ᐅ White spots on wood fiberboards above the rafters

Created on: 2 Dec 2021 16:14
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Wolfgang2002
Hello everyone,
we have been living in our low-energy house for 12 years. For the past three days, there has been a musty smell in a room facing north. I just climbed onto the roof and checked the wood fiberboard under the tiles. There are white spots everywhere, and I don’t know what they are. Hopefully, it’s not mold.
The roof is constructed as follows:
Drywall on batten framework
Vapor retarder
Rafters
Insulation between the rafters with space for ventilation
On top of that, wood fiberboard
And finally a “membrane”
Battens
Concrete tiles
Can anyone tell me what these spots might be?

Thank you and best regards,
Wolfgang2002

Close-up of light skin with spots under dark gray fabric; finger lifting fabric.
Patricck2 Dec 2021 21:52
I’m just wondering why it’s so easy to look underneath the membrane?
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Wolfgang2002
3 Dec 2021 11:46
Patricck schrieb:

I’m just wondering why it’s so easy to look underneath the membrane?
I cut it open and then resealed it afterwards. This is the membrane between the roof tiles and the wood fiberboard.
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Kati2022
15 Dec 2021 18:07
Wolfgang2002 schrieb:

<I cut it open and then glued it back together. This is the membrane between the roof tiles and the wood fiber board.
I’m interested in this as well.
We are currently planning our roof construction for a KfW55 house. Our energy consultant recommended 22cm (9 inches) rafters with insulation between the rafters plus 6cm (2.5 inches) wood fiber insulation above the rafters. He said there is NO membrane between the wood fiber boards and the roof tiles... The wood boards serve as both the airtight layer and are vapor-permeable at the same time. Hmm...???
You have a membrane... maybe that’s the reason?
What is the correct approach now?
Membrane yes or no?