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

We also [ohne]. but if you have been sitting somewhere, you should definitely ventilate. Manually. Window handle!

Disadvantage and advantage of controlled residential ventilation system are known as far as whether you get mold problems without controlled residential ventilation if you do not ventilate the house about 10 times a day, this is the statement from those who have such systems or the people who build or manufacture them. I know many who live in new buildings (at least Kfw 70), ventilate twice a day and have no mold problems like, for example, @Egon 12 and . (Counterexample to the above statement). My personal opinion: many companies that make money through controlled residential ventilation system create panic and increase the demand for such systems. Those who install/have such systems installed because of fear of mold in new buildings can save their money, unless you have endless money, want to gain more comfort and have no problems with controlled residential ventilation system (e.g. sensitive to partially too dry air). Ventilation should/must be done in any case, whether manually or automatically. Back to the topic of windows, I would definitely choose double-leaf (with 151 cm width, I find guest WC more comfortable with small windows but I will think it over, read opinions and decide later.

Just for the sake of completeness: I wrote about improper ventilation, not that one has to ventilate 10 times a day.

Someone else wrote about airing out 10 times a day. By the way, I also really like the last version. But in general, I am a fan of the look of divided windows.

That was the statement from blaupuma in #8 and coincidentally something a BU almost said to me. On the internet, you can also find the same statements in various discussions.

Here, two years without controlled residential ventilation, everything is great!! and very good air quality thanks to many natural building materials ([oiled wood on floors and furniture], [lime plaster] and [mineral paint]).