Purcell is happy to share the news that the Great South Window in Canterbury Cathedral has won the RICS South East region Building Conservation award.

The restoration of the mediaeval stained glass south transept window required extensive work over seven years. The conservation of Canterbury Cathedral, a grade I listed world heritage site and scheduled ancient monument, is overseen by Surveyor to the Fabric and Purcell Partner Jo Deeming.

The Great South Window in Canterbury Cathedral © Canterbury Cathedral

Standing 55ft high and 24ft 9inches wide, the 1420’s Great South Window holds precious mediaeval glass, including the 12th century ‘Ancestors of Christ’.

Four years of research and development revealed issues with failing mediaeval drains, unstable groundwater levels, corroding ironwork and the impact of previous campaigns of building work. Understanding these characteristics was essential to developing the conservation strategy.

With support scaffold restricting access, the cleaning, setting out, measuring, protection, dismantling, repairs and reinstallation all had to be undertaken by the Cathedral’s masons and glaziers by hand. Many of the stones weighed more than 250kg, some were half a tonne.

All historic deformities had to be reconstructed exactly, to allow the historic glass to be re-fitted unaltered. Bespoke tools for setting out were developed and manufactured, the success of which is evidenced by not a single glass panel needing to be adjusted upon reinstallation.

Canterbury Cathedral © Richard Chivers

Sustainability is at the heart of Canterbury’s conservation ethos of ‘as much as necessary but as little as possible’. During construction, the entire support scaffold was enclosed to facilitate all-year working and regular worship continued within the Church throughout the project.

The Caen limestone used for repairs was tested to match the characteristics of surviving mediaeval fabric. Sawn on site and banked and carved by hand, stone chippings and dust were re-used by the mason’s shop in the formation of traditional lime mortars.

Continuing a centuries old tradition, all conservation works were undertaken on site by the Cathedral’s in-house crafts men and women. The project sustained six stone masonry apprentices, honing their conservation and carving skills and now qualified as stonemasons.

By Jess McCulloch