triple glazed bay windows

Can You Replace a Window Without Replacing the Frame?

If you have a broken or deteriorating window, you’ll undoubtedly be looking into types of window replacement. Depending on the condition of your windows, you will have different options open to you. If your frames are in good condition, you can replace the window without replacing the window frames – this is known as a pocket window replacement. However, if your frames are aging, it will be best to opt for full frame replacement windows.

We’ll take a look at the different replacement window options, their pros and cons, and when to choose each kind of replacement below. 

Choosing Window Replacements

When your windows need replacing, it can be a chance to fully embrace the change. You can pick a new style of window, one that fits your tastes or the design of your home better. In addition, you can pick a more efficient, insulating window replacement, one that performs better and lowers your bills.

On the other hand, all the options available can be overwhelming and it can be time-consuming trying to find the best choice. For most people, it’s less of an opportunity and more of a hassle. Potentially an expensive hassle. Many people just want the quickest, cheapest option. Their instinct will be to get a like-for-like window replacement and be done with it.

Most people only know of full frame replacement windows, but did you know there could be an easier way to replace your windows where you keep the existing frame? A pocket window replacement allows you to replace your window without having to replace the window frame.

It’s not suitable for every situation, but it is a more cost-effective solution if your window frames are still strong and stable.

What Is a Full Frame Window Replacement?

A full frame replacement involves taking out the entire window and frame. Even the trim is removed, everything right down to the walls of your home.

It’s a complete fresh start for your windows, allowing you to change the material, appearance and style of your window.

Pros of Full Frame Replacement Windows: 

  • You will be left with a far more energy efficient window. Firstly because the sash-to-frame fit will be a lot closer (as they were manufactured to match), but also because it allows the chance to add insulation around the window opening.
  • It exposes the rough opening of the window, allowing a chance to inspect it and address any issues, like damp or rot, that might shorten the life of your window otherwise.
  • You will keep the full breadth of the window glass.


  • It is more expensive as it is a more complex job. It isn’t just the cost of the extra frame – the work takes more time, and potentially more manpower, all of which contributes to an increase in price.
  • It is more disruptive. 

What Is a Pocket Window Replacement?

Also known as an insert window replacement, a pocket window replacement is when only the interior frame (or sash) of the window is removed. A new window is then ‘pocketed’ into the old frame. 

Pros of a Pocket Window Replacement: 

  • It is cheaper – not only does it involve less materials, it’s also a quicker job.
  • If your window frame is still fully functional, it is less wasteful.


  • It can mask potential issues in the frame, such as wood rot or damp in the rough opening.
  • Even if your frames are stable at the time of the pocket replacement, they will still need replacing eventually – potentially long before the insert window does.
  • By inserting a new frame into an existing frame, you will lose some of the glass size of the window. This will affect how much light the window lets in.

When to Choose a Full Frame Window Replacement

Obviously, if you want to dramatically alter the appearance of your windows then your only option is a full frame replacement. If you want to switch from casement to box sash windows, or similar, even if the window is the same size, a new frame will be necessary to house the opening mechanism.

However, appearance isn’t the only deciding factor. You can only choose an insert window replacement if your existing frames are still in excellent condition. If your frames are even slightly cracked, chipped or warped, they could be compromised and it wouldn’t be worth using a pocket replacement, as the frames would need to be replaced soon enough anyway.

If there is rot present anywhere around the window, including the frame, sill, trim or casing, then you will have to go for a full frame replacement. The rot will weaken the frames, and could spread to the insert window. A pocket window replacement on a less-than-perfect-frame is a waste, as it will have to be fully fixed later.

When a window gets damaged, the prospect of replacing it can be daunting. Choices will need to be made, money will need to be spent. With a pocket window replacement, you have the option to spend a little less, while still keeping your home safe and warm. However, if your window frames aren’t good as new, it is best to opt for a full window replacement. This will allow top performing windows in terms of insulation and security, and ensure you don’t need to do more work in the near future.

