Russian 'Fortochka' windows provide ventilation as well as insulation. They were developed for the Winter Palace in Saint Petersburg in 1754 by the Italian architect Bartolomeo Rastrelli.
The Russian 'Fortochka' window, also known as a ventilation window, is a double window built together as a single unit. The bottom sash in the outer window and the top sash in the inner window are operable. Besides its high insulating properties, the construction also minimises the amount of heat lost during ventilation, as fresh air is warmed up as it enters. The construction also works well for sound protection.