As part of a course in Hygrothermal Risk Assessment (taught by Joseph Little of TU Dublin) Oliver carried out an assessment of a proposed “hybrid green roof” in County Limerick Ireland.

The report concluded that the proposed hybrid inverted roofs are problematic primarily because they have poor drying capacity and as such are not resilient to various anticipated or unanticipated inputs of liquid moisture. Even with the addition of a VARA plus variable diffusion VCL, which did improve the dynamically modelled moisture performance of the roof, the OSB deck, which remains fairly cold during the winter, is unlikely to dry out sufficiently given potential inputs of moisture such as infiltration. The roofs do not appear to be resilient to potential sources of moisture such as increased internal occupancy and ingress of rainwater due to a poorly fitted “vapour permeable waterproof isolating layer” above the XPS.

The report can be downloaded here but is provided without any warranty to its correctness. If you wish to obtain the appendicies which detail the full WUFI modelling undertaken, please contact me.