Vapour diffusion

Vapour diffusion within floors of inhabited multi-storey dwellings causes virtually no problems, as long as the temperature on both sides of the supporting structure is similar. However, a new situation arises in inhabited top-floor accommodation underneath lofts which have not been insulated, and in dwellings above basements. Here an expert opinion pursuant to DIN 4108-4 should be obtained. A three-dimensional illustration may become necessary to obtain a clear representation of the interaction between the different substances. We co-operate closely with the Institut für Bauklimatik of theTechnical University of Dresden for the determination of a transparent technological basis.

In internal insulation systems of older timbered ceiling structures, the beam ends become bridges for heat transfer and diffusion. Contrary to the previous prevailing view that everything should be as vapour-tight as possible, it has become apparent that structures that are open to diffusion constitute a better solution. However, the large number of factors of influence in different building structures makes it necessary for every complete building to be considered in isolation.

Temperaturfeld am 11. März mit Calciumsilikatdämmung im Zwischendeckenbereich (Schaubild nicht maßstäblich)
 

Temperature field recorded on 11th March with calcium silicate insulation in the intermediate ceiling area (not to scale) Source: TÜ Dresden, Institut für Bauklimatik

Verlauf des Wassergehalts im Holzbalken auf der Höhe der Außenseite der Zwischensparrendämmung in Abhängigkeit von der Dämmung im Deckenbereich
Distribution of the water content in a timber beam at the level of the outside of the inter-spar-insulation in relation to the insulation in the ceiling area. Source: TÜ Dresden, Institut für Bauklimatik