## Modeling the Evolution of Construction Solutions in Residential Buildings' Thermal Comfort
### Evolution of Constructive Solutions and Thermal Comfort  
For many years, construction was dependent on the existing natural resources in the different regions and in the prevailing climatic conditions [20; 21]. In the last century, the use of regional natural materials was reduced, being massively replaced by brick and cement [21]. In addition to the materials, techniques have also evolved. For instance, the changes in the construction of external walls are extreme, leading to a considerable decrease in buildings' thermal inertia and a consequent worsening of thermal comfort conditions (Figure 3). The high-thickness cloths of stone masonry were replaced over the years by lighter and cheaper materials, such as brick [22]. In the 1980s, thermal insulation materials started to be introduced and, since then, different outside and inside thermal insulation systems have been developed to cope with increasing thermal performance requirements [23]. Roofing [24; 25], flooring [26] and glazing spans [27; 28] solutions have also evolved, and it is currently common the usage of insulating materials to increase the thermal resistance of these constructive elements. Figure 2: Evolution of the _U-values_ of the main constructive elements in Portugal (Retrieved from: [[http://www.entranze.eneralata.eu/#/u-values.html](http://www.entranze.eneralata.eu/#/u-values.html)]([http://www.entranze.eneralata.eu/#/u-values.html](http://www.entranze.eneralata.eu/#/u-values.html)) (accessed on 24 September 2020)). More recently, lightweight steel-framed (LSF) systems have been attracting interest as these prefabricated modular steel structures are assembled on site, reducing significantly both construction time and costs [29; 30]. However, the low thermal mass is one of the most relevant drawbacks of these constructions, giving rise to noteworthy daily temperature oscillations (particularly felt in Mediterranean climates) which, in turn, cause high thermal discomfort [31]. Several strategies can be used to improve the thermal resistance of LSF elements, being the use of phase-change materials (PCMs) one of them. In refurbishment processes, PCM boards can be added to walls, without changing considerably the existing design, while in new constructions several options are available, namely by encapsulating these materials in the building elements [30; 32]. PCMs have unique properties that allow them to increase the thermal inertia of buildings without increasing the weight of the structures [32; 33]. A building's thermal comfort influences the welfare, health and productivity of its occupants and, therefore, it has been a topic widely addressed both from the literature and legislation standpoints [34]. Constructive solutions play a key role in occupants' thermal comfort as they must allow adequate indoor-outdoor heat transfer [35], ensuring that heat losses through the envelope in winter are minimized, whereas solar gains through glazing spans and internal loads are enhanced [35]. Conversely, in the summer, solar gains entering buildings by both opaque and glazed elements must be minimized, and internal loads should be removed [36]. However, the evolution of constructive solutions has been accompanied by a loss of thermal mass, yielding a negative influence on the buildings' thermal performance [37], thereby opposing the increase in thermal comfort requirements. Thus, the evaluation of buildings thermal characteristics gains special relevance as constructive elements can be responsible for minimizing heat gains and losses, and for creating thermal inertia, contributing to enhance thermal comfort. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), thermal comfort can be defined as \"_that condition of mind which expresses satisfaction with the thermal environment_\" [38]. According to this description, comfort conditions are thus variable from person to person and influenced by physical and physiological processes, in addition to cultural, environmental and personal factors [5].