Sealed Unit Failure
The breakdown of the hermetic seal in an insulated glass unit, allowing moisture to enter the cavity and causing persistent fogging or condensation between the panes.
Sealed unit failure (also called "blown seal" or "foggy window") is one of the most common window problems in Canada. It occurs when the primary and secondary seals of an IGU degrade, allowing moist air to infiltrate the gas-filled cavity. The moisture condenses on the interior glass surfaces, creating a permanent fog that cannot be wiped away.
Most IGU manufacturers warrant their sealed units for 10-20 years. Failed units must be replaced — repair attempts (drilling and injecting) are generally ineffective long-term. In many cases, the glass can be replaced without removing the entire window frame.