Is Triple-Glazing The Answer For The UK Market?
Window technology has now progressed significantly. In that good quality triple glazing can admit more energy to a building than will escape over the annual cycle. So long as the solar access is fair. This remarkable fact enables Passivhaus designers to create buildings with very low heating demands, whilst providing high levels of comfort to the occupiers.
For a long time now triple glazing has been seen as an expensive specialist product. Energy efficiency requirements within the window industry have become increasingly challenging. However, triple glazing is now establishing itself within the mainstream glazing market.
With pressure to save energy and to reduce homeowners energy bills. Properties in the UK are becoming more and more energy efficient. Energy performance certificates are compulsory when selling your property. Your windows play an important part in the overall rating given. In the Replacement window or double glazing industry, which many people still know it as. Home owners are now being encouraged to switch from double to triple glazing. You may not have noticed this yet, but the pressure is on to improve the energy performance of windows and mere double glazing will soon no longer be enough.
The U-Value measurement
The method of comparing the energy performance of windows is to use the U value measurement. Just as we do with walls, floors and roofs. Traditional windows, with a single pane of glass in them, have a U value in excess of 5. Double glazing in years past used to score over 3. Over the years, the manufacturing process has undergone a number of improvements. Currently the Building Regulations (FENSA & Certass) insist that any window you install should have a U value no worse than 1.6.
These improvements have been brought about by the introduction of wider cavities between the two panes of glass. Our double glazed sealed units are 28mm sealed units, (4mm glass 20mm gap 4mm glass). This is pretty much the optimum distance for double glazing. Low-emissivity coatings have been being added to the glass to stop heat escaping. The cavity has being filled with an inert gas, usually argon. Cold bridges, such as aluminium spacers, surrounding the glazing have been designed out of new windows. A U value of 1.6 may look good when compared to U-Values of 10-15years ago. But compared to the U value demanded for walls – currently less than 0.3 and due to fall even lower. You can see that windows remain weak spots in the overall thermal efficiency of the building envelope. Hence the tremendous pressure to improve their performance even further.
Our Current U-Values
Kommerling Upvc Windows
With our standard range of Kommerling Upvc frames (O70 Gold). We achieve a U-Value on our double glazing Upvc Windows of 1.3. When introducing triple Glazing we achieve a U-Value of 1.1.
Residence 9 Window System
With our Residence 9 Flush Casement Window. We achieve a U-Value on our double glazing of 1.2. When introducing triple Glazing we achieve a U-Value of 0.8. This meets the passiv-haus standard of requirement.
Glenfield Hardwood Flush Casement
Our 44mm triple glazed Glenfield window is 0.89 u value.
We don’t do triple glazing in any other wooden window range currently.
Should we switch to triple glazing?
The additional energy saving difference between double glazing and triple is quite small really. The payback time for double and triple glazed windows is high compared to other energy efficiency improvements. However it will help reduce any noise levels from outside even further and help to retain heat.
The main benefits for going for Triple Glazing are to do with levels of comfort. If you insulate all other areas of your property, floor, walls, roof, which people typically do. But you ignore the glazing, you will end up with cold spots around the windows. This can lead to draughts and streams of condensation running down the panes of glass. So, to summarise the quality and standard of glazing has to match the standard of insulation everywhere else in the property. So that the warm wrapping around your property performs consistently.
A-Rated double glazed sealed units should be a must. In fact most window companies are now offering this. But since the cost has come down. Why not go for triple glazing and achieve the maximum thermal efficiency for just a small additional expense ?
How to Solve Condensation
Which is where triple glazing comes in. Because if double glazing makes a modern house more comfortable to live in, triple glazing makes it even more so.
The physics involved here have been worked out in Germany by the Passiv-Haus Institute. It has shown what happens to surface temperatures on various forms of glazing. When it gets really cold outside and the internal air temperature is designed to be at 21°C:
- Next to a single glazed window, the internal surface temperature is around 1°C.
- Next to a double glazed window (2000 vintage), the surface temperature is around 11°C.
- Next to a modern, energy-efficient double glazed window, the surface temperature is 16°C.
- Next to a triple glazed window, with a centre-pane U value of just 0.65, the temperature is 18°C.
So you can see that whilst a double glazed window is perfectly adequate. A triple glazed one is just that much more comfortable. It hangs onto heat just that little bit better. So whilst triple glazing may make little difference to your heating bills. You will notice the difference inside the house.
The PassivHaus standard promotes the use of triple glazing for precisely this reason. – i.e. comfort – although it also states that the frames themselves have to be insulated, and the windows need to be mounted in the correct location within the wall assembly.
Windows behave rather differently to walls and roofs. When the sun is shining, they are capable of absorbing heat. In fact, the very best double glazed windows are already capable of being net heat contributors over the course of a heating season. In contrast, triple glazed windows slightly reduce the heat absorption characteristics of a window.
To reflect these complexities, the British Fenestration Rating Council has devised a scheme for the energy labelling of windows, from A down to G. The top rating is reserved for windows that are reckoned to absorb as much heat as they lose. They include both double and triple glazed windows.
Code for Sustainable Homes
There are many who argue that triple glazing simply doesn’t make sense in a climate like ours. Triple glazing is more costly to produce and produces much heavier sections. It has an embodied energy approximately 50% higher than double glazing.
So why are we even thinking of going triple glazed? It’s all to do with the Code for Sustainable Homes. The Government is using as a roadmap for us to move towards building zero-carbon homes by 2016. The Code more or less requires us to adopt the ultra-low-energy Passiv-Haus standard. This demands windows with a U value no higher than 0.8 — triple glazing with insulated frames. The UK market is still quite a way from this, but it is slowly getting there.