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What is causing a foggy, cloudy haze on windows and sliding glass doors?
Sunday, September 30, 2018
If you have window panes that are clouded over, it’s likely that they are double-pane (insulated) and have lost the inert gas sealed between the two panes of glass. Check to make sure that the hazy film is not on the outside by cleaning the glass first. The haze can be severe, like in the photo above, or less obvious unless there is glare on the surface, as in the photos below.
After about 20 years, the seals around the perimeter of the glass fail due to the fatigue caused by the expansion/contraction movement of repeated heat/cool weather cycles. When the pressurized gas escapes, humid outdoor air enters through the gaps and dew forms on the inside surface during temperature drops, which allows a growing layer of dust to adhere on the interior surface of the glass—and also, in some cases, the powder of moisture-absorbing silica pellets that were inserted at the factory to forestall moisture-intrusion problems.
While it is possible to replace only the sash (affected glass and frame around it), more often it is cost-effective to replace the entire window. Most real estate contracts that provide an allowance for repairs disclaim “cosmetic” defects, meaning ones that effect only the appearance of the home, like a stained carpet or scratched kitchen countertop, and some sellers will argue that a fogged window is only cosmetic. But the loss of the gas seal also destroys the insulating ability and rating of the window. Here’s an example of a sliding glass that lost its gas a long time ago, and this is definitely a material defect that should be repaired.
One repair alternative that is sometimes offered by window repair contractors is removal of one pane of glass instead of replacement of the window. This enables cleaning of the buildup on the inside surface of the outside glass pane and is less expensive than replacement of the entire window, but the insulating ability of the window is lost.
It is easy to tell, if you look carefully, at the difference between a single- and double-pane window. Holding a flashlight up to the glass surface at an angle will show two reflections in a double-pane window. Also, the spacer between the two panes will be missing when this type of repair is done. The left photo below shows a fixed-glass window with both panes intact and the spacer visible between panes. The right photo shows a nearby window that has had one of the panes removed, with the space gone and interior framing moved outward, leaving a gap at arrow.
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To learn more about doors and windows, see these other blog posts:
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