Diffusion foil on roof, adhesive spots are leaking!

Hello everyone,

first of all, thank you very much for your contributions!!

The lower half of the roof is indeed inhabited/heated.
As mentioned, it is a diffusion foil that is waterproof but allows water vapor to pass through. Why should there be mold?

The actual question is:
Was the foil professionally installed?
Doesn't it have to be laid crosswise on the roof, overlapping from bottom to top?
Should a special adhesive tape have been used here?
Is this a hidden defect that carries a 30-year warranty?

Yes, right... at the moment I don’t have an acute problem, but normally the diffusion foil should be considered a second line of defense in case the first fails, for example if a roof tile becomes leaky or something like that, which can happen.

Regards
ariovist8

Hello,

so, on the inside of the construction is the airtightness layer. This is responsible for keeping water vapor out of the construction. The foil must be diffusion-tight.
On the outside of the construction is the windproof layer. This is responsible, among other things, for keeping out the wind (hence the name [Bratkartoffeln]) and possibly draining water entering under the roof covering. This foil must be diffusion-open. If this foil is now damaged, then the construction is faulty.
The question now is: Has it always been faulty? Or was everything correctly installed at some point? And has the adhesive bond failed due to lack of quality (it’s already been 14 years after all)?

Who even installs the underlay membrane parallel to the rafters?

Regards

Hello

If the [Unterspannbahn] is installed vertically from the eaves to the ridge, it is a defect. If it were installed parallel to the eaves with an overlap, the joints would not necessarily have to be glued. If they are glued and the adhesive tape comes loose over the years, that is not a problem. Because due to the overlap, the [Unterdach] is still water-repellent.

Regards Sven