Sliding Window Rough Opening Size: Why the Wall Opening Decides the Fit
The Wall Opening Is the Spec A sliding window starts with the opening in the wall, not the number printed in the catalog. That distinction sounds minor until a frame arrives on site and refuses to sit flat because the rough opening is 6 mm tight at one jamb, 10 mm out of plumb at the head, and slightly bowed at the sill. On a slider, those errors do not hide behind the hardware. The track and sash make them obvious. ...