Abstract: Device for mounting plastic sheets on roofs or walls of greenhouses or other heated buildings with large window areas. A mounting flange is pasted or screwed to the pane or sash. The mounting flange includes a projection having a head with an inclined face facing the base of the mounting flange. A clamping member including a wedge-shaped base having an aperture therein is placed over the projection. As the clamping member is moved parallel to the mounting flange, shoulders on the clamping member adjacent the aperture engage the inclined face of the projection head to press the plastic sheet firmly between the clamping member and the mounting flange. Resilient tongues are provided on the clamping member to prevent accidental removal of the clamping member. Provision is made for placing a wire through a plurality of these devices to further hold the plastic sheet in position.