###### Abstract
Apart from in situ measurements, they performed a numerical analysis with WUFI PRO and also evaluated, after a retrofitting, the increase in the mean wall temperature due to the insulating effect of the aerogel-based rendering, and after it dried out, the lowering moisture content as a result of the unhindered permeation of moisture through the vapor permeable aerogel rendering. In the paper, the authors declared that better interior comfort was reached as a result of the positive impact of aerogel rendering on the air temperature in a room and the temperature on the inner surface of the coldest wall. [PERSON] et al. [18] studied several base formulas to identify the ideal aerogel insulating plaster/render mix; they also analyzed the thermal behavior of typical wall assemblies that had been retrofitted using a novel aerogel-based plaster through numerical simulations. The aim was to investigate the thermal performance of a conventional solid wall retrofitted with the aerogel plaster, considering dynamic hygothermal conditions. [PERSON] et al. [19] analyzed the effects of the application of insulating materials on the energy refurbishment of buildings aimed at improving the thermal transmittance of the envelope. The study highlighted that if these actions are not planned and executed accurately, the drying potential of a wall is reduced, and thus, its original features are modified, and it is generally left in a humid state. Moreover, the authors affirm that it has become essential to perform hygothermal assessments. [PERSON] et al. [20] analyzed two different plasters in order to consider the potential of earnthen materials to improve indoor comfort and to reduce energy consumption for climatization; the thermal performance and water vapor permeability were taken into account in order to analyze the comfort conditions during summer periods, without the installation of any HVAC system. [PERSON] et al. [21] developed and applied a bio-based insulation material to minimize the environmental impacts of existing buildings through a reduction of the embodied and in-use energy demand. The study showed that the hygothermal performance of natural building material has direct and indirect impacts on moderating the indoor environmental conditions and can contribute to energy saving. [PERSON] et al. [22] studied the application of active/hydrophilic capillary insulation to solve the moisture problems that usually arise in the internal insulation of an external wall. This insulation is able to transport liquid moisture to the inner surface and enable the wall to dry. [PERSON] [23] investigated dampness problems, which are known to be the main cause of masonry deterioration in historical buildings. They investigated the moisture transfer dynamics to and from the walls and columns constituting the masonry of Crypt of the Cathedral of Lecce. Despite the amount of research focused on the hygothermal behavior of historic building envelopes, the scientific literature still lacks comprehensive studies which combine the analysis of hygothermal behavior, energy efficiency and indoor thermal comfort to support the design of the retrofit actions. For these reasons, the aim of this research has been to provide a methodological approach that could be applied during retrofitting projects. The study also assesses the impact of different retrofitting solutions on thermal comfort, energy performance and hygothermal compatibility. In addition, this work provides useful guidelines for defining indoor insulation retrofitting actions on historic buildings through a multi-level approach involving heat and moisture studies and dynamic BES (building energy simulation) analyses. The opportunity of such a case study arose from the rehabilitation competition of the Monastero de Santa Maria de Monfero in Galicia, Spain, the winning project of which was studied by the Authors as part of an MSc thesis [24] (Figure 1). The competition for the renovation and transformation of the monastery into a spa hotel started in 2004.