We offer a wide variety of high quality replacement windows. From our top of the range, high performance JELD-WEN windows to our own timber windows & aluminium windows, there’s something for all properties. Get in touch with any enquiries.

sound waves

Which Type of Glazing for Noise Reduction?

There are several different sorts of glazed window available. There are traditional single-paned windows, which comprise just the one sheet of glass. Then there are the popular double-glazed units, which sandwich a layer of inert gas (or vacuum) between two glass panels. If you want to go even further, there are even triple-glazed windows which add another layer of glass (and another layer of inert gas).

The more layers, the more thermally insulated it is. But what if you’re concerned with sound pollution, too? Well, the good news is that certain sorts of window will offer considerable protection from unwanted noises. But which is best? And what alternatives are available?

Which Window Glazing is Best for Noise Reduction?

Will Double and Triple Glazing Reduce Noise?

A double-glazed window will reduce noise more than a single-glazed one. Triple glazing tends to be no more effective than double glazing when it comes to sound insulation, if you are keeping the thickness of the window the same. Thinner sheets of glass will vibrate more easily, and if the volume of air is the same, then there’ll be no real difference in sound conductivity. In practice, triple glazed windows contain more glass – and since sound travels more easily through solids than gases, they conduct noise more easily.

Will Secondary Glazing Reduce Noise?

If one window will reduce noise, then two windows placed back to back will reduce it even further. In fact, secondary glazing is even more effective when the glass used is of a different thickness. It’ll resonate at different frequencies, causing a more complete deadening effect.

Window Glazing Costs

Different sorts of glazing will incur different costs. Triple-glazed windows are far more intricate and complex than double-glazed ones, which tends to mean more expense. You can expect to pay around 50% more for a triple glazed window than a double-glazed one.

The material used for the frame will also influence the cost of the window. Aluminium windows and timber windows tend to sit at the more expensive end of the scale, but they do look better than uPVC ones – which, while more affordable, aren’t quite as strong, and thus need to be made thicker. When you’re making this decision, you should factor in the money that you’ll save over time as your energy bills go down.

Generally speaking, the more windows that you elect to have fitted at the same time, the more economical things get. Installers must factor in the time spent travelling to and from your property, and thus getting everything done at once tends to be cost effective.

How Can I Soundproof a Window?

window with patterned heavy curtains

Of course, replacing an entire window can be very expensive. If you’d like to reduce the volume without spending a packet, then there are a few simple steps you can take.

Firstly, you might dress your windows with heavier curtains – and then, crucially, draw them. You might then examine the edge of the window for any gaps, and seal them. Finally, you might consider covering the window with a screen – or even secondary glazing. If you live in a conservation area, this latter option might make a fantastic alternative to traditional double-glazing.


Do Glass Windows Protect against UV Rays?

Ultraviolet radiation refers to light that is at a higher frequency on the electromagnetic spectrum than the light we can see. It’s notorious for being bad for your skin and eyesight, for being associated with various sorts of cancer, and for causing sunburn.

If you’re shopping for a new window, these are all things which should concern you. Does ultraviolet light pass through glass in the same way that visible light does? And, perhaps more importantly, can you get sunburnt from sitting beside the window? These are the questions we’ll be tackling in this article.

Do UV Rays Go Through Glass?

The answer is a little bit complicated. Not only are there different sorts of glass with different properties, but there are different sorts of UV light, too.

Shorter-wavelength UV-B rays are easily excluded, but longer-wavelength UV-A rays can easily pass through a normal glass window.

If you’re wondering, there is such a thing as UV-C – but these wavelengths tend to get blocked by the atmosphere before they even strike the surface of the planet. So, that’s one less thing to worry about!

Can You Burn Through Windows?

Common glass windows in your car, home, office and in our range will block almost all UV rays that reach the Earth. Glass does struggle with UV-A rays as mentioned before, so whilst you may not feel burning, the UV-A rays can still cause damage to your skin. However, in the UK, you’re going to have to be sat by a sunny window for a long time for that to happen. If you are going to be by a window on a sunny day for hours and your skin is quite sensitive, then some sun block won’t hurt.

Sunburn, moreover, is just one type of skin damage that can result from excess UV exposure; certain sorts of people will be vulnerable to increased freckling and photodermatitis (a skin condition exacerbated by exposure to light).

For an average person in the UK, you really don’t have to worry about burning through your windows on a sunny day. But UV radiation and its effects on the skin aren’t to be ignored. Take care in sunny conditions and always err on the side of caution. Remember also, that you can get sunburnt on a cloudy day.

Of course, some of us deliberately seek out the sun in pursuit of a healthy-looking tan. We’ve covered how windows can contribute to tanning in a previous blog, so be sure to check that out.

Another factor we haven’t considered is that the UK doesn’t receive all that much sunlight – so unless you’re sitting in a conservatory for hours on the south side of a building, you’re unlikely to suffer much. While obviously being true, this fact doesn’t stop UV rays from being damaging. If you’re fortunate enough to work in a greenhouse all day (or unfortunate enough to work at a computer besides a sun-facing window) then it’s important that you aren’t blasé about the damage the sun can inflict. Draw the blinds (or apply some sun lotion) and give yourself peace of mind!

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Tree in a field on a sunny day

How to Recycle Window Glass

Glass recycling isn’t exactly a new idea. Hopefully you will have been using your local bottle banks for many years now, and recycling all your sauce jars and bottles wherever and whenever you can. But this isn’t the only sort of glass that can be recycled: the stuff in your window is just as amenable to being melted down, reformed, and ultimately reused.

Can You Recycle Window Glass?

There are a few differences between the glass in your windows and the glass that makes bottles. Window glass is treated using a special combination of heat and chemicals. This makes it more difficult to break, and also gives it a higher melting point. Moreover, when it does melt, those chemicals leak out – which if you’re creating new glass products designed for food and drink storage, is a considerable problem.

The long and short of all of this is that window glass can’t be mixed with general glass recycling. It can be either used to make more windows, or it can be ground into a powder and then used as a bulking agent in cement and concrete. This means putting in a special recycling bin. In the developing world, this requires infrastructure which simply isn’t yet in place. In the UK and Europe, however, the story is a little different. A Europe-wide project is currently underway, which aims to make the recycling of this sort of glass economically viable, and thereby spread the practice.

Recycling Glass Windows

So, you might be asking, how do I get rid of old windows? You have several options available, but the most straightforward is locate your nearest recycling centre and make a trip down there.

Where Can You Recycle Glass Windows?

The chances are good that you’ve a suitable glass-recycling facility within a few miles of where you’re now sitting. British Glass provide a useful tool which will help you to locate your nearest. Give them a call before you turn up, and check that they’ll take your window, and that they’re open to non-locals. You might find that you have other recyclable materials at home that can be disposed of on the same trip.

Re-using the glass

On the other hand, you might decide that you can re-use the glass elsewhere in your home. You might be able to extract the glass from your window and turn it into a cabinet, a tabletop, a picture frame, or even outdoor flooring. In the case of the latter, you’re going to be shattering the window into fragments, and leaving it to set on top of setting cement. When the whole thing is set, you can grind the thing down into a smooth, safe surface.

Obviously, this sort of thing is inherently dangerous, and requires that you take adequate precautions. Use protective goggles, gloves, and make sure that you sweep up any fragments or dust when you’re done.

Selling the Window

Of course, most of us will hesitate before going to all of this effort – particularly if we’re not all that creative. But you might find that someone else in your vicinity has a use for your old window, even if you don’t. Making a listing on a site like Gumtree or Facebook is free and may yield results. Perhaps someone needs a new window for their shed, or perhaps there’s a local artist who specialises in glass!


If you’re getting rid of your old windows and looking for new ones, check out our JELD-WEN brand range