Timber frame prefab house: "Coloring" of the outside of the south wall

Hello everyone,

we are currently facing the purchase decision of a prefabricated house in timber frame construction.

A few data points briefly – if anything is missing, please let me know:
- Built in 2001
- End of terrace house
- Diffusion-open wall construction (outside->inside): 7mm mineral plaster, 60mm wood fiber board, 160mm timber frame / "mineral thermal insulation, 15mm OSB board, 12.5mm plasterboard
I do not yet know the exact details of the materials used. U-value according to the construction description 0.17 W/(m² K)
- Partial wall heating installed (I am not sure if this is relevant here).

I have now noticed the "pattern" on the exterior wall (south side), which quite accurately suggests the positions of the timber studs etc. I think the picture in the attachment gives the most insight into the light/dark differences (circular light spots). In my previous internet research, I have only come across the topic of "dowel fastening" of the external insulation.



My specific questions are therefore primarily:
- Where does this pattern come from?
- Are thermal bridges the cause?
- Is this a structural defect?
- What impact does this have on the building fabric?
- Is it to be assumed that the building fabric has already been damaged or that damage will occur in the future?

Thank you very much!

Regards
mawoc

PS: I understand that a remote diagnosis is always difficult. I will probably still commission an expert. Nevertheless, I would find opinions/experiences on the subject very helpful.

I assume that small, localized, linear thermal bridges are present at these points. This causes the facade to be slightly warmer here than the rest, so that moisture from dew, etc. evaporates more quickly and therefore fewer algae are present than on the rest of the facade.

This is not serious, it only means a cosmetic defect.

Regards