Window Seal Failure. How to Prevent it.

window seal failure

One day you peer out your window to see some strange fog on it.  You take your finger  and rub the condensation.  It doesn’t disappear.  Perplexed, you then check the outside of the window.  Again, you rub the condensation to finally realize that the condensation is between the window panes–better know as window seal failure.  Open up your wallet, since this is going to hurt.

What is Insulated Glass?

Insulated glass is known as double pane or thermopane.   The perimeter of two panes of glass are bonded with about a 1/2 to 3/4 space between them. According to Family Handyman, high quality double pane windows have two perimeter seals.  The inner seals resists water and corrosion, whereas, the outer seals provides strength and rigidity.

Some double pane windows have just a single seal.  Others have a hollow tube or spacer which keeps the panes spaced.  The tube generally has a moisture absorbing desiccant to keep the windows clear; however, once the desiccant is saturated, the moist air starts creeping in and the seal will fail.

How can you tell if your windows have failed?

Generally when the sun shines on a cool window, you can see the condensation.   I was able to see the condensation in both the summer (due to air conditioning) and winter (cold air outside) on my southerly windows.  However, you may not be able to tell if your windows on the northern side of you house have failed.  Watch the video below for an inexpensive way to find out if your windows have failed.

Why do Seals Fail?

In our nine year old New Jersey house, we  had 4  seal failures despite purchasing expensive low-e, argon filled double pane windows.  Cost, location,  and maintenance all play a part in seal failures.

Most seal failure occur in windows on the south or westerly side of the house. The sun causes expansion and contraction, which ultimately leads to failures.    All our seal failures were on the south and southeasterly side of the house.

Other factors that cause seal failures include:

  • Window seals which are exposed to water will break down quicker especially if they don’t have proper safeguards to prevent water puddling around the perimeter seal.  (See Figure B on Family Handyman’s article.)
  • Certain type of window frames have advantages and disadvantages:

“Window frames are available in a variety of materials. Frames can be composed of a single material or made of a combination of different materials such as wood clad vinyl or aluminum-clad wood. Each framing material has its advantages and disadvantages. Though ideal for strength and customized design, aluminum frames conduct heat and therefore lose heat faster and promote condensation as well. The corrosion and electro-galvanic deterioration of aluminum frames can be improved by placing continuous insulating plastic stripes between the interior and exterior of the frame or the frames can be anodized or coated. Wood frames have high R-values, are not affected by temperatures extremes, and do not generally promote condensation. Wood frames do require considerable maintenance in the form of periodic painting or staining. If not properly protected, wood frames can swell, which leads to rot, warping, and sticking.” [Source.]

  • Age.  Nothing lasts forever.

Since July, 2010, all ENERGY STAR windows  must be certified through a recognized program.  Sample  integrated glass unit are tested to withstand accelerated weathering over an extended period.  Accelerated weather includes extreme temperature swings, high humidity, and UV radiation.  Integrated certification requires manufacturers to implement in-house quality assurance.

“Field studies have shown that insulating glass failure rates differ greatly depending on the quality of seal systems and manufacturers’ quality assurance. Well-fabricated IG units can retain gas at a loss rate of less than 1 percent per year, resulting in only minimal loss of insulating performance.”  [Source]

How Can You Prevent Seal Failures?

Maintenance and shade from the sun are your first line of defense.

 “Separated sash frames (which allow moisture to reach the seals) and deteriorating perimeter seals can be caulked to increase the longevity of insulating glass. You can also help protect your double-pane windows by preventing excess moisture from accumulating on them; the best way to do this is to ensure good air circulation both inside and out.” [Source.]

As noted above, wood windows need to be checked every year to make sure the caulk around the panes have not cracked allowing water to seep into the wood.  In addition, the windows will have to be repainted periodically.  Water will cause wood rot and seal failure.

Most importantly, when buying new windows, be mindful of the length of the window warranty and what the warranty covers.  Our windows have a ten year warranty so my seal failures have been covered under the warranty.  Labor is not covered at this point.  Some window companies have longer warranties.  Read the fine print!

Family Handyman does a nice job summing how to prevent seal failures.

“But again, the single best safeguard against window failure in the future is to buy a top-notch window now. You get what you pay for.”

What happens if I have a seal failure?

Check  your warranty to see if you are covered; otherwise, you will have to have the window glass replaced.  If there is rot, you may have to have the entire window replaced as well.

Just an aside, it appears that there is a debate whether windows can be fixed through a process called defogging. I honestly, can’t speak to whether or not this practice works, but wanted to alert you to do your homework before choosing defogging as an option.

Join the Conversation:

  • What have you done to reduce the likelihood of seal failure?
  • Have many of your window seal’s failed?




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