Carbon Dioxide Permeability of Cellulose-Insulated Wall Structures

T. Niemelä, J. Vinha, R. Lindberg

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    Abstract

    A study was conducted at Tampere University of Technology, Laboratory of Structural Engineering in 1995 where the diffusion of carbon dioxide through different building materials, finishes and entire external wall structures was examined. Test equipment consisting of a test chamber and different types of measuring apparatus was developed for the study. The tested material or structure was inserted in the opening of the chamber and sealed. Then a carbon dioxide content of 1 percent was created within the chamber for the test. Tests measured the reduction in the flow of carbon dioxide through the subject material or structure to indoor air over a certain period of time. The results of measurements were used to determine the carbon dioxide permeabilities of materials and the carbon dioxide resistance of structures. Various surveys modelling the carbon dioxide balance of a building’s indoor air were conducted using the measured values. The surveys took into consideration the diffusion of carbon dioxide through the wall structure. Test results indicated that the carbon dioxide permeabilities of building materials correlate closely with the water vapour permeabilities and diffusion through air indicated by other studies. Thus, the more permeable a material is to carbon dioxide, the more permeable it is to water vapour. Based on the modelling surveys, it can be stated that gas-permeable (breathable) wall structures lower the carbon dioxide content of indoor air, but do not reduce the need for ventilation. In a well-ventilated building permeable walls have no practical significance in improving indoor air quality. On the other hand, permeable structures can alleviate the detrimental effects of temporarily high carbon dioxide contents. This study examined indoor air quality using carbon dioxide. Yet, the quality of indoor air is generally determined by other gases which people find unpleasant at much lower concentrations than carbon dioxide. The removal of these impurities through structures would call for even more permeable wall structures which is impracticable. This also emphasizes the significance of efficient and properly planned ventilation in buildings. In order that external wall structures could have an impact on the carbon dioxide content of indoor air, the materials of the structures should be as permeable (allowing diffusion) as possible. Yet, this also allows more water vapour to pass through the structures which makes them more at-risk for condensation in autumn and winter. The risk of moulding also increases. Thus, use of structures that are too permeable on the inside is not recommended.
    Translated title of the contributionCarbon Dioxide Permeability of Cellulose-Insulated Wall Structures
    Original languageEnglish
    PublisherTampere University of Technology
    Number of pages55
    Publication statusPublished - 2000
    Publication typeD4 Published development or research report or study

    Publication series

    NameTampere University of Technology, Structural Engineering, Publication
    PublisherTampere University of Technology
    No.104

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