Screening arrangement in a ventilation system

An arrangement for screening off a ventilated space (5) in a floor construction in a building, which space (5) forms part of a ventilation system, which floor construction is arranged on a subfloor (2) and comprises a plurality of joists (6) arranged at a pre-determined distance from each other and supported by a plurality of level-adjusting spacer screws (8) resting on the subfloor (2) to create a free passage (9) between the joist (6) and the subfloor (2) as well as said space (5), which includes said passages (9), between the subfloor (2) and the floor construction, characterized in that it comprises an elongate plate-shaped body (116) that is impermeable to air and includes a flat waist part (117), a foot part (118) and a top part (119), which foot and top parts (118, 119) extend along the long sides of the waist part (117) and are flexibly connected to the waist part (117) by means of joints (122, 123) that are parallel to each other, which plate body (116) is arranged to be anchored with its top part (119) to a vertical side of one of said joists (6) by means of attachment elements (120) and arranged to be anchored with its foot part (118) to the subfloor (2) by means of attachment elements (121), the waist part (117) being arranged to form a right or acute angle with the subfloor (2) so as to form an airtight screen between two sections of the ventilated space (5) or between the ventilated space (5) and a non-ventilated space in the floor construction.