The air-tightness of the thermal envelope of buildings is one of the measures to reduce their energy demands in order to achieve global warming reduction targets. To this end, airtight sheets with different water vapour permeability characteristics are used. The different products studied are highly dispersed in terms of equivalent air thickness values, leading to confusion. After the analysis carried out, it is concluded that all airtight sheets are vapour barriers. To clarify whether or not these sheets are necessary as vapour barriers, a condensation analysis was carried out on 13 different facades for 3 climate zones with severe winters as defined in Spanish regulations. The results reveal that interstitial condensation occurs in only 7 of the 39 case studies, with the traditional facades of brickwork with render causing the greatest problems if the appropriate products are not used. In these cases, airtight sheets with water vapour barrier characteristics must be applied on the interior face of the insulating material. In all other cases (32), the airtight sheets must be permeable to water vapour if it is looked for a more breathable wall to water vapour and a better control of the interior humidity conditions.

This research evaluates the improvement in thermal comfort in a home located in a cold region through the implementation of a thermal envelope with insulation, considering its economic viability and its impact throughout the building's useful life. An exploratory quantitative methodology is adopted, using the case study technique. A convenience non-probability sampling was used. The study was conducted over four months during the summer season and consists of four phases: regulatory analysis, assessment of the current state, implementation of a prototype envelope with thermal insulation, and analysis through monitoring. To this end, data loggers were used to measure temperature and relative humidity fluctuations in two comparable rooms: one intervening and one control. The results showed an average increase of 2°C in the interior temperature and a 10% reduction in relative humidity in the intervened room, allowing compliance with the EM110 standard, whose current minimum conditions do not guarantee interior thermal comfort. This evidence suggests the need to readjust the thermal envelope criteria in said regulation. Overall, the experience demonstrates the positive impact of passive strategies for improving thermal comfort in existing homes, proposing a replicable and low-cost approach that can be considered in future regulatory updates in the country.

The energy rehabilitation of listed buildings guaranteeing heritage values but allowing a use that contributes to their conservation, supposes a challenge with the need of a holistic approach. Buildings of the Modern Movement, many of which are registered as DOCOMOMO (DOcumentation and COnservation of buildings, sites and neighbourhoods of the MOdern Movement), are a particular case since many of them are not yet listed or are under unclear requirements. This paper explores the inclusion of a cost-effective methodology as part of the decision-making in the energy rehabilitation of these DOCOMOMO buildings, applying it to the case study of an office building located in the north of Spain. Different scenarios were studied balancing cost-effectiveness, energy efficiency and rehabilitation requirements. In this case study, the analysis may allow policymakers to have supportive arguments to subsidize certain elements (as e.g., steel frames), or allow the use of alternative options with similar aesthetic characteristics, but at a much lower cost. This second option will constitute the unique cost-effective scenario, with energy savings of between 25.36 % and 38.8 %. The inclusion of a cost-effective methodology as part of the mechanics for decision-making in the energy refurbishment of DOCOMOMO buildings permits the optimisation of the intervention guaranteeing their use and the conservation of heritage values.