Very high humidity in all rooms

Clearly a thermal bridge problem. The windows are no longer the coldest spot but the wall. Moreover, the new ones probably seal tighter than the old ones, so there is no longer any forced ventilation. -> Condensation at the coldest spots of the most frequently used rooms. Ergo: ventilate more (twice a day is not enough). Or heat more or actively dehumidify.

Hi, the walls were not renovated.

The classic: new windows with old, still uninsulated walls. The uninsulated walls are colder than the new windows, and moisture thus settles on the walls and causes mold. The north wall will be the coldest, but this applies to all exterior walls. Due to the new windows, there is also no longer any normal air exchange. This can be retrofitted with window seal ventilators. You should definitely take measures regarding insulation.

Thank you very much for the feedback.

As mentioned, we are considering blown-in insulation. For this, I have calculated the structure with Ubakus (attached) and see that condensation accumulates in the insulation. I am afraid of making it worse. Insulation on the façade would currently not be financially feasible.

Has anyone had experience with blown-in insulation and can share their experiences?

Regards Andre

Insulation on the facade is currently not financially feasible.

Then only blown-in insulation remains and raising the room temperature to 22-23 degrees, and keeping furniture away from the exterior walls.

Then only blown-in insulation and increasing the room temperature to 22-23 degrees remain, and keeping distance with the furniture from the exterior walls.

Thank you for the information. I have uploaded it as pictures.

Retrofitting decentralized fans with heat recovery. Window rebates are rubbish and really do not even deserve to be called a makeshift solution. Why install new, well-insulated and airtight windows only to make the nice new window drafty again with a rebate vent?