Similarly, if the window was installed too tightly into the frame without enough room for natural movement, any shift in the building’s foundation or extreme weather can force the frame to squeeze the glass until it breaks. Can You Repair a Cracked Inner Pane?
Double-glazed windows are hermetically sealed units filled with insulating gas, such as argon. These units are manufactured under specific atmospheric pressures. If there is a drastic change in pressure or altitude, the glass may bow inward or outward.
A double glazed unit cracked on the inside is not an emergency (unless in a child’s room), but it is a . The unit will eventually fog and lose insulation. Replacement of the sealed unit is the only permanent cure. Temporary taping can prevent shards from falling inward until repair is scheduled. double glazing cracked on inside
(US/UK, 2025):
I can then provide specific advice on the likely cause or help you find a repair specialist. Similarly, if the window was installed too tightly
If you discover a crack, check your warranty first. Many double-glazing installers offer 10-year guarantees that cover "spontaneous" glass breakage caused by thermal stress or manufacturing defects. If you'd like to resolve the issue quickly, tell me: Your (to find local glaziers) The age of the windows (to check for warranty coverage) The crack pattern (straight, wavy, or spiderweb)
| Cause | Mechanism | Typical Pattern | |-------|-----------|----------------| | | Solar heating of sealed unit creates temperature difference between panes. Inner glass gets much hotter than outer → differential expansion → crack. | Curved or wavy crack starting near edge, often at corner. | | Impact without outer break | Hard object hits inner pane (e.g., child’s toy, furniture moving). Outer pane remains intact because it was shielded. | Star-shaped or single point-origin crack. | | Edge stress / poor glazing | Unit installed too tightly in frame, no room for expansion; pressure transfers to inner glass. | Straight crack parallel to frame edge. | | Nickel sulfide inclusion (rare) | Tiny impurity in glass expands over time, causing spontaneous fracture. | "Butterfly" pattern – two cracks from a central point. | | Previous damage + temperature change | Small chip or scratch on inner pane (unnoticed) acts as stress riser; temperature cycling propagates crack. | Linear, growing slowly over weeks. | The unit will eventually fog and lose insulation
Maintain Airflow: Ensure there is at least a 2-inch gap between your curtains/blinds and the window glass to allow heat to escape.
: Partially closed blinds or objects placed on a windowsill can create sharp "shadow lines" where one half of the glass is hot and the other is cold, leading to stress along that line.
: Heavy black-out curtains or silver-backed blinds can trap a significant amount of heat between the fabric and the glass. This "heat trap" can rapidly raise the temperature of the inner pane.