This investigation shows that ETICS on light weight structures pose no moisture problem in cold and moderate climates when the detailing of joints and openings is well done, i.e. there is no rain water leakage. This holds for all locations investigated. However, if water leakage cannot be excluded completely and therefore the North- American Standard assumptions - penetration of 1% of the driving rain load - are applied this picture changes, making the drying potential an essential feature. The normal ETICS composed of vapour retarding EPS insulation slabs cannot provide much drying towards the exterior and may therefore bear a moisture damage risk for the underlying substrate. The application of a humidity controlled vapour retarder (PA-film) instead of a conventional polyethylene film at the interior side of the building assembly enhances the overall drying potential of the construction by allowing some vapour diffusion towards the interior spaces. But only in warmer locations, like Wilmington in North Carolina or Lisbon, employing such a vapour retarder may be a compensation for small rain water leaks. The best but also most expensive solution would be to replace the expanded polystyrene (EPS) by high density mineral wool insulation slabs in the ETICS.
Alternative ways of solving the rain penetration problem are currently being developed and tested in North- America. Many systems now provide a drainage plane between the substrate and the ETICS and flashing to force the water out at the bottom of the wall. Other systems keep the face seal approach and rely on more sophisticated detailing and flashing. In both cases the long-term performance is still unknown. In order to avoid a repetition of the North-American problems with ETICS on wooden structures, it is important to communicate this issue and possible solutions to the European construction trades. Hygrothermal simulations may help to raise the awareness to the damage risks and the importance of qualified workmanship involved in the application of ETICS especially in cases of high wind driven rain loads.


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Influence of Rain Water Leakage on the Hygrothermal Performance of Exterior Insulation Systems

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