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Secondary glazing and even triple glazing can make a significant impact on the way our home’s windows perform. But before you establish how to approach improving your windows, it’s important to understand the role that they play.
The homes that we live in now have more window area than they ever had. The more modern the home, it’s not just the number of windows, but the size of the glazing too. We want more glazed lanterns and rooflights to bring in light from above, bigger sliding doors to overlook patios and feature windows to allow sunlight to seep through our homes. That’s hugely positive in many respects but it also poses a significant challenge, too. Because our windows have no insulation compared to the walls they sit in, they can cause heat loss, leading to rising energy bills. So how do you improve your windows without compromising elsewhere?
When trying to get a fast quote for secondary glazing, it’s essential to remember that the solution will most likely be a custom made one. Therefore, to get a ballpark figure, you will need to know the number and size of your windows plus you may need to add any further additional requirements for your installation. Secondary glazing cost per window measuring 1-metre by 1-metre averages around £300/m2.
The average price for a white UPVC double glazed casement window measuring 1-metre by 1-metre is around £300/m2.
There are a number of different factors including the size of the windows you choose to have installed, the number of windows, the style of the windows, the material used for the frames, the company you choose to do the work, and whereabouts you live in the country. More and more of us live in flats than ever before, and the average cost to replace the windows in a flat with the newest double glazing is between £1,550 and £2,750.
Triple glazed windows typically cost between one fifth and one third more than double glazed windows. Installation of a standard uPVC double glazed window could cost around £300/m2, whereas a triple glazed one would be around £400/m2.
|Glazing cost||Range of costs|
|Lowest price||Highest price|
|Secondary glazing 1 window including labour||£300||£500|
|Secondary glazing 4 windows including labour||£800||£2000|
|Secondary glazing whole house (8 windows)||£1500||£4000|
|Replacement triple glazing area pricing||£400||£700|
*These are estimated average costs based on current market research and input from our expert tradespeople. Costs may vary.
The heat loss of windows and walls is measured by U-values. The lower the U-value, the better the energy efficiency. A typical modern double glazed unit achieves a U-value of around 1.6-2, while a single glazed window would have a U-value of around 5. For comparison, a triple glazed window would expect to have a U-value of around 0.7- 0.8 – doubling the performance of a double glazing window. For comparison, a well-insulated cavity wall would typically have a U-value of around 0.3 – with high-performing modern walls being built to around 0.15. That’s another way of saying that a single glazed window is around 10 times as cold as the wall it sits next to.
There are three main factors that influence how effective a window is at reducing heat loss. The glass itself, which is typically 4mm thick, can be upgraded to a low-e coating, which helps to keep heat in and cold air out. Secondly, the thickness of the cavity between the two panes of glass should be around 20mm. And lastly, that air gap can be ‘upgraded’ with the addition of gas such as argon. The key element, however, is the middle one – the air gap itself, and so anyone adding secondary glazing should look to maintain a 20mm gap between panes, while triple glazing tends to have optimum performance utilising two gaps of 16mm. Argon is used to fill the cavity because it insulates better and has less moisture content, reducing the risk of condensation. Also, to maximise the U-value, the thickness of the window panes themselves can be varied.
One of the most common problems with existing double glazed windows is condensation. If it’s present to the touch on the inside of the window, it is forming because the water vapour in the internal air is turning to water as it touches the cold window (this doesn’t happen with high performing double and triple glazed windows). There isn’t an easy fix for this problem apart from either trying to reduce the water vapour through extraction (it’s typically a problem in bathrooms and kitchens) or upgrading the windows. If there is condensation or misting in between the panes then it’s an indication that the seal between the two panes has degraded and needs replacing.
If you are one of the people who live in one of the 2-3m homes with single glazing, replacing the whole lot with double glazing can be very expensive. If your home is listed, it is likely to be also prohibited by your listed buildings officer or if your windows are particularly attractive, replacing them with double glazing is likely to have a negative impact on the home’s character. This leaves the addition of secondary glazing as the best option. Secondary glazing consists of an independent pane and frame positioned on the inside of the original window typically at a gap of around 100mm to the original. A new frame is installed into the window reveal and then the glass – which can slide open to allow ventilation. For most people the installation of secondary glazing is a job best left to a professional joiner or window company.
Windows have a long life expectancy. The air gap and thickness of the window panes is the same now as it ever was. The main weak spot is the rubber seals which isolate the air gap – they tend to degrade over time particularly if exposed to abrasive cleaning agents. If your seals are in good order the main reason to replace is usually that new double and triple glazing units tend to have superior energy performance than your original windows. Older plastic frames can discolour, too – so for most people window replacement makes most sense as part of a visual as well as energy-inspired overhaul.
Triple glazing is the next big thing in window glazing in the UK – having been a standard offer for windows on the continent for decades. The additional cavity and pane can typically cut the heat loss of a window in half and as a result comfort levels are hugely improved. The units and frames are thicker, meaning that you’ll get less of a window reveal, but for most people, the benefits are tangible, particularly on heavily glazed north and east elevations, which tend to be colder. The effects are a bit less noticeable on south and west-facing windows, where some experts believe triple glazing can detract from the benefits of solar gain in the colder months.
The replacement of doors and windows is covered by the building regulations. Window installers who are FENSA approved will be able to issue a FENSA certificate to show that your installation complies. It would be difficult to find window installation companies who do not offer a FENSA certificate. If you’re installing windows yourself or using a non-FENSA registered installer, you will have to independently apply for building regulations approval.
Most window suppliers have their own installers – either in-house or approved freelance installers. Using a non-approved installer means that your warranty may be reduced or even invalidated. Many of the triple glazed systems tend to have their own peculiarities for fitting so it’s always best to use someone well versed in the type of window you have chosen.