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How Long Do Double Glazed Windows Last?

Graeme Clarke October 02, 2018 Double Glazing

Double glazing your timber windows is one of the most effective steps you can take to insulate your home and enjoy all the benefits that come with high-performance windows.


But, how long do double glazed windows last?

How long before you’ll have to invest more money into your windows in order to achieve the energy efficiency, air quality, security, and acoustic enhancement that double glazing offers?

Here’s a look at the life expectancy for double glazed windows and what factors determine how long your wood windows will last once you have them double glazed.



Is There a Warranty for Double Glazed Windows?


In the industry there is a standard double glazing warranty of 10 years.

That may seem like a long way off right now, but you’re not going to be happy if your wooden windows are starting to rot and your double glazing starts deteriorating in a few years due to some common poor installation techniques.

Even worse, imagine buying a home with double glazed timber windows, assuming you won't have to put any money into the windows, only to find out there are only two or three years left on the warranty.


Whether the insulated glass unit, or IGU, ends up failing within the warranty period, or you have to reinvest because the double glazing wasn’t installed well and the polysulphide seal around your unit is deteriorating beyond the warranty, you’re not getting the longevity you should be getting out of your double glazed windows.

But, the reality is, the standard industry procedure for double glazing wooden windows is only expected to last for about ten years. The way a lot of IGUs are put in, they are basically doomed to fail well before you are ready to deal with spending more money on your windows.

In fact, if double glazing is installed so it can live up to its potential, you won’t have to worry about them for decades.



Why Is the Double Glazed Window Life Expectancy So Short?


Water and improper installation methods.

No matter what you or your window company does, water is going to get inside your windows.


Especially with timber windows, any amount of moisture is too much. Water won’t just rot the wood. It will also cause the double glazing itself to fail.

What often happens is, window installers will put the IGU into a square rebate. Then, they seal the window, usually with a commonly used silicone sealants.

At first, the IGU is tightly sealed and your timber joinery looks safe from damage. But unfortunately, this isn’t the case. Over time, the problems that are intrinsic to this design will begin to manifest, damaging the double glazing until it fails.

  • Because the IGU is sitting in a square rebate, it is vulnerable to the water that gets stuck in the aaarebate.
  • Water vapour will eventually saturate the seal. The moisture can pull contaminants out of the aaasilicone sealant which basically results in water that is concentrated with dirt and contaminants. aaaThis can slowly deteriorate the polysulphide seal of the IGU.

Once the seal becomes damaged, the double glazing has failed. Moisture and air can get into the double glazing unit. This is where you’ll get that misty look on the inside of the glass.


The worst part is, there’s no repairing the window at this point. The only way to fix it is to replace the double glazing.

How long should double glazing last before misting?

It depends on the amount of moisture your windows are exposed to. You’re not going to see problems overnight, but without a different double glazing solution, the issues are inevitable. It may take several years. It may fail after the 10-year warranty, in which case you’ll need to replace the double glazing and you won’t have warranty protection.

Keep in mind, it’s not rainy weather you’re worried about. It’s the water vapour in the air that is going to slowly but gradually ruin your wooden windows.

You can’t stop the water from getting in, no matter how well the windows are sealed. What you can do to increase the longevity of your double glazing and ensure it lasts longer – decades longer – is make sure any water that gets in, has a way to get out.



How Long Do Wood Windows Last When Double Glazed for Longevity?


At Thermawood, our entire process is designed around longevity.

We retrofit double glaze timber windows so you can keep your existing wooden windows – and the charm and quality of real timber – but also experience all the benefits of new double glazed windows:

  • Lower energy costs and less wasted energy;
  • A quieter, more comfortable home; and
  • Better air quality and a safer home.

But, we don’t stick your IGU into a square rebate and seal it all the way around – trapping it with the very thing that will destroy it.

We developed a patented dry Retrofit Double Glazing system that lets any moisture that gets in your windows out.


  • Instead of a square rebate, we use special tooling to create a 15-degree slope underneath the aaaIGU.
  • With our special draining system, every 100 millimetres there is a drainage slot, which causes aaamoisture to drain out underneath the timber bead.
  • Instead of exposing your IGU to Silicone or another similar sealing technique that reacts with aaamoisture by eating away at the double glazing causing the IGU to mist and fail, we use solid aaasilicone blocks to support the double glazing to form what is known as a dry glazing system.

This means nothing comes into contact with the IGU. There are no seals or silicones or pooled moisture that can touch the insulated glass unit and potentially damage the polysulphide seal – which has to stay intact to preserve the double glazing.



And Now How Long do Double Glazed Windows Last?


At Thermawood our retrofit double glazed timber windows last for decades. The way we see it, they should last – at least – for 25 years, not 10. And, there’s no reason they won’t last a lot longer because nothing is going to damage the double glazing.

That’s what we’re about. A sustainable, efficient solution that will last a lifetime, not a moment in time.




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