Hygrothermal performance of cold ventilated attics above different horizontal ceiling constructions: Full-scale test building

Thor Hansen*, Eva B. Møller, Torben Tvedebrink

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

3 Citations (Scopus)

Abstract

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.dk
properties 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.
Original languageEnglish
JournalJournal of Building Physics
Volume44
Issue number1
Pages (from-to)67-91
Number of pages25
ISSN1744-2591
DOIs
Publication statusPublished - Jul 2020

Keywords

  • Cold ventilated attics
  • insulation material
  • moisture
  • mould growth
  • vapour barrier

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