A dual-function roof window with sash mounting assembly comprising - a sash with glazing unit and side member of the sash frame - a window frame - where said dual-function roof window is arranged to be opened in a pivoting function, that is by rotation of the sash around a horizontal axis located slightly above half the height of the window, and/or opened in the tilting function, that is by rotation of the sash around a horizontal axis located at the top of the window, and said sash mounting assembly comprising - pivoting hinges and tilting hinges, - two intermediate arms, located on the outside of the sash on its right and left side, wherein upper ends of the said arms are connected by the tilting hinges to the window frame, and their lower ends are connected by two pivoting hinges to the window sash, where in each of the pivoting hinges, the first hinge sub-assembly comprises an arch-shaped guide attachec in the intermediate arm, and the other hinge sub-assembly comprises an arch-shaped slider, arranged to be moved along the arch-shaped guide of the first sub-assembly, and comprises a plate for attaching the other sub-assembly to the lateral plane of the window sash, referred to as the 'slider plate', whereas the arch-shaped slider is connected to the slider plate by means of the axis which is arranged to allow for additional rotation the sash after sliding the arched-shaped slider out of the arched-shaped guide to the forward-most position, characterised in that - each pivoting hinge comprises two planes (10, 11) which are adjacent to the arched-shaped slider sides from the side of the window sash and from the outside of the sash and each pivoting hinge is located on a section of the arch-shaped slider which is arranged to be moved along the arch-shaped guide, and the slider plate comprises a spacer offset, from which protrudes the axis on which the arch-shaped slider is mounted such that said planes (10, 11) referred to respectively as the 'inner plane of motion', and the 'outer plane of motion', are located on both sides of the plane perpendicular to the axis of rotation of the sash, determined by the geometrical centre of the intermediate arm's main cross-section in all its positions, wherein the spacer offset is monolithic with the slider plate. - a sash with glazing unit and side member of the sash frame - a window frame - where said dual-function roof window is arranged to be opened in a pivoting function, that is by rotation of the sash around a horizontal axis located slightly above half the height of the window, and/or opened in the tilting function, that is by rotation of the sash around a horizontal axis located at the top of the window, and said sash mounting assembly comprising - pivoting hinges and tilting hinges, - two intermediate arms, located on the outside of the sash on its right and left side, wherein upper ends of the said arms are connected by the tilting hinges to the window frame, and their lower ends are connected by two pivoting hinges to the window sash, where in each of the pivoting hinges, the first hinge sub-assembly comprises an arch-shaped guide attachec in the intermediate arm, and the other hinge sub-assembly comprises an arch-shaped slider, arranged to be moved along the arch-shaped guide of the first sub-assembly, and comprises a plate for attaching the other sub-assembly to the lateral plane of the window sash, referred to as the 'slider plate', whereas the arch-shaped slider is connected to the slider plate by means of the axis which is arranged to allow for additional rotation the sash after sliding the arched-shaped slider out of the arched-shaped guide to the forward-most position, - each pivoting hinge comprises two planes (10, 11) which are adjacent to the arched-shaped slider sides from the side of the window sash and from the outside of the sash and each pivoting hinge is located on a section of the arch-shaped slider which is arranged to be moved along the arch-shaped guide, and the slider plate comprises a spacer offset, from which protrudes the axis on which the arch-shaped slider is mounted such that said planes (10, 11) referred to respectively as the 'inner plane of motion', and the 'outer plane of motion', are located on both sides of the plane perpendicular to the axis of rotation of the sash, determined by the geometrical centre of the intermediate arm's main cross-section in all its positions, wherein the spacer offset is monolithic with the slider plate.