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The Fortochka principle

Fortochka is the name of a very special type of window designed by Rastrelli for the Winter Palace. The window, also known as a Russian window, had many more functions than simply being a piece of framed glass in a hole in the wall.

The window was constructed in accordance with the age-old principle of separating two windows so that there is a space between the two layers of glass. The placing of an opening at the bottom of the outermost window and at the top of the innermost window means that the window can be open for ventilation without the loss of heat and without noise and pollution entering from outside. If a blind is installed in the gap then the Fortochka window can supply maximal solar heat in the cold seasons and screen off dazzling sunlight and excess heat in the summer.

The modern version of Fortochka is widespread in Finland and Russia. And in Denmark we have gradually opened our eyes to the window, which has more functions than standard windows and many advantages: cleaner buildings, insulation against noise and a reduction in heating and ventilation costs. Perhaps the most important is that the multi-functional window is helping to render the installation of air-conditioning superfluous.

The window is known by several different names: third-generation windows, ventilation windows and sound-air windows. Our measurements show a clear, positive effect on the indoor climate. With the Fortochka window the building owner can save much money in an environmentally-sound manner.