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

Martin Morelli, Eva B. Møller, Thor Hansen

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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
Title of host publication12th Nordic Symposium on Building Physics (NSB 2020)
EditorsJ. Kurnitski , T. Kalamees
Number of pages7
PublisherEDP Sciences
Publication date30 Jun 2020
Pages1-7
Article number07008
DOIs
Publication statusPublished - 30 Jun 2020
Event12th Nordic Symposium on Building Physics, NSB 2020 - Tallinn, Estonia
Duration: 6 Sep 20209 Sep 2020

Conference

Conference12th Nordic Symposium on Building Physics, NSB 2020
Country/TerritoryEstonia
CityTallinn
Period06/09/202009/09/2020
SeriesE3S Web of Conferences
Volume172
ISSN2267-1242

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

    Møller, E. B., Morelli, M. & Hansen, T., Sep 2019, MATEC Web of Conferences: 4th Central European Symposium on Building Physics (CESBP 2019). Černý, R., Kočí, J. & Kočí, V. (eds.). Prague, Czech Republic: EDP Sciences, p. 1-6 6 p. 02073. (MATEC Web of Conferences, Vol. 282).

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