Abstract
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.
Highlights
Global society is increasingly aware of the need for a systematic change in all sectors of the economy to reduce the environmental impacts created by human activity and the building sector must take an active part in the change
The European Directive on the Energy Performance of Buildings (Directive 2010/31/EU) required that all new public buildings should be nearly zero-energy by 2018 and likewise all buildings by the end of 2020 [2]. nZEB refers to buildings which generate the same amount of energy as they consume over a specific period [3]
A condensation analysis has been carried out to see in which cases it is necessary for the airtight sheet to have vapour barrier characteristics
Summary
Global society is increasingly aware of the need for a systematic change in all sectors of the economy to reduce the environmental impacts created by human activity and the building sector must take an active part in the change. In Europe, it is responsible for approximately 36% of all CO2 emissions, and almost 50% of final energy consumption is used in heating and cooling, of which 80% is consumed in buildings [1]. Reducing energy demand firstly requires the implementation of design strategies and control of passive building measures. These include the correct orientation of the building, increasing thermal insulation, reduction of uncontrolled air infiltration, natural ventilation and use of the thermal inertia of the building envelope [9]
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