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Wärmedämm-Verbundsysteme (WDVS) für die Anwendung auf Außenwänden im Holzbau werden national durch allgemeine bauaufsichtliche Zulassungen geregelt. Im Zuge der Zulassungserteilung muss der dauerhaft wirksame Witterungsschutz der Holzkonstruktion durch das WDVS nachgewiesen werden. Dies kann im Wandprüfstand durch die Messung von Holzfeuchten sowie Temperaturen und rel. Luftfeuchten in verschiedenen Bereichen der Konstruktion bei hygrothermischer Belastung nach ETAG 004 erfolgen. Hersteller von WDVS sind bestrebt, den Zeit- und Kostenaufwand für solche Prüfungen zu optimieren, indem aus der Vielzahl der zur Verfügung stehenden Putze und Dämmstoffe nur die ungünstigsten Kombinationen geprüft werden. Die Entscheidung über die ungünstigste Variante wird meistens anhand einzelner Kriterien, wie Wasserdampfdurchlässigkeit des Putzes, getroffen. Die hygrothermischen Simulationen haben jedoch gezeigt, dass bei Einbeziehung verschiedener Randbedingungen die ungünstigste Variante nicht immer erwartungsgemäß ausfällt. Der Beitrag zeigt beispielhaft, wie und unter welchen Voraussetzungen Simulationsberechnungen zu einer sicheren Einschätzung des hygrothermischen Verhaltens der verschiedenen Varianten einer Wandkonstruktion führen.

ETICS in timber frame constructions - optimised proof of the permanent weather protection through a combination of measurements on the test bench and hygrothermal simulations.
External thermal composite systems with rendering (ETICS) for use on exterior walls in timber frame constructions are regulated nationally through general building inspectorate approvals. In the course of issuing the approval, the permanently effective weather protection of the timber construction must be proven by the external thermal composite system. This can be carried out on the test bench for walls by measuring the timber moisture contents as well as temperatures and rel. humidities in various areas of the construction with a hygrothermal load pursuant to ETAG 004. Manufacturers of ETICS strive to optimise the time and costs of such tests by only testing the most unfavourable combination of renderings and insulating materials from the wide variety that are available. The decision about the most unfavourable variant is usually taken on the basis of only a few criteria such as the water vapour permeability of the rendering. However, hygrothermal simulations have shown that if various marginal conditions are taken into account, the most unfavourable variant is not always as expected. The article shows by way of example how and under which conditions simulation calculations lead to a more reliable estimate of the hygrothermal behaviour of the different variants of a wall construction.
 
Source:     Bauphysik 38 (2016), No. 3
 
Page/s:     135-146
 
Language of Publication:     German



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