Permanent formwork for the production of vertical walls for separating an inner space from an outer space, this permanent formwork comprising: - a front panel of which an essentially planar front face is oriented towards the inner space; - a flexible rear panel of which a face is directed towards the outer space and delimits the outer periphery of the formwork; - at least two connection elements distributed along the periphery of the formwork, each connecting the front panel to the rear panel so as to form between the said panels a space able to be filled with liquid concrete, these connection elements being parallel and separated by a distance d when the permanent formwork extends rectilinearly along a horizontal direction, each of these connection elements comprising: • at least one hook for fastening the rear panel; • at least one spacer extending between front and rear ends bearing respectively against the front panel and the rear panel; - a set of main through-slots formed in the rear panel, the spacing between two main slots, which are consecutive in the horizontal direction, being equal to the distance d to within ±5%, each slot being able to be traversed by the fastening hook of the respective connection element; characterized in that: - additional through-slots are formed in the rear panel, on either side of each of the main slots, in the horizontal direction, the spacing e between each main slot and the additional slots formed on either side of this main slot being between 7 and 35 mm, and - the rear end of each spacer is movable by hand from a rest position in which the front and rear ends of the spacer are aligned on an axis perpendicular to the front face of the front panel, towards an offset position in which the rear end is moved away, in the horizontal direction, from its rest position by a distance equal to e/2. - a front panel of which an essentially planar front face is oriented towards the inner space; - a flexible rear panel of which a face is directed towards the outer space and delimits the outer periphery of the formwork; - at least two connection elements distributed along the periphery of the formwork, each connecting the front panel to the rear panel so as to form between the said panels a space able to be filled with liquid concrete, these connection elements being parallel and separated by a distance d when the permanent formwork extends rectilinearly along a horizontal direction, each of these connection elements comprising: • at least one hook for fastening the rear panel; • at least one spacer extending between front and rear ends bearing respectively against the front panel and the rear panel; • at least one hook for fastening the rear panel; • at least one spacer extending between front and rear ends bearing respectively against the front panel and the rear panel; - a set of main through-slots formed in the rear panel, the spacing between two main slots, which are consecutive in the horizontal direction, being equal to the distance d to within ±5%, each slot being able to be traversed by the fastening hook of the respective connection element; - additional through-slots are formed in the rear panel, on either side of each of the main slots, in the horizontal direction, the spacing e between each main slot and the additional slots formed on either side of this main slot being between 7 and 35 mm, and - the rear end of each spacer is movable by hand from a rest position in which the front and rear ends of the spacer are aligned on an axis perpendicular to the front face of the front panel, towards an offset position in which the rear end is moved away, in the horizontal direction, from its rest position by a distance equal to e/2.