Air change rate in ventilated attics – reality and input for simulations

Eva B. Møller*, Martin Morelli, Thor Hansen

*Corresponding author for this work

Research output: Contribution to book/anthology/report/conference proceedingArticle in proceedingResearchpeer-review

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To remove moisture by ventilating constructions is a well-known strategy, used successfully in numerous facades and roofs. However, simulating ventilation is often difficult as convection in this case is in another dimension than what is usually in focus in 1D hygrothermal simulations. There are strategies for simulating ventilation in 1D programs assuming a fixed air change rate (ACH). Unfortunately, ACH in roofs highly depend on wind direction and speed, hence a constant rate is a gross simplification. The article describes a comparative study between simulations with a 1D hygrothermal simulation program (WUFI) and simulations with BSim, a program in which the indoor climate can be simulated in different zones, in this case the ventilated attic. Focus is the effect of ACH in the attic on temperature and relative humidity. Finally, measurements of ACH in attics of ten single-family houses are presented. These measurements show that average ACH measured over more than two weeks differ very much from house to house although the ventilation openings in all houses seemed to be in accordance with current guidelines. Even measurements of the same attic differ considerably from time to time. The paper discusses what implications this should have on simulations.
Original languageEnglish
Title of host publication MATEC Web of Conferences : 4th Central European Symposium on Building Physics (CESBP 2019)
EditorsR. Černý, J. Kočí, V. Kočí
Number of pages6
Place of PublicationPrague, Czech Republic
PublisherEDP Sciences
Publication dateSep 2019
Article number02073
Publication statusPublished - Sep 2019
EventCentral European Symposium on Building Physics 2019 - Faculty of Civil Engineering, CTU in Prague Thákurova 7 166 29 Prague, Czech Republic, Prague, Czech Republic
Duration: 2 Sep 20195 Sep 2019
Conference number: 4


ConferenceCentral European Symposium on Building Physics 2019
Location Faculty of Civil Engineering, CTU in Prague Thákurova 7 166 29 Prague, Czech Republic
Country/TerritoryCzech Republic
Internet address
SeriesMATEC Web of Conferences


  • ventilation
  • attic
  • insulation


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