A roof window, particularly for installation in an inclined roof surface, comprising a primary frame, at least one secondary frame (2, 3), such as a sash and/or an intermediate frame, and a lifting device including a lifting arm inserted between the primary frame and the at least one secondary frame (2, 3), a sledge system and a coupling mechanism, the lifting arm having a first end rotatably connected with said sledge system slidably connected with the primary frame in a sledge guidance and a second end rotatably connected with the at least one secondary frame, the lifting device furthermore including a spring assembly configured to be coupled to the sledge system and in turn the first end of the lifting arm by means of said coupling mechanism, such that the spring assembly is able to assume an uncoupled condition and a coupled condition relative to the sledge system, the spring assembly comprising a main spring system and a buffer spring system inserted between the main spring system and the lifting device, wherein the spring assembly further comprises a spring casing, wherein said spring casing further includes at least one recess for receiving an adjustment plate, characterised in that the buffer spring system comprises an outer spring and an inner spring of substantially identical pre-defined lengths, and that the inner spring is at least partially accommodated inside the outer spring so that the axes of the respective springs extend substantially coaxially, wherein the outer spring and the inner spring of the buffer spring system have mutually different spring constants, wherein the outer spring and the inner spring of the buffer spring system have mutually opposite thread directions, wherein the spring assembly further comprises at least one spring plug (283, 284) configured to be in contact with the respective end of the inner spring of the buffer spring system in the mounted condition, and wherein said at least one spring plug (283, 284) is provided with friction-increasing means at the surface configured to be in contact with the respective end of the inner spring of the buffer spring system. a primary frame, at least one secondary frame (2, 3), such as a sash and/or an intermediate frame, and a lifting device including a lifting arm inserted between the primary frame and the at least one secondary frame (2, 3), a sledge system and a coupling mechanism, the lifting arm having a first end rotatably connected with said sledge system slidably connected with the primary frame in a sledge guidance and a second end rotatably connected with the at least one secondary frame, the lifting device furthermore including a spring assembly configured to be coupled to the sledge system and in turn the first end of the lifting arm by means of said coupling mechanism, such that the spring assembly is able to assume an uncoupled condition and a coupled condition relative to the sledge system, the spring assembly comprising a main spring system and a buffer spring system inserted between the main spring system and the lifting device, wherein the spring assembly further comprises a spring casing, wherein said spring casing further includes at least one recess for receiving an adjustment plate, characterised in that the buffer spring system comprises an outer spring and an inner spring of substantially identical pre-defined lengths, and that the inner spring is at least partially accommodated inside the outer spring so that the axes of the respective springs extend substantially coaxially, wherein the outer spring and the inner spring of the buffer spring system have mutually different spring constants, wherein the outer spring and the inner spring of the buffer spring system have mutually opposite thread directions, wherein the spring assembly further comprises at least one spring plug (283, 284) configured to be in contact with the respective end of the inner spring of the buffer spring system in the mounted condition, and wherein said at least one spring plug (283, 284) is provided with friction-increasing means at the surface configured to be in contact with the respective end of the inner spring of the buffer spring system.