Abstract: The sliding sash is supported at a guide rail by a sash portion projecting from the floor in a vertical plane and a sash portion ascending in an inclined plane relative to the inside adjoins an additional tipper sash portion which projects up in the vertical plane and is set back. Every sash portion is formed by a section bar arm receiving a glass pane. The upper sash portion is guided at a ceiling rail with two running paths which are arranged at a distance from one another and parallel to one another. In order to secure this guide relative to loading by wind and/or snow, each running path is formed of two inclined guide paths of a web head of the ceiling rail, this web head having a triangular cross section, and support rollers which are supported at an inclination run on the guide paths of every web head at a roller holder which is fastened to the terminating section bar of the upper sash portion.