That was interesting, thanks.

But you might be pleased that the most modern system at least in Finland actually has little of the same features than the romans had. If you look at the same membrane I posted earlier, it has little knobs that hold it little bit away from the wall:

https://monosilla.files.wordpress.com/2014/11/screenshot-201...

I don't know the English word for it. It's not perfect, but lot better than couple decades ago. They used to paint the concrete with tar. This "patolevy" is cheaper, easier to install and allows little bit of ventilation.