A system for creating a dead air space between an existing window and window frame, and a piece of glazing is described. The system includes a sealing strip for spacing the piece of glazing away from the existing window and to seal the space there between when a sealing strip is properly compressed. The strip is compressed by employing a plurality of compression clips, each clip having an anchor part for mounting the clip on the window frame, a contact part spaced away from and movable with respect to said anchor part for compressing the piece of glazing against the sealing strip, and an adjustment part for adjusting the space between the anchor part and the contact part. The compression part further includes a compression gasket mounted between the piece of glazing and the compression clips.