Healthy Building - What is important?

And what was so pleasant about it? Or more pleasant than in other houses? Or even more pleasant than outside? Or was it perhaps just the wood look? Or the resin that evaporates from the wood?

That is difficult to describe, I think. It simply wasn’t humid or dry. Sometimes, when I enter a store, I immediately notice that the indoor climate is unpleasant. I can’t describe it well, but I have a "feeling" of how a room feels.

A wall that actually allowed free air exchange from inside to outside and vice versa would be a building physics disaster

No, this wall just has an open window.

Ah, measurable, then bring on the measured numbers.

Do you read here, the book is also used at universities.

Are you reading here, the book is also used at universities.
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Please finally be specific.
Posting a randomly selected book cover does not support a single one of your statements.

Every time you don’t know something, others are supposed to read and google.
I am already quite sure that your comparison of walls with the lung does not withstand any scientific examination!

So, let’s get to the point, how much CO2 passes through your wooden walls?

I have solid wood walls (whether anyone notices a different indoor climate there) but no wood look. Diffusion-open walls and ventilation system. It was recommended that way because of air exchange. And I notice the difference between open windows, controlled residential ventilation, or no ventilation.

There is no direct preferred direction of diffusion. The concentration gradient is decisive. Therefore, CO2 would diffuse out and O2 would diffuse into the house. N2 does nothing because inside and outside are the same. CO2 is a larger molecule than O2 and therefore diffuses somewhat less well but almost negligibly. Almost nothing is absolutely airtight, not even a wall. Therefore, diffusion exchange is measurable but also negligibly small.

Even the bad EPS is not "tight". It is just less diffusion-permeable. Therefore, anyone can advertise with this property. Absolutely misleading