Abstract: The invention relates to a system for opening and closing a window aperture, the system comprising: a moveable window panel; a pulley assembly coupled to the moveable window panel; a counterweight; and a pulley actuation mechanism. The moveable panel is heavier than the counterweight, the latter being attached to a first lateral side of the moveable panel via a first part of the pulley assembly. The pulley actuation mechanism is attached to an opposite lateral side of the moveable panel via a second part of the pulley assembly.