###### Abstract  
The energy refurbishment of historic buildings is a complex task for building envelope designers who need to carefully consider building conservation guidelines and principles. In most cases, external wall insulation techniques can determine an unacceptable alteration of the historical value of a building. For this reason, internal wall insulation techniques have been used widely in the last few decades. Nevertheless, dealing with internal wall insulation requires a complex design to avoid the risk of condensation and moisture-related pathologies. Moreover, an internal wall insulation may have a relevant impact on indoor comfort conditions. In this paper, the Monastery of Santa Maria de Montero in Galicia (Spain) has been adopted as a building case study to compare different technological solutions based on: (i) an insulating plaster layer, (ii) dry counter wall systems. In the first step, heat and moisture transfer simulations of the wall components were performed to analyze the hydrothermal behavior of the different alternatives considering two different climate conditions. In a second step, a simulation of the whole building was performed to analyze the impact of the retrofitting strategies on the indoor climate and on the building heating and cooling demand. The obtained results show that the counter wall solution leads to higher energy savings during the heating season in the colder winter climate. However, the use of insulating thermal plaster could also be a viable solution since they lead to several advantages in summer because of their higher thermal inertia. Therefore, the selection of the most appropriate insulation technique has to be evaluated carefully considering the outdoor/indoor climate and using a case-by-case approach. cultural heritage; hygrothermal performance; thermal plaster; interior insulation; stone construction; energy saving; thermal comfort; thermal transmittance +
Footnote †: journal: Applied Sciences  
_Applied_  
_Accepted: 11 August 2021_  
the historical value. Moreover, each technological intervention should not only be cost-effective, but also be acceptable to the final user, in terms of the level of provided thermal comfort [7]. One of the main constraints to the design phase of retrofitting interventions on historic buildings is the actual feasibility of such interventions. In most cases, the external envelope cannot be modified, due to the architectural value of the building; thus, the use of external insulation systems is precluded. On the other hand, internal insulation strategies are considered a more viable alternative, although they can still be quite invasive when new materials are introduced or historic linings are replaced. A further concern about internal insulation is its physical compatibility with traditional constructions, since changing the balance between heat, air and moisture can affect a building's integrity ([PERSON] and [PERSON], 2013) [8]. Traditional buildings are formally defined, in UK regulations, as \"buildings of traditional construction with permeable fabric that both absorbs and readily allows the evaporation of moisture\" [9]. Historic buildings have different bioclimatic and vernacular characteristics. These buildings may have complex and irregular geometries, they may have been built with non-standardized materials and may be heterogeneous in their composition. Given these differences, the solutions adopted for energy retrofitting in contemporary buildings may not be appropriate for historic buildings and may even damage them, thereby resulting in the loss of our collective cultural heritage [9]. Since dampness is the main cause of masonry deterioration in many historic buildings, controlling the moisture behavior of building enclosures has been a topic of growing interest, especially over the last 15 years [10]. However, the behavior of moisture is often difficult to predict, partly due to the complexity of moisture models, which are rarely introduced into monitoring plans.