The haze that obscures the glass in double-pane windows is caused by loss of the insulating gas sealed between the panes. This allows air to seep in, and then the humidity in the air to condense on the interior surface of the panes. Dust particles in the incoming air adhere to the wet glass and build up in layers over several years  time. All double-pane windows lose their insulating gas evenutally, but there are two things you can do to keep the seal intact longer:

•• Do not pressure wash the windows. Pressure washing flexes the outside pane, with corresponding movement at the seal. It is possible to break the seal sufficiently to lose all the inert gas quickly when blasting a window with high-pressure water. We sometimes inspect a home less than 10-years old that the homeowner has pressure-washed and 90% of the windows are clouded over. 

•• Provide shade at windows with direct afternoon sun exposure. “Thermal pumping" is the repetitive flexing in and out of the glass, due to expansion and contraction, of the glass and surrounding frame and seals that is caused by big, abrupt changes in temperature. Sides of a home exposed to direct sun are more prone to the effects of thermal pumping, and windows with southern exposure are the most likely to have this problem. Shading those areas with an awning or foliage, for example, will reduce thermal pumping. 

    And premature failure of the window seals can be caused by a manufacuturing defect. This is the most likely scenario if most of the windows fail within a few years. Vinyl windows have a higher rate of expansion/contraction that other window frame materials, resulting in more stress on the seals, and may have a higher early failure rate. The vinyl window shown at the top of this page has a southern exposure, no shade, and had lost its gas and began to haze over at three years old.

    Also, double-pane sliding glass doors can have this problem too.

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

• Does a home inspector check insulated windows for brokens seals and lost gas?

• What causes sweating (condensation) on the inside of windows in the winter? 

• 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 is 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? 

• What are the code requirements for safety tempered glass for doors?• 

• Should a front door swing in or out? 

• 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? 

• 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?

• How can I tell if a window or sliding glass door is double or triple pane (insulated) glass?

• 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.