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 photo 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.

    Also, see our blog posts What causes sweating (condensation) on the inside of windows in the winter? and Where is safety/tempered glass required for the windows of a house?

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  To learn more about doors and windows, see these other blog posts: 

Is every exterior door of a house required to have a landing outside? 

 What are the small slots at the bottom of the outside of my window? 

Why does condensation form on the outside of some windows and not others in the morning? 

Why if the garage door track a white tube? 

What is the raised metal plate on the floor under the garage door?

 Why do I have to hold down the button to close the garage door? 

How can I tell if a window or glass door is safety glass? 

Should a front door swing in or out? 

Why is pressure washing double pane windows an expensive mistake? 

How many exit doors are required for a house?

 How many exit doors are required for a mobile/manufactured home? 

Are openable windows required to have window screens? Will windows with no screens pass a home inspection? 

Can a bedroom door open into the garage?

What are the building code requirements for a door from the garage to the house?

What is "low-E" window glass? 

What does ANSI 297.1 on glass mean?

Why is a double cylinder deadbolt lock on an exterior door a safety hazard?

How can I check my garage door to make sure it is safe?  

What is an egress window?

What does a home inspector check on an electric garage door? 

• What is the tempered label on glass at windows and sliding glass doors called?

• Do I need to have two exterior exit doors in my house? 

• When is safety glass required for windows at stairs and stair landings?

    Visit our DOORS AND WINDOWS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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