The upper and lower sliding windows have more design flexibility in the slenderness ratio of height to width, and the facade appears beautiful and light. The upper and lower window sashes can be divided by different lines. The window frame is simple and the lines are delicate. Ventilation and lighting are equally important without visual obstruction. The upper and lower window sashes can be adjusted according to the ventilation needs. Because they are not casement or sliding, the setting of screens is also relatively easy, and it is also easy to escape in an emergency. If designed as a continuous lifting window, you can fully enjoy natural ventilation. It is another choice for designers between casement windows and sliding windows.