You touch the pane. It’s smooth. The crack is on the inside—but between the two sheets of glass.
Consider it a gentle, visible reminder: every high-tech system, no matter how well sealed, has a lifespan. When the line appears, it’s time to give your window a second life—one clean, warm, crack-free unit at a time. If the crack is on the room-facing side (i.e., you can feel it) and the window is still fog-free, that is likely impact damage. You can temporarily cover with clear packing tape to prevent shards from falling. But if it’s between the panes, as described above, see Part 5—repair is not an option.
Your window frame expands and contracts at a different rate than the glass. If the installer used too little glazing tape or overtightened the retaining beads, the frame pinches the IGU. Over a few seasons of expansion, the inner pane, which has less flexibility than the outer (being further from the external buffer), gives way.
