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It is often assumed that reduced heat flux to a ventilated attic reduces the temperatureand thereby increases the relative humidity. Consequently, the importance of having atight air and vapour barrier in the ceiling becomes more important with increased insu-lation. Therefore, in Denmark, the recommendation is to have a tight vapour barrierwhen re-insulating ceilings against cold ventilated attics to a total of 150-mm insulationmaterial. The recommendation is independent of the insulation material’s hygroscopicproperties or the indoor moisture level. The aim of this project was to test the rele-vance of the recommendation through testing in a full-scale test building (7322 m) witha series of six different ceilings with or without a vapour barrier and variation in theinsulation material comprising insulation thickness and its hygroscopic properties. Theexamination was performed with a controlled indoor climate after an European humid-ity classes 1–3 and a natural outdoor climate. The study showed very little differencesin temperature and relative humidity in the cold ventilated attics, while the humidityclass of the indoor climate significantly affects the absolute moisture content in the attic.However, the climate in the attic did not cause mould growth in the test sections, evenfor humidity class 3. Consequently, in the test building the thickness or hygroscopic1Danish Building Research Institute, Aalborg University Copenhagen, Copenhagen, Denmark2Department of Mathematical Sciences, Aalborg University, Aalborg, DenmarkCorresponding author:Thor Hansen, Danish Building Research Institute, Aalborg University Copenhagen, A.C. Meyers Vænge 15,2450 Copenhagen, Denmark.Email: thh@sbi.aau.dkproperties of the insulation material did not have a significant effect on the moisturelevel in attics and did not determine whether a vapour barrier should be installed. In thisstudy with the given climate, a vapour barrier is unnecessary in well-ventilated attics ifthe ceiling is airtight. It is often assumed that reduced heat flux to a ventilated attic reduces the temperatureand thereby increases the relative humidity. Consequently, the importance of having atight air and vapour barrier in the ceiling becomes more important with increased insu-lation. Therefore, in Denmark, the recommendation is to have a tight vapour barrierwhen re-insulating ceilings against cold ventilated attics to a total of 150-mm insulationmaterial. The recommendation is independent of the insulation material’s hygroscopicproperties or the indoor moisture level. The aim of this project was to test the rele-vance of the recommendation through testing in a full-scale test building (7322 m) witha series of six different ceilings with or without a vapour barrier and variation in theinsulation material comprising insulation thickness and its hygroscopic properties. Theexamination was performed with a controlled indoor climate after an European humid-ity classes 1–3 and a natural outdoor climate. The study showed very little differencesin temperature and relative humidity in the cold ventilated attics, while the humidityclass of the indoor climate significantly affects the absolute moisture content in the attic.However, the climate in the attic did not cause mould growth in the test sections, evenfor humidity class 3. Consequently, in the test building the thickness or hygroscopic1Danish Building Research Institute, Aalborg University Copenhagen, Copenhagen, Denmark2Department of Mathematical Sciences, Aalborg University, Aalborg, DenmarkCorresponding author:Thor Hansen, Danish Building Research Institute, Aalborg University Copenhagen, A.C. Meyers Vænge 15,2450 Copenhagen, Denmark.Email: thh@sbi.aau.dkproperties of the insulation material did not have a significant effect on the moisturelevel in attics and did not determine whether a vapour barrier should be installed. In thisstudy with the given climate, a vapour barrier is unnecessary in well-ventilated attics ifthe ceiling is airtight.

The transfer of particulate and gaseous pollution from hidden fungi growing on non-visible surfaces within the building envelope to occupied rooms is limited by the separating structure. Yet, growth, even in sealed construction cavities, is known to cause annoying smells and other more adverse health symptoms among the building occupants. This study analyses limitations of air change rate measurements in inaccessible construction cavities as well as analyses of the air exchange between living areas and accessible cavities such as crawl spaces and attics. It was necessary to invent a field study technique to use the tracer gas decay method in small and inaccessible cavities. This technique allowed further investigation on the exposure risk from hidden fungal growth. Assessment of the air transfer between crawl spaces and living areas indicate that the tightness of separating structure has an influence on the exposure risk.