Fogging of Dual Pane Windows

A property inspection should always include checking the condition of windows. Often REALTORS® and property inspectors find dual pane (insulated) windows that are fogged. If the air seal between the panes of glass has failed, moisture intrudes into the sealed air space between the glass panes, thus causing the window to fog (forming water droplets) or become cloudy.

Detecting a defective window is often very difficult. The fogging can be slight or extreme, and can vary depending on weather conditions. Sometimes one can see the fogging effect only when looking through the window from the interior. It can be difficult to detect defective windows during the inspection because of factors such as lighting conditions, rain just before or during the inspection, or windows that are dirty, very high, or with a film tent. Most property inspection reports include a disclaimer regarding determination of the condition of insulated windows.

What can cause a window seal to fail? Harsh cleaning products or incorrect caulking. Extended periods of moisture, such as sprinklers spraying against the window, or wood frames without adequate weep holes in the frame. Improper installation as a new unit or as a replacement. Changing humidity levels and seasonal temperatures; sometimes windows did not appear to be

fogged during the inspection and then weeks or even months later, climatic changes caused the windows to fog. Tinting windows can cause a seal to fail, and will also nullify the manufacturer’s warranty; only factory-tinted windows are recommended.

One way to check for a failed window seal is to place an ice cube on the window for 10 seconds. After the allotted time, remove the ice and wipe the area clean. If condensation is left on the sealed side of the glass, this can indicate a bad seal and the glass unit will need to be replaced. It is difficult, if not impossible, to determine how long the seal has been bad. The amount of visible residue can be an indicator, but there is not standard method for relating residue amounts to time. Therefore, trying to judge when the window failed will be subjective and imprecise.

The standard window manufacturer warranty is five years; however, some manufacturers will warrant them for ten years or for life. It is quite common to find windows fogged around eight to ten years of age or more. Sometimes windows can become defective only a few years to improper installation.

The only way to fix a fogged dual pane window is to replace the glass component, which cannot be fixed in the field. Therefore, it is important to look at the windows again at the final walk-through (when weather conditions may be different) to avoid any disputes after close of escrow.