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 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.

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.

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This paper delves into the examination of indoor comfort in classroom environments and its interplay with ventilation on human wellbeing in scenarios of varying indoor carbon dioxide concentrations. The assessment of these parameters was done according to the provisions outlined in the Spanish national Regulation of Thermal Installations in Buildings (RITE). This study also compares various ventilation strategies, namely natural, mechanical and hybrid ventilation, commenting the pros and cons of each method in the climate of the Basque Country, Spain. To do so, a classroom in the School of Architecture of San Sebastián was modelled in thermal simulation software. Simulations were carried out for full days in 5-minute intervals using Design Builder, and considered three different exterior scenarios (a cold day, temperate day, and a warm one) and three different ventilation systems (natural, mechanical with heat recovery, and hybrid). Two additional scenarios where added for control, one with no ventilation at all and another with a partial, constant, natural ventilation, like was done during the COVID-19 pandemic. Thus, the natural ventilation option was evaluated under three conditions (windows always closed, windows open 15%, and windows operated by thermal sensation of the user). The mechanical system evaluated consisted of a constant flow ventilation for IDA 2 IAQ with an airflow of 12.5 l/s·person. The modelled hybrid system consisted in a combination of simple flux mechanical ventilation and open windows and doors under some particular conditions. An occupancy rate of 50% of the theoretical maximum occupancy of the classroom and a heating setpoint of 15ºC were considered. This article presents the CO2 concentration, final energy consumption and thermal comfort results obtained in the simulation and compares between the different scenarios. The results showed that the hybrid ventilation system was able to effectively control indoor air quality, providing a healthy and comfortable environment for occupants. The hybrid system demonstrated improved energy efficiency compared to the natural ventilation system, while maintaining a high level of indoor air quality. Overall, the results of this study highlight the importance of considering hybrid ventilation in educational spaces in the northern Basque Country climate. The study provides valuable insights for building design and operation, especially for renovation of existing schools and educational facilities that lack any means of mechanical ventilation, showing some of the potential for hybrid ventilation to improve indoor air quality and energy efficiency.