Double Glazed Window Cracked Inside Patched -

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.

On a sunny day, the gas between the panes heats up, expands, and presses outward on both glass sheets. At night, it cools, contracts, and pulls inward. This daily breathing is normal. But if the perimeter seal is old or poorly fitted, the pressure becomes uneven. Eventually, the inner glass—the side facing your conditioned home—shatters from fatigue. double glazed window cracked inside

This is the window industry’s hidden demon. Tiny, microscopic specks of nickel sulfide can be trapped in the float glass during manufacturing. Over years, these impurities slowly change crystalline structure, expanding by up to 4%. In a standard single pane, this causes a harmless chip. In a sealed, stressed IGU, it acts like a bullet from the inside. The crack often appears as a distinctive “figure eight” or butterfly shape, originating from a single point. Your window frame expands and contracts at a