Should you replace your old uPVC windows?

This is a question we often get asked by homeowners who already have uPVC windows in their property so, if replacing yours is something that you have been thinking about, here are the answers to common questions that may help you decide.
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How are uPVC windows made?

The first thing to understand when answering the question of possible replacement is that your double glazing is made up of three elements.

The Frame

This consists of two parts, the frame that fits into the window opening and the frame that holds the glass. They are both made from uPVC which has many benefits over old timber frames that it replaced. They are much lower maintenance and, if fitted correctly will not warp, crack or flake over time. That’s not to say they will last for ever but are likely to outlive the life of the other elements.

The Sealed Glass Unit

This is at the heart of the uPVC window and consists of two (or sometimes three) panes of glass with a gap between them that is either a vacuum or is filled with dehydrated gas to reduce heat transfer and create an hermetically sealed unit. A spacer bar holds the glass at a fixed distance apart and the sealant is applied to hold the glass together and stop vapour entering the unit. Desiccant or drying agent, is incorporated into the spacer bar to absorb any moisture that permeates the unit.

uPVC window company Swindon handle choicesThe Window Mechanisms

These are the hinges, handles and locks that ate attached both to the external frame and the window frame itself. These too will have a life expectancy which is often not as long as the frames themselves

How old are my uPVC windows?

Unless you have had the uPVC windows fitted or the previous owner advised you if they did, it is impossible to tell how old they are. However the majority of homes built after the early 1980s will have been fitted with uPVC windows to meet thermal regulations and many of those built earlier will have had the old ones replaced. To give you some idea of the scale of the double glazing industry, there are over 12,000 window installers in Britain fitting between 25 and 250 frames a week. That’s an awful lot of windows.

Also be aware that any upVC windows manufactured before 2007 will only have been ‘C’ rated at best, in terms of their energy efficiency. New uPVC windows being installed today should be at least A rated. Indeed, our A Rated glass has been is measured to be at least 25% more efficient than most currently installed double glazing. That will translate to a decent annual saving on your heating bills!

How long do uPVC windows last?

A commonly held view is that the sealed glass unit should last for around 20 years although poorly installed windows can fail much earlier. The main reason for failing is that the sealant around the edge which, by its very nature will allow some moisture to enter from the outside, gradually loses its performance. This is generally dealt with by the desiccant, but over time this will get saturated and will be unable to cope with the increased amounts. When the seal is in contact with this moisture for any length of time, it will fail.

You ought to also be aware that it is not just the double glazed units that can fail. The window mechanisms and other elements can do so too and this can be a problem with older windows as replacements may be hard to find.

uPVC window company Swindon noise reductionDo my uPVC windows need replacing?

There are some clear indicators that a uPVC window is coming to the end of its life.

Misting inside the units

This is the most obvious sign that your uPVC window needs replacing. What has happened is that the seal has failed and the gas that used to minimise heat loss has leaked out and has been replaced with moist air. Your window will be inefficient at retaining heat or minimising heat loss.

Condensation on the inside of the windows

Again this indicates that cold air is making its way to the inside pane and the efficiency of the window has been compromised.


These generally indicate that either the seal around the window frame has deteriorated or that the drain holes are blocked. Depending on the severity, these faults can be rectified but it may be time to consider the overall performance of your double glazing at this point.


These have much the same causes as leaks and the same remedies. This situation isn’t terminal but perhaps now is time the time to consider replacement rather than spending money on windows that are beginning to cause problems

Do uPVC windows lose their insulating properties?

As we have shown above your uPVC windows can develop faults that will reduce their thermal performance. However there is another point to consider here. The effectiveness of the window is directly affected by how big the gap is between the panes which is governed by the spacer bar. Older windows used to have a gap of around 6mm whereas modern units tend to be around 16mm. It follows therefore that if you replace your older uPVC double glazing with modern ones your home will be much better insulated and your fuel bills will decrease.
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Do you get bothered by noise?

One of the great benefits of double glazing is that it reduces the amount of noise transmitted into the home.

Without doubt the world has become a noisier place what with road traffic, air traffic, industrial activities and sadly increasing anti-social behaviour… we seem surrounded by noise these days even in previously tranquil locations. One answer is to fit modern double glazed windows with the wider space between the panes or even better go for an acoustic glass option or triple glazed units.

Will replacing my uPVC windows add value to my home?

There is no doubt that old and yellowed double glazed windows will adversely affect the value of your home and replacing them with modern new ones that are more thermally efficient will make a big difference. Consider too that modern double glazing comes in a much wider range of profiles and colours other than white. There are styles to harmonise with the age and architecture of your home which greatly improves the overall appearance of the property.

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We hope that this information has been useful and as the above shows there are many reasons why now may be the time to consider replacing your old double glazed uPVC windows. If you would like any advice about your existing uPVC windows or more information about the many new window options available to you please contact us. We would be delighted to help you.

Here at KM Windows and Doors we have an outstanding range of modern uPVC windows to meet every requirement. Take a look at our uPVC window range to find the perfect windows for your home – and don’t forget we offer a free no obligation quotation service too. For full details click here. We look forward to hearing from you.

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