The formerly applied box or Swedish windows due to their construction with the passage of time were subject to warping, gaps appeared through which the expensive heat escaped. Equally the application of single panes in windows assured feeble thermal insulation, and the application of double windows hindered window cleaning.

External door per definition mean a moveable element which closes the opening leading to the building interior. However, when we look at the element from deeper perspective, we can boldly say that it is the showcase of our house. External door very often becomes the main element which forms the whole building elevation, gives it the individual character and specific spirituality. Many times they also reflect the character of the very owners. Many different materials, inter alia PVC, aluminium, steel or wood are applied for production of external door.

In the recent years, together with the development of modern construction the tendency for opening housing spaces to gardens and terraces appeared. Traditionally applied single or double leaf balcony solutions appeared to be insufficient – sudden increase of the openings caused the increase of weight of a single leaf often exceeding the technical possibilities for such a window manufacturing. Additional difficulty in free moving was the application of a threshold in the types of windows.