The building envelope element comprises translucent hollow glass bricks (22) that are filled with a phase shift material (24) and consist of an interior wall (2) that is designed to be installed on an interior side of the building, an exterior glazing (3) designed to be installed on an exterior side of the building, and an insulating wall (5) that consists of a granular silica aerogel/xerogel and is interposed between the interior wall and the external glazing. The phase shift material is opaque when it is present in a solid state, and is translucent when it is present in a liquid state.; The building envelope element comprises translucent hollow glass bricks (22) that are filled with a phase shift material (24) and consist of an interior wall (2) that is designed to be installed on an interior side of the building, an exterior glazing (3) designed to be installed on an exterior side of the building, and an insulating wall (5) that consists of a granular silica aerogel/xerogel and is interposed between the interior wall and the external glazing. The phase shift material is opaque when it is present in a solid state, and is translucent when it is present in a liquid state. A melting temperature (Tf) of the phase shift material, with atmospheric pressure, is 21-27[deg] C. The interior wall and the external glazing are mounted in a frame (4). The insulating wall has a thickness of 20-40 mm, and is present in contact with the interior wall.; The element further comprises a curtain or a shutter mounted on the frame of the side of the exterior glazing. An air space extends between the interior wall and the insulating wall, and is delimited on one side by the interior wall and on other side by an intermediate glazing placed between the interior wall and the exterior glazing. An independent claim is included for a building envelope assembly.