Hygrothermal conditions in ventilated attics with different air change rates and ceiling constructions

Martin Morelli*, Eva Møller, Thor Hansen

*Corresponding author for this work

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    Abstract

    A recently Danish study reported that no vapour barrier is needed in ceilings, if the attic is well ventilated and the ceiling towards the dwelling is airtight. Based on that study, new investigations were initiated with focus on the hygrothermal behaviour in ventilated attics with different air change rates. A test house with three sets of four different ceiling constructions - all airtight - was used in this study. The ventilation rate was reduced in two of the sets with approx. 35 % and 50 %, respectively. Air change rates were measured with tracer gas. Furthermore, temperature and relative humidity was measured every hour. Measurements in similar ceilings with mineral wool or cellulose-based insulation material show that hygroscopic properties of the insulation have very limited effect on relative humidity. Furthermore, only at low ventilation rate the effect of a vapour barrier could be measured with minor impact. Based on the short-measured period the calculations of the risk of mould growth showed no risk. The results indicate that even when the ventilation is reduced by 50 %, the ventilated attic still performs well if the ceiling is highly airtight. However, the importance of vapour barriers becomes more important at lower air change rates.
    Original languageEnglish
    Article number07008
    JournalE3S Web of Conferences
    Volume172
    Number of pages7
    ISSN2267-1242
    DOIs
    Publication statusPublished - 2020
    Event 12th Nordic Building Physics Conference - Tallin University of Technology, Tallin, Estonia
    Duration: 7 Sept 20209 Sept 2020
    Conference number: 12

    Conference

    Conference 12th Nordic Building Physics Conference
    Number12
    LocationTallin University of Technology
    Country/TerritoryEstonia
    CityTallin
    Period07/09/202009/09/2020

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