Climate-resilient restoration strategies
When it comes to restoring historic buildings, the current guiding principle is to preserve as much of the original structure as possible. To achieve this, the ETH Zurich researchers are studying how exactly the sandstone becomes damaged. Water plays a key role in all degradation mechanisms, and much of this comes through rain. While vertical rain can be managed by architectural interventions, wind-driven rain cannot. Exposure to such rain, but in particular extreme events of fast and extreme wetting, followed by rapid drying appears to be a key factor in degradation and is very location-specific.
During such events, moisture penetrates the clay-bearing sandstone used to build the cathedral and causes damage through processes such as swelling, salt crystallisation and freezing. To study how damage occurs and examine the influence of air pollution, the ETH Zurich researchers have been measuring wind-driven rain and the local microclimate, as well as moisture profiles within the stones over a number of years using a network of sensors around the cathedral.
Alongside this, ETH Zurich researchers are also developing a model to correlate local exposure, in particular wind-driven rain, to the observed forms and extents of damage. Experts could use this as a tool to predict how damage may change in the future, not just as a result of the course of time, but in relation to climate changes, in particular the nature, intensity and frequency of extreme events around the cathedral. They could then use this information as a basis to develop tailored restoration strategies and improve the durability of restoration measures, anticipating the consequences of climate change, which represents a real challenge for practitioners.
Applicable to other buildings
The use of digital tools such as 3D models or Heritage Building Information Modelling is nothing new in built heritage. However, the “Heritage++” project takes this one step further by integrating information from various disciplines, with a focus on conservation, allowing it to be used interactively and also making it possible to include conservators’ practical knowledge and expertise. In the future, the digital co-pilot, as applied in Lausanne Cathedral, could also be used for other sandstone monuments, such as bridges, castles or monasteries, and, in the medium term, for buildings made from other construction materials.
Christophe Amsler, the architect responsible for Lausanne Cathedral, believes that digital technologies will become an integral part of conservation work: “Preserving historic monuments requires constant care and attention. Advances in technology can help us to repair and keep these buildings living, but at the same time, we need to remain faithful to the original spirit and heritage of the monument.”