Guidelines for selecting roofing slate for the restoration of historical buildings and monuments: Two case studies

Slate has been used for centuries as a building material, and many historical buildings and monuments use slate in roofs and structures. When slate roofs must be totally or partially replaced, the structural and aesthetic integrity of the building as a whole must be guaranteed, based on both international criteria for restoration, and on current local legislation regarding historical buildings. For selection of the most appropriate type of slate to use in the restoration of historical slate roofing, we propose the following steps: a) study of the roof's state, b) spectrophotometric determination of the texture and colour of the original slate, c) petrographic study and determination of the weatherability of the replacement slate, and d) location of the original slate quarry area. With all these data it is possible to choose the most suitable type of commercial slate for replacing the original slate. Thus, even in the absence of historical information, with this four-stage process a replacement slate for building restoration can still be selected on clear and justifiable grounds. The present article uses this methodology to examine two case studies of roofing slate restoration.