The intervention on historic buildings through building energy retrofitting has become one of the current challenges of improving energy efficiency. Nonetheless, this building typology presents certain complexities. Among them, one of the most relevant is the protection on their façades due to the historical and/or artistic values of a given façade and, therefore, the addition of external thermal insulation is restricted. However, at the same time, in several of those buildings indoor surfaces do not present that architectural value, and then internal thermal insulation becomes a promising strategy for improving their thermal performance. Nevertheless, its application must be carefully evaluated to avoid possible pathologies caused by moisture problems. This paper aims to identify constructive solutions for interior insulation of walls free from moisture problems. For this purpose, a comprehensive analysis of a series of constructive solutions based on internal insulation has been carried out through hygrothermal simulations. The results show how the application of water-repellent impregnation becomes essential to guaranteeing the integrity of the envelope. In addition, the combination of insulations with or without inner membranes, such as smart vapor retarders or vapor diffusion barriers, has been evaluated detecting the solutions that best fit the objective. Finally, taking advantage of the great potential of 2D simulation tools, the post-processing of the data has been performed to apply the wood decay model, and thus assess the behavior of a very conflictive point in this type of intervention, i.e., the wooden beam-ends. The results in this critical point have shown how the application of the proposed constructive solutions becomes essential to guarantee the integrity of the element and how the application of traditional solutions could lead to a hazard that must be avoided.

European Building Codes have transitioned towards Net Zero Energy Building (NZEB) requirements in new constructions, demanding high levels of insulation and airtightness derived from research and standards developed in Northern and Central Europe. The use of these principles in Southern Europe, where solar radiation is greater and building typologies and user behaviour are different, may have had a negative impact in Thermal Comfort and Energy Demand and Consumption. In this study, six dwellings located in a 2018 27-storey Passivhaus-certified building were monitored for a period of 9–18 months in 2019 and 2020. In the spirit of a complete Post-Occupancy Evaluation, a User Comfort Survey was carried out. The obtained data were analysed and fixed-limit and adaptative comfort models were used to assess the compliance of several European Comfort Standards, namely, EN ISO 7730, EN 15251, CIBSE TM:52, CIBSE TM:59 and CIBSE Guide A. Experimental results confirmed the issues reported by occupants in the Comfort Survey, making evident a severe overheating problem which we were able to quantify. In addition to presenting the obtained data and its analysis, this paper discusses the plausible causes and health-related implications of excess heat in NZEB Housing in the Northern Spanish climate.

In the last decade, several European directives have been established to contribute to the 2020, 2030 and 2050 energy saving targets and impose energy efficiency requirements for new construction, existing buildings and building renovation operations. One of the ways to achieve said objectives is to rely on the most demanding energy efficiency labels existing in Europe, such as Passivhaus, and to implement similar concepts into the national energy regulations of European countries based on a high-performance thermal envelope (high insulation and high-performance windows), high airtightness and high-performance heat-recovery ventilation systems, and solar heat harvesting. This energy conservation concept has shown to be effective for houses with low-density occupation in cold climates, but may cause severe overheating problems in denser collective housing in temperate and hot climates with higher solar radiation. To assess this impact, five flats in three developments from different periods that range from no insulation at all to a nZEB, Passivhaus-certified high-rise are compared in this paper, using data from a monitoring campaign during the summer of 2020. The results show and quantify the strong impact the evolution of the energy saving regulatory trend has had on summer indoor comfort, which may in some cases lead to previously unnecessary air conditioning for cooling and, ultimately, be counterproductive towards the end goals of reducing energy consumption and greenhouse-effect gas emissions and mitigating climate change.

The COVID-19 pandemic has generated a renewed interest in indoor air quality to limit viral spread. In the case of educational spaces, due to the high concentration of people and the fact that most of the existing buildings do not have any mechanical ventilation system, the different administrations have established natural ventilation protocols to guarantee an air quality that reduces risk of contagion by the SARS-CoV-2 virus after the return to the classrooms. Many of the initial protocols established a ventilation pattern that opted for continuous or intermittent ventilation to varying degrees of intensity. This study, carried out on a university campus in Spain, analyses the performance of natural ventilation activated through the information provided by monitoring and visualisation of real-time data. In order to carry out this analysis, a experiment was set up where a preliminary study of ventilation without providing information to the users was carried out, which was then compared with the result of providing live feedback to the occupants of two classrooms and an administration office in different periods of 2020, 2021 and 2022. In the administration office, a CO₂-concentration-based method was applied retrospectively to assess the risk of airborne infection. This experience has served as a basis to establish a route for user-informed improvement of air quality in educational spaces in general through low-cost systems that allow a rational use of natural ventilation while helping maintain an adequate compromise between IAQ, comfort and energy consumption, without having to resort to mechanical ventilation systems.

Overheating in buildings is a growing challenge in temperate climates, even in those where the traditional design focus was on protecting from cold and winter energy savings. This paper addresses a collateral problem that arose during the study of overheating in a residential Passivhaus building in Bilbao, northern Spain. Specifically, the local climate of three laundry spaces was investigated, where high daytime and nighttime temperatures were recorded. An extensive monitoring campaign was carried out with different durations up to more than 21,000 h over four years, and the collected data were compared with outdoor climatic conditions. The results allowed for characterizing the thermal behavior of these semi-outdoor spaces and show the magnitude of the problem, quantifying it. Laundry spaces were confirmed to be hotter and dryer than the outdoor climate almost always. The mean average difference between the monitored rooms and the exterior was quantified to be around positive 5 °C during both daytime and nighttime. Extreme heat events were documented, with maximum temperatures above 50 °C and temperature differentials of up to 15.85 °C. In addition, this article comments on the impact of overheating these laundry spaces on the interior of the dwellings, pointing out the differences between the assumptions made during the design phase of the project and the observed or measured reality. Questions were raised about the possible implications of the peculiar performance of these semi-outdoor spaces on the mechanical heat recovery ventilation system (MHRV). The data presented in this article revealed and quantified a design flaw that went unnoticed by all agents involved in the planning, design, and construction of the 361-apartment project. The inability to predict the behavior of the studied spaces has had a negative impact on building performance during the summer months and has prevented the implementation of strategies that could have been beneficial in other periods. A thorough analysis of the thermal behavior of similar spaces becomes essential to prevent performance gaps in future projects and to inform adequate building modeling in the design stages.

The Administration of the Basque Country has been responsible for public housing since 1981. Since then, more than 104,000 protected housing units have been built for 2,200,000 inhabitants, 34,000 of which have been directly promoted by the Basque Government. To better adapt its policies to the requirements of a new contemporary society, the Housing Department of the Basque Government has developed a new Habitability Decree in 2022. This Decree aims to update housing to the new ways of living in Basque society and to incorporate new social requirements regarding housing, such as universal accessibility, gender perspective, productive housing, and remote work, while trying to open new ways to improve flexibility of the housing stock. This article analyses some of the key aspects of the new Decree and one of the newly regulated typologies for temporary housing aimed at young and older populations. In addition to the critical selection of the most relevant aspects of the Decree, this article aims at contextualising its requirements in the European context and the broader reference framework of the housing crisis in the Basque Country. To that end, the most notable novelties of the Decree are presented alongside the analysis of 13 temporary housing projects developed by the Housing Department before the approval of the Decree, placing special emphasis on the issue of over-occupation. The analysis makes it possible to typologically characterise the temporary accommodation built to date and to compare the new minimum living space requirements per person with other international regulations. As a conclusion, a discussion is offered about the usefulness of the Decree for adapting new housing in the Basque country to the 21st century, and for preventing the issue of overcrowding.