US Patent 6840009 Sliding window structure with sash guiding tracks

A sliding double hung window structure allows a window opening to be fully exposed to the external environment in an open position, with casements or windows being stored out of sight, and not in the opening. The window structure includes two casements or sashes balanced by suspended counterweights and guided by pins in guiding grooves in the two vertical sides of a frame of the window structure. In the closed position, the casements are located in the same plane, one on top of the other. When fully opened, a breast cavity under the window opening receives the two casements. The guiding grooves include guiding grooves in the window opening and in the breast cavity.