Question regarding assessing condensation problems in hydrophobic mineral fiber

[WEI LI]

Hi experts,

I am modeling a roof system comprised of the following layers, from the outermost to the innermost: metal deck, ventilated cavity, underlayer, PIR insulation coated with aluminum facers, and metal deck.

Is it necessary to examine the amount of water content in the outer 1 cm of the PIR insulation, using the method illustrated in the report "How to Assess Condensation Problems in Hydrophobic Mineral Fiber"?

My concern is that if the amount of water content exceeds the critical value (in this case, the measured water absorption level of PIR), the water content would still be constrained by the aluminum facers, and no condensation run-off would occur.

Am I mistaken? Thank you.

[WEI LI]

I will be very grateful if someone can give me some clues or comments. Thank you.

[Christian Bludau]

Dear Wei Li,
as you use PIR insulation and not fiber insulation there will be no direct formation of dew water in the outer centimeter and if there some water accumulates, it will not be able to run off, as it is in the pores. So no, you do not have to access the PIR like a fiber insulation.

I would check the water content (a good unit to compare water in insulation materials is percent per volume) and see, if it reaches values which will lead to an increase of the thermal conductivity. This happens at about 1-2 percent per volume - you can see that in your materials thermal conductivity, moisture dependent curve.

Maybe also have a look in the WUFI Pro program help -> Appendix -> Assessment Criteria

Best regards
Christian