ᐅ White spots on wood fiberboards above the rafters

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

This is definitely mold. Do not ignore it and look for the cause—there is something leaking or not sealed properly.

tomtom79 schrieb:

That is definitely mold. Don’t ignore it—there is a leak somewhere.

My amateur guess is also mold. Since you don’t seem to be a professional in this matter, I would get help to locate any leak and have it checked whether the cause is due to poor workmanship during construction.

After 12 years and still seeing white mold, I suspect that something might have been changed later on, perhaps the addition of photovoltaic panels or a defective roof hatch, etc.

Nothing has been changed. I am surprised that the infestation is spread over the entire, rather lower half of the roof. If there were a leak in the vapor barrier, wouldn’t the infestation be more localized? The vapor barrier was properly sealed and has no holes.

Thanks by the way for your answers