Triple Glazed Windows

Should I go for triple glazing rather than double glazing?

In our view, generally, yes.

When using our systems the thermal performance of a triple glazed window is normally 40-50% better than a double glazed version but typically only 10-15% more expensive. Noise reduction can also be better depending on the glass used.

This improved thermal performance is delivered as a result of the extra insulation provided by the third pane of glass and the additional layer of argon gas. Couple this with a thermally efficient frame and you have a truly high performance window.

A number of our triple glazed windows are suitable for passive house development as standard.

BACKGROUND

Buildings have become more energy efficient over years as regulations have tightened and energy costs have soared. Environmental impact is also a factor. Around 22% percent of the UK’s greenhouse gas output comes from residential homes and domestic heating (source National Statistics). Reducing heating requirements by making homes as thermally efficient as possible will clearly reduce this level. 

Windows and doors play a key part in achieving this. In most houses 20-25% of heat is lost though windows and doors.

Thermally efficient windows and doors therefore have these benefits:

  • Make your home noticeably more comfortable
  • Reduce heating bills
  • Reduce carbon output and greenhouse gases

However this still means that 75% or more of your heat is lost through walls, floors and the roof. Making these areas more efficient though better insulation and draught proofing is obviously essential to creating a low energy home and capitalising on the benefits of using high performance triple glazed windows. Norrsken recommends a holistic approach to the thermal envelope of your building as part of specifying your windows and doors. 


COMFORT

With U-values in the region of 0.8 or better, triple glazed windows and doors from Norrsken will lose less than half of the heat of typical double glazed products. Triple glazed windows will therefore provide significantly better thermal performance than double glazed ones. 

As outlined above this benefit will only be fully realised when they are included as part of a thermally efficient whole building envelope. In other words, installing them in an unimproved, draughty and poorly insulated home will likely not be worthwhile.

On the other hand when they are included in a well designed, well insulated home with efficient heating and, ideally, heat recovery ventilation, the benefits they bring go well beyond what simple performance numbers can tell. On a cold day the glass on the inside of a triple glazed window is several degrees warmer than that on a double glazed version. 

Shown below are thermal models of a high performance double and triple glazed window when it is 0 degrees outside and 21 degrees inside. In both cases the coldest part of the glass is at the bottom of the pane. The inside pane temperature of the triple glazed model is 2.5 -3 degrees warmer over its whole surface than the double glazed version. This internal pane temperature affects the air in contact with it. This translates into a more comfortable feel on the inside, minimal convection of air internally and the sense of not being able to tell how cold it is outside; it is always warm comfortable and cosy inside.


typically around 25% of the heat loss from a home is through the windows and doors
Thermal image showing heat loss through windows. WIndows and doors account for 20-25% of heat loss in in a typical home.



"...many of our triple glazed windows have a U-value of less than 0.8 W/(m²K) – 50% better than the best double glazed windows."







elements of a high performance Norrsken triple glazed window
See also our "Performance" page
a double glazed window - showing the internal glass temperature when it is 0C outside and 21C inside
a double glazed window - showing the internal glass temperature when it is 0C outside and 21C inside


a triple glazed window - showing the internal glass temperature when it is 0C outside and 21C inside
a triple glazed window - showing the internal glass temperature when it is 0C outside and 21C inside


U-VALUES

U-values are a measure of heat loss through a material and are used to measure how effective elements of a building's fabric are as insulators; that is, how effective they are at preventing heat from transmitting from the inside to the outside of a building. 

U-values are measured in watts per square metre per kelvin (or Celsius) (W/(m²K)).The lower the U-value the better. 30 years ago in the UK walls in new homes were required to have a U-value of 0.6 W/(m²K) or better. Under current regulations they are required to have a U-value of 0.18 or below – a more than 300% improvement in insulation performance. 

U-values for windows and doors have similarly changed over time. A single glazed window has a U-value of around 5.0.  Early double glazed windows had a U-value of 2.5 - 3. Current building regulations state that windows in a new build house must have a U-value of 2.0 or better - although it must be said that this is not a particularly ambitious target.

Modern double glazed units use Low Emissivity Glass (Low-E) and argon or krypton gas in the cavity and the best double glazed windows can achieve a U-value in the region of 1.2 W/(m²K). By contrast, many of our triple glazed windows have a U-value of less than 0.8 W/(m²K) – 50% better than the best double glazed windows.




WHICH U-VALUE?

There are two commonly quoted U-value measurements for windows and doors.

Centre pane U-values. This is the measurement of energy conductivity through the middle of a pane of glass. Because it is measured away from the edges of the window – where more heat is lost – it will usually be a lower (better) number than the U-value for the window as a whole. It is often quoted as the Ug value

Window U-values. This is the measurement of energy conductivity through the whole window, including both the glass and the frame. It is known as the Uw value.

Norrsken normally provides both figures in our quotes, but the number we focus on when discussing window performance is the whole window U-value (Uw). This is the more complete value and more closely represents the actual real-world performance.

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