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Moisture in Constructions with Loose-Fill Insulation and no Vapour Barrier
KTH, Superseded Departments (pre-2005), Building Sciences and Engineering.
KTH, Superseded Departments (pre-2005), Building Sciences and Engineering.ORCID iD: 0000-0003-0615-4505
1999 (English)In: Nordic Journal of Building Physics, Vol. 2Article in journal (Refereed) Published
Abstract [en]

Out of concern for the environment, the traditional polyethylene vapour barrier in lightweight constructions has sometimes been replaced with more diffusion open materials, such as polypropylene fabric. In order to evaluate how this may affect the risk of condensation in the constructions, in-situ measurements of the moisture content and temperature in the walls, roofs and floors of three houses have been conducted. Furthermore, the measurements have been used to establish a model that can be used to predict the moisture performance for design moisture supply loads. Measurements of moisture content and temperature in the outermost part of the insulation of the constructions have been carried out every three weeks over a two-year period, during which the indoor temperature and relative humidity were continuously registered. Based on indoor climatic data as well as information from a nearby weather station, the moisture conditions have been calculated using a one-dimensional transient diffusion model that takes into account the sorption properties of the materials.

The results of the measurements indicate that for the low moisture supply loads in the three houses there is no immediate risk of moisture damage. The results of the simulations show good correlation with measurements for the walls and a floor. The calculation model was therefore used to simulate the conditions for a design moisture supply of 2 and 4 g/m^{3} using a reference climate for Stockholm from the literature. The results show that even for the lower design value, moisture would accumulate and condense in the wall construction. Since high relative humidity would for long periods of time coincide with temperatures feasible for mould growth, the wall construction is not to be recommended. A similar simulation of the piled floor construction shows that even for moderate moisture supply loads the risk for condensation is high. A correlation for the roof construction could not be achieved without adjusting parameters and therefore the model was not considered valid for the roof. There are strong indications that this is due to ongoing settling of the loose fill insulation in the roof construction, since no evidence of convection could be found from the measurement results.

Place, publisher, year, edition, pages
1999. Vol. 2
Keywords [en]
Vapour barrier, condensation, moisture measurements, transient diffusion model
National Category
Building Technologies
Identifiers
URN: urn:nbn:se:kth:diva-13288OAI: oai:DiVA.org:kth-13288DiVA, id: diva2:323263
Note

QC 20100610

Available from: 2010-06-10 Created: 2010-06-10 Last updated: 2019-10-25Bibliographically approved
In thesis
1. Alternative methods for analysing moisture transport in buildings: Utilisation of tracer gas and natural stable isotopes
Open this publication in new window or tab >>Alternative methods for analysing moisture transport in buildings: Utilisation of tracer gas and natural stable isotopes
2003 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

New methods, based on tracer gas measurements and isotopicanalysis can be used to evaluate the moisture properties ofbuilding materials and provide the means for forensic analysisof the origins and history of excessive water in buildings, theimmediate practical consequences of which will be the abilityto improve the moisture performance of constructions.

It is shown, in theory and through measurements how thewater vapour permeability of porous building materials can witha good degree of accuracy be estimated with tracer gasmeasurements that provide an efficient alternative to the cupmethod. Complementary measurements may be carried out in orderto evaluate the contribution of surface diffusion and theeventual enhancing effects of moisture content on the diffusioncoefficient. The Random Hopping Model is used to illustrate howthe surface diffusion coefficient depends on the amountadsorbed and the activation energy of migration that can beevaluated from the sorption isotherms.

It is explained how the abundance ratios of two of the mostordinary isotopes of hydrogen and oxygen in water can be usedto determine its history. These isotopes are stable and givethe water a distinct signature that can be used to reveal itssource as shown in a case study. In a contrary manner themeasured isotopic separation can be used to determine therelevance of different transport processes and reactions. It isof central importance that not only does the magnitude ofisotopic separation for the reactions vary for deuterium andoxygen-18 but even the ratio thereof. One of the challenges hasbeen to construct an experimental method for retrieving samplesof water for comparison.

Furthermore this thesis includes an evaluation of a new typeof a light weight construction with loose-fill cellulose fibre,in which the conventional polyethylene vapour barrier has beenreplaced with polypropylene fabric. With a verified model ithas been investigated how the construction would perform fordifferent internal moisture loads and reference climate fromthe literature. The results suggest that this type ofconstruction is not to be recommended.

KEYWORDS:tracer gas, water vapour permeability,diffusion, surface diffusion, isotopic analysis, deuterium,oxygen-18, fractionation, vapour barrier, transient numericalmodelling of diffusion.

Place, publisher, year, edition, pages
Stockholm: KTH, 2003. p. xii, 57
Series
Trita-BYT ; 191
Keywords
tracer gas, water vapour permeability, diffusion, surface diffusion, isotopic analysis, deuterium, oxygen-18, fractionation, vapour barrier, transient numerical modelling of diffusion
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-3509 (URN)
Public defence
2003-05-09, 00:00
Note
QC 20100611Available from: 2003-04-28 Created: 2003-04-28 Last updated: 2010-06-11Bibliographically approved

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