The timber roof structure of Chapel XVI at Sacro Monte of Orta: an example of conservative strengthening work

The principles of conservation of existing structures (like evidence of regional construction techniques) pose a significant challenge in the general field of structural safety, increasingly claimed by the new technical codes. The restoration building site of Chapel XVI at Sacro Monte of Orta San Giulio (Italy) testifies to a respectful design approach to enhance the timber elements still recoverable without distorting the original static scheme. The preliminary knowledge phase allowed for correctly interpreting the historical construction phases (including analysis of archival documents and diagnostic investigations), the vulnerabilities of the roof structure, and the peculiarity of the stone roof covering as a construction technique to be preserved and improved. The recovery project has exploited the potential of the laser scanner and micro-invasive diagnostic techniques to move towards limited replacement choices of wood elements that could no longer be recovered. The recovery of the roof of the XVI Chapel, as a pilot building site of an international research project on the maintenance of historical sites (INTERREG ITA-CH “Main10ance”), is evidence of a fruitful multidisciplinary discussion aimed at improving the methodological approach to the strengthening work of historical structures.