Windows & window size: what to choose? Double-leaf windows?

For 2 years and 3 months without a ventilation system... airing once in the morning for 10-15 minutes. No mold or anything similar...

Blower Door Test resulted in 0.3 back then...

For 2 years and 3 months without a ventilation system... airing once in the morning for 10-15 minutes. No mold or anything similar...

Blower Door Test was 0.3 back then...

Here, two years without controlled residential ventilation, all good!!
and very good air quality due to many natural building materials (oiled wood on floors and furniture, lime plaster and mineral paint).

One question: (actually belongs to another category in the forum but fits well with this discussion)
, , you haven’t installed a ventilation system. Do you have exhaust fans in the bathroom, WC and utility room?
Our contact person from the construction company, who himself worked for years as an energy consultant, told us that without a controlled residential ventilation system and with proper window ventilation, we will not have mold problems (I believe that too). He also said that in the bathroom, guest WC and utility room (with washing machine, condenser dryer and utility sink, without windows but with a side entrance door) we really do not need exhaust fans.
(Our bathroom will only have four corners, so no niche or shower enclosure, but a curtain).
Do you or maybe someone else have experience with this?

Have been inside since the end of December, without controlled residential ventilation. There are fans in the bathroom and the utility room, but we also hang (a lot of) laundry to dry there. In the bathroom, we would probably manage without a fan by ventilating with the window, the fan in the utility room runs more often. No idea if it is absolutely necessary, but it certainly contributes to my peace of mind that there is a fan there.

One question: (actually belongs to another category in the forum but fits well with this discussion) , , you did not install a ventilation system. Do you have exhaust fans in the bathroom, WC, and utility room?

Do you or maybe someone else have experience with that?

No...nothing of the sort installed...all ventilation only through the windows.

We also dry our clothes in the utility room (about 11 sqm)...there I also ventilate more frequently.

But even there no mold or mildew stains.

If everything in new buildings has been constructed correctly, mold is rare anyway. It then occurs in cold spots that fall below the dew point. Mainly, it is about air quality. And usually, a controlled residential ventilation system ends up with a maximum of plus or minus zero. However, it is supposed to provide a great increase in comfort. Everyone I know would never go without it again. By the way, everyone with an exhaust fan also has active ventilation. Only it is unregulated.

Hi, one more question about the window size.

We also want two-wing windows now.

What size is good?

Is there anyone here who says my two-wing window is too big in retrospect?

We are planning rather large two-wing windows and don’t know if it might look too big.

Attached are our planned windows as an example (window is not final yet, will still be adjusted, faucet problem will also be resolved, for now it’s just about the window size in relation to the room)