I had a house I purchased that had previous residents that were very heavy smokers. Everything in the house was covered in a yellow brown film. Steps I had to take to remove the smell.
All hard surfaces were washed twice with TSP in hot water. This was necessary because the yellow gunk was so thick that the first washing just could not get it all off. ...
3 layers of pegboard (pierced hardboard), internal surfaces painted black, with the middle layer offset, and spacers between the layers. This should provide little or no straight path for light, but allow ventilation.
"Dehumidifying cool areas" is a serious trick
It's a common problem in England too, where it's called "the damp".
The crux of the problem is warmer air can hold more water than cool air. 100% humidity at 10C may be 30% humidity at 25C. That's how air conditioners and dehumidifiers cool the air. If they chill air to 10C, it can't hold much water, so ...
Sick building syndrome is common and comes in many forms. Here’s an article that explains it better:
Also, it could be glue “outgassing”.
Formaldehyde (in glue) out-gasses for several months after it it is made into building materials. Products like particle board in countertops, OSB board in ...
Consider a combination of options:
Awning over the window. This keeps sunlight from striking the window at least at mid day. The wider the awning is, the more time it shades the window.
Exterior bamboo rollup blind. This will block about 90% of the light. If you mount it so that it stands a few inches out from the wall, it won't impede the air much at ...
Install a room to room transfer fan in the wall at the bottom of one side of your wall, and install an intake louver at the top of the other side of the wall in the same stud cavity. The reason for the high/low setup is to help reduce noise from transferring between rooms.
An example product that would work for this is here: Tjernlund-AS1-AireShare-Room-to-...
Have you considered just increasing the gap under the door to 1cm or 2cm and putting a fan to extract air from the room into the roof space?
You would only need to have a small fan - even a 4" fan from a computer power supply (although there are quieter ones, or reduce the voltage a bit) will create probably sufficient air movement.
Short of replacing your window with a duct with several turns, lined with sound baffles, you aren't going to get quiet.
Human ear is amazingly sensitive. 30 db is a very quiet country side. Flies buzzing, birds chirping. Office is about 70 db 40 db difference doesn't sound like much, but it's a log scale. That office is a thousand times noisier.
3 db ...