ᐅ Condensation Formation

Hello and good evening. I have a general question... If I have drywall (gypsum board) on the walls in the attic... and let's say some people are up there, or condensation somehow forms under the panels... then, if the vapor barrier between the foil and the drywall is airtight, the moisture will stay there and eventually evaporate, right? But if it were leaking somewhere, the condensate would pass through the foil into the insulation. However, since the breathable underlay membrane is diffusion-open, it could escape to the outside above it, correct?

Condensate (liquid water) forms when moist air is cooled below the dew point or when it comes into contact with a surface whose temperature is below the dew point (compare to glasses fogging up in winter). The vapor barrier prevents water vapor (!) from the humid indoor air from entering the insulation, where it would then condense due to the lower temperature present somewhere within the insulation.

Condensed water on or beneath drywall boards will run down the boards; it will not pass through the vapor barrier, as it does not allow water to pass. Eventually, this water will evaporate, yes.

In the case of a leaky vapor barrier on a sloping roof, liquid water would have to overcome gravity. This is conceivable through capillary action, but in my opinion, it is unlikely under realistic conditions.

However, through leaks in the vapor barrier, moist—relatively warm—air from the interior can enter the insulation. There, under certain conditions (cold insulation), the water vapor could then condense.

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However, due to leaks in the vapor barrier, moist — relatively warm — air from the interior can enter the insulation. This could then potentially cause condensation of water vapor in the insulation (which is cold).

That was my misconception. Thank you 🙂