fabric of the building identified the Cathedral's roofs as a priority restoration project. The roof comprises the Quire (the central area), the Nave, and the North and South Transept roofs. The work cannot be delayed without risk of further damage and increasing costs.