Most modern windows are equipped with double or triple glazing in the form of insulated glazing units (IGUs). These IGUs have an airtight seal at the perimeter that traps some type of gas between the window panes—usually argon, but sometimes krypton or ordinary air.
Ideally, the IGU perimeter seal is permanent. If the IGUs are filled with argon or krypton—gases that improve the IGU’s energy performance—you don’t want any of the precious gas to leak out. Moreover, you never want any humid air to enter into the space between the glass panes, since the entry of humid air can lead to condensation between the panes (sometimes called fogging).
IGUs perform well when they are installed at an altitude close to that of the factory where the IGUs were assembled. However, if IGUs from a sea-level factory are transported to a job site at a high elevation—usually defined as a location above 5,000 or 6,000 feet—then all kinds of bad things can happen:
- Since the atmospheric pressure above 5,000 feet is much lower than it is at sea level, the panes of an IGU can pillow out—that is, become convex—distorting the view through the windows.
- The IGU’s perimeter seals can be stressed, leading to leaks that allow argon to escape or moist air to enter the space between the panes.
- If the argon escapes, the window’s U-factor may not match the U-factor promised by the window manufacturer at the time of sale.
- In some cases, the glass can shatter.
These are old problems
Window experts have been aware of the problems associated with high-altitude installations of IGUs for decades, and many technical articles address the problems. Back in 2000, for example, BuildingGreen published an article on the topic called “High Elevation Problems Jeopardize…