Triple Glazing – is it worth the extra money?

Triple glazed windows are still a relatively new concept in the UK. But in colder countries like Scandinavia, where homes endure extreme winter weather, they have been a standard fitment for many years. While we might not get the same severity of weather conditions, the UK does still suffer from harsh winters and of course increasing energy prices. You must also remember there are other ways to insulate your home like the roof, walls and floor, but neglecting your windows can result in cold spots and condensation.

Benefits of Triple Glazing 

There are many benefits to installing triple glazing in your home but the important thing to remember is that all triple glazing is not the same. There are many systems available but to really get the maximum benefit, the gaps between the panes of glass should be 16mm and filled with argon gas. Argon is an inert gas that reduces the heat loss through the panes. If the gap is reduced then the thermal performance of the sealed unit is reduced, unless you start to use an expensive gas like krypton. So generally speaking the optimum size of a triple glazed sealed unit should be 4mm glass, 16mm gaps, so in our industry it’s called a 4/16/4/16/4 unit and that equals 44mm in total. If you just compare the u-values of the glass then the comparison between 44mm triple unit and a 28mm double glazed unit is large. The typical centre pane u-value of the 44mm unit is 0.62, the double glazed unit 1.1.

Typical U-values with triple glazed windows

You will see from the below that different sized units provide some very different u-values. These figures are based on the Veka Matrix system.

Sealed unit size        Unit make-up Glass u-value         Whole window u-value

  1. 28mm double            4/20/4                 1.1 1.4
  2. 36mm triple               4/12/4/12/4         0.76 1.1
  3. 40mm triple               4/14/4/14/4         0.68 1.0
  4. 44mm triple               4/16/4/16/4         0.62 0.8

Triple Glazing v Double glazing

Triple glazing very simply put is an extra pane of glass over a double glazed unit. However this enhances the performance in a number of ways:-

  • The extra pane of glass provides another barrier against the cold winter weather making your home warmer.
  • The extra pane also means an additional spacer bar at the edge of glass to reduce thermal transmittance
  • The extra pane provides additional security to the glass element of the window. The middle pane is normally toughened.
  • Sound insulation is marginally improved over a double glazed unit, if the same thickness of glass is used throughout.
  • Triple glazed windows can normally get the best Energy A++ rating
  • Low E glass
  • Low emissivity (low-e or low thermal emissivity). This is a coating applied to the glass that increases the thermal performance of the window. On a triple glazed window the internal pane and middle pane of the sealed unit should have a low-e coating. Low-e is a microscopically thin metallic coating applied to the glass that reflects heat back into the room.

U-Values in windows can become confusing because there are different ways of measuring it. Centre pane U-value measures the performance of the glass alone, whole window u-value includes the thermal performance of both the frame and glass. So the type of frame used also affects the performance, generally PVC offers greater thermal performance than say aluminium.

Solar Gain – G Value

The ‘G-Value’ measures the degree to which glazing blocks heat from sunlight. The G-value is the fraction of the heat from the sun that enters through a window. G-value is expressed as a number between 0 and 1. The lower a glazing’s G-value, the less solar heat it transmits. Triple glazing does not enhance the solar gain performance of the window, the better insulated a product the lower levels of solar gain.This is because triple glazing will normally have two panes of low-e glass. In the UK levels of solar gain are lower because of our climate and it would mainly only apply to South facing elevations. To put this in simple terms, the greenhouse effect. A single glazed greenhouse is great for solar gain, a triple glazed one not so good. If you wanted to keep the greenhouse warm at night then triple glazing would be much better than single glazing, so its a balance.

You also need to factor in the number of chambers within the frame, the fewer chambers the less insulated the frame. The Veka system uses thermal inserts within the frame to improve the insulation further, whilst the Residence 9 windows have a market leading nine chambers in a frame of 100mm depth.

Are there any triple glazing downfalls?

Are there any down-falls I hear you ask? The biggest problem I’ve encountered with my own windows would be the external condensation on the glass. This happens because the external pane of glass is not being heated so well by your house, so if the glass drops to less in temperature than the outside air, then you reach “dew point” and condensation forms. It’s the exact reason that you get dew on your car windows. It will generally happen after a cold clear night and it would best be described as a light misting that forms from the centre of the pane, actually it’s the complete opposite place it would form on the inside. This is because the glass in effect is being heated through the frame and spacer bar, so the outer edge of the glass is warmer than the centre. When you get internal condensation it’s the opposite way, because in reverse the outer perimeter of the internal glass is the coldest.

You can find that ‘A’ rated double glazing will suffer from the same problem, but the effects are much less They usually clear fairly quickly in the morning, so it certainly does not bother me.

Light Levels and Triple glazing

Light? Having three panes of glass, with two of them having a low e coating, there would be a drop in the natural light coming through the window as the low e coatings darken the glass slightly.

Triple Glazing Security

Security? Three panes would have to be more secure than two, so there is an obvious difference. The middle pane of a triple glazed unit should be toughened, especially if the glass faces a sunny elevation. This helps with the stresses that occur with the heat build up within the sealed unit, especially important on a hot and sunny summers day. Yes they do happen in the UK sometimes! 

Is Triple Glazing worth it? – Triple Glazing Cost

Triple glazed sealed units are more expensive than double glazed ones obviously.It works out as a simple extra square metre cost usually that we are happy as a company to show as an extra cost. In the UK houses lose up to 20% of heat through the windows alone, so some would say if you are changing your windows, then fitting the best insulated products is the most sensible thing to do. You then need to factor in the extra cost of triple glazing against the saving in heating bills, the payback time will certainly not be over-night, that said a customer once said to me “we would like to live as comfortably as possible, so we feel triple glazing is the right product for us”  The decision ultimately will be your own!

Triple Glazing is it a ‘green’ product? What about the carbon footprint?

Is triple glazing a green product? This will always be the most difficult question to answer. The energy and material required to manufacture glass and the sealed unit, including the extra spacer bar will add to the carbon footprint of the product.

Triple glazing sound insulation

The next thing you might find on the internet about triple glazing is improved sound insulation. There is a lot of misinformation out there and many claim it improves sound insulation because they believe three panes are better than two. Scientific tests would show that if all three panes are the same thickness of glass then the benefit to sound insulation is very marginally better at best.

If you introduce one different thickness of pane, say one pane of 6mm glass and two panes of 4mm then this would improve the sound insulation more, because the different thicknesses of glass will change the wavelength of the sound as it passes through the glass, thus reducing the sound transmittance. It would be worth pointing out at this stage that an open window will stop nothing and then there is my other pet-hate “trickle vents” that are notorious for leaking sound. That is a subject for another blog as there are better quality trickle vents on the market. 

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