Canterbury Cathedral Archive holds the Cathedral’s archives dating back to the 8th century. It also holds the historic records of Canterbury City Council, the Diocese of Canterbury and the East Kent parishes. Our role in the project related to the installation of a new Westmoreland slate roof to replace the existing leaking copper roof. The new slate roof was considerably heavier than the copper with the existing steel truss also supporting a large vaulted plaster ceiling, thus it was necessary to model the structure to take account of the increased loading. To limit the deflection of the plaster ceiling, our analysis showed strengthening of the steel truss would be required. The steel strengthening works were carried out and the project completed in February 2013.