Climate change is having a significant and growing impact on environments and communities worldwide. As well as documenting and analyzing the causes of these changes, the IPCC [1] has published numerous scenarios of the upheavals we need to prepare for, but it is only fairly recently that it has examined the consequences of climate change on heritage. Similarly, based on the work of ad hoc Icomos and Unesco groups, COP 26 and COP 27 have come to focus on heritage in 2021 and 2022 respectively. For built heritage - as for tangible and intangible heritage - the main challenge is to evolve to adapt to climate change and to participate positively in it, while maintaining their value. What can be done? The building sector is the biggest consumer of energy and the biggest emitter of greenhouse gases. Even before the onset of the global energy crisis in 2022, France had adopted a draft national low-carbon strategy and environmental regulations applicable to new buildings. This regulation RE2020 [2] encompasses the entire life cycle of a building, including the measurement of greenhouse gas emissions from the extraction and transportation of materials, logistics, construction and operation ("operational" carbon emissions calculated over 50 years), end-of-life and recycling. In this respect, most of our built heritage is quite virtuous, since the emissions associated with its construction are part of the past. In some cases, we can even speak of a carbon payback, as the building shell has already been amortized by past centuries. Thus, energy consumption is mainly due to the use of the premises. Old buildings, sometimes referred to as "heatwasters", raise questions and controversy. We need to explain and demonstrate the urgency of adapting an appropriate diagnosis to old buildings, taking into account the diversity of materials used and architectural techniques. The aim is to keep at least 80% of the old buildings intact [3], particularly the structures and facades, and to target and minimize interventions - starting from the premise that conservation is in itself a "green" act.
