Building facade system , comprising: a frame structure ; an outer pane supported by the frame structure and forming an interface with the outside air (B); and an inner pane supported by the frame structure , spaced from the outer pane by a distance (A), and arranged to face the building (C); the frame structure defining, with the outer pane and the inner pane , an inter-pane space ; the frame structure comprising: a first opening allowing gas flow between the outside air and the inter-pane space, and a first closure mechanism adapted for closing the first opening in a substantially airtight manner, the building facade system being characterized in that the frame structure further comprises: a first moisture-responsive control element that communicates with air in the inter-pane space and that opens or closes the first closure mechanism via a moisture-responsive dimensional change of the control element that depends on the relative humidity in the inter-pane space ; and a second opening that allows gas flow between the outside air and the inter-pane space, the second opening also being opened or closed by the first closure mechanism and the first moisture-responsive control element . a frame structure ; an outer pane supported by the frame structure and forming an interface with the outside air (B); and an inner pane supported by the frame structure , spaced from the outer pane by a distance (A), and arranged to face the building (C); the frame structure defining, with the outer pane and the inner pane , an inter-pane space ; the frame structure comprising: a first opening allowing gas flow between the outside air and the inter-pane space, and a first closure mechanism adapted for closing the first opening in a substantially airtight manner, the building facade system being characterized in that the frame structure further comprises: a first moisture-responsive control element that communicates with air in the inter-pane space and that opens or closes the first closure mechanism via a moisture-responsive dimensional change of the control element that depends on the relative humidity in the inter-pane space ; and a second opening that allows gas flow between the outside air and the inter-pane space, the second opening also being opened or closed by the first closure mechanism and the first moisture-responsive control element . a first opening allowing gas flow between the outside air and the inter-pane space, and a first closure mechanism adapted for closing the first opening in a substantially airtight manner, the building facade system being characterized in that the frame structure further comprises: a first moisture-responsive control element that communicates with air in the inter-pane space and that opens or closes the first closure mechanism via a moisture-responsive dimensional change of the control element that depends on the relative humidity in the inter-pane space ; and a second opening that allows gas flow between the outside air and the inter-pane space, the second opening also being opened or closed by the first closure mechanism and the first moisture-responsive control element . a first moisture-responsive control element that communicates with air in the inter-pane space and that opens or closes the first closure mechanism via a moisture-responsive dimensional change of the control element that depends on the relative humidity in the inter-pane space ; and a second opening that allows gas flow between the outside air and the inter-pane space, the second opening also being opened or closed by the first closure mechanism and the first moisture-responsive control element . <EOS>