Which wall structure is meaningfully vapor-permeable?

Either controlled residential ventilation with heat recovery

And what are decentralized fans? Also a controlled residential ventilation with HRV. Instead of two large holes in the facade, you then get a few small ones. Neither special thermal bridges nor poor insulation of the devices. These are basically the same devices as in a "large" central system, just smaller. Of course, the central controlled residential ventilation is more elegant, but also much more expensive. By the way, a window rebate is nothing more than a permanently tilted-open window. I consider THAT a disaster. But it is dirt cheap.

I personally think decentralized fans are worthless. Either controlled residential ventilation with heat recovery or window rebate.

Controlled residential ventilation with heat recovery is of course only suitable centrally; conversely, controlled residential ventilation centrally only makes sense if you want to include all or the majority of rooms in the controlled residential ventilation. Controlled residential ventilation only for "selected" rooms makes decentralized more commercially reasonable, but then only without heat recovery. A well-known house provider (Kern) has, to my knowledge, a preference for decentralized controlled residential ventilation – probably because it is more economical with the formwork block system construction method.

For me, the decentralized option would be a no-go solely because of the Fassendoptik.

For me, the decentralized option is a no-go alone because of the façade optics.

I always think the same when I see a façade featuring ventilation openings...

If you're already replacing the windows during a renovation, integrated window ventilation with heat recovery could also be a solution, right? You can virtually not see them.

Controlled residential ventilation with heat recovery is of course only suitable centrally;

May I ask why?

integrated window ventilation with heat recovery might be a solution or not?

What is that? Integrated with heat recovery was unknown to me so far. The heat exchanger + technology takes up a lot of space. I only know decentralized with ventilation openings outside in the reveal.

May I ask why?

The process of heat recovery is technically much less efficiently implementable in every single-room mini-controlled residential ventilation unit; I don't even know if the manufacturers themselves don't even see it that way and only offer heat recovery in central systems at all.