Sash for closing an architectural opening having an inner side and an outer side, comprising: - a transparent element, preferably of a planar shape, suitable to allow the passage of light through the sash, having an inner face and an outer face; - a weight-bearing frame, placed towards the inside, preferably in wood, suitable to support the transparent element and lock it engaging the inner face; - a cover frame, placed towards the outside, preferably in aluminium, fitted on the weight-bearing frame, suitable to protect the latter on the outer side; - a plurality of locking elements attached to the weight-bearing frame and supporting the cover frame; wherein the cover frame comprises upright elements and transversal elements suitable to reciprocally engage one perpendicular to another, wherein the upright element and the transversal element are profiled, having in a central transversal cross-section C or U-shaped, identifying therein respectively an upright cavity and a transversal cavity made to snap-engage with the locking elements, wherein the upright cavity and the transversal cavity engage each other continuously at the angle, wherein the upright element has, at its end, an upright engagement surface and the transversal element has, at its end, a transversal engagement surface angled, for example at 45°, to permit said mutual engagement at the angle between the upright element and transversal element identifying a slot between them; wherein the upright element comprises a cover layer overlying the slot and wherein the transversal element has an outer transversal surface, facing towards the outer side, wherein said outer transversal surface is suitable to rest on the inner side of the cover layer, characterised in that said upright element and said transversal element have a different thickness in such a way as to enable their mutual engagement and, on the side facing the weight-bearing frame, to have the cover frame aligned on a single plane. - a transparent element, preferably of a planar shape, suitable to allow the passage of light through the sash, having an inner face and an outer face; - a weight-bearing frame, placed towards the inside, preferably in wood, suitable to support the transparent element and lock it engaging the inner face; - a cover frame, placed towards the outside, preferably in aluminium, fitted on the weight-bearing frame, suitable to protect the latter on the outer side; - a plurality of locking elements attached to the weight-bearing frame and supporting the cover frame; wherein the cover frame comprises upright elements and transversal elements suitable to reciprocally engage one perpendicular to another, wherein the upright element and the transversal element are profiled, having in a central transversal cross-section C or U-shaped, identifying therein respectively an upright cavity and a transversal cavity made to snap-engage with the locking elements, wherein the upright cavity and the transversal cavity engage each other continuously at the angle, wherein the upright element has, at its end, an upright engagement surface and the transversal element has, at its end, a transversal engagement surface angled, for example at 45°, to permit said mutual engagement at the angle between the upright element and transversal element identifying a slot between them; wherein the upright element comprises a cover layer overlying the slot and wherein the transversal element has an outer transversal surface, facing towards the outer side, wherein said outer transversal surface is suitable to rest on the inner side of the cover layer, characterised in that said upright element and said transversal element have a different thickness in such a way as to enable their mutual engagement and, on the side facing the weight-bearing frame, to have the cover frame aligned on a single plane.