A sliding window sash assembly glazed with vinyl film and adapted for easy attachment to framework openings in screened enclosures and the like for use as a wind break under adverse weather conditions is described. Both the window framework and the sash frameworks are fabricated of thin wall-section extruded aluminum members, and to prevent sticking and jamming of the sashes in the frame, improved slide members are removably fitted along the sash side rails and slidingly fitted in vertically-extending, T-shaped grooves formed along the insides of the window frame. The slides are fabricated of a resilient plastic material, hollow along their lengths for the reception of compression springs operative to frictionally press longitudinal side portions of the slide members against inner wall portions of the T-shaped grooves along which they slide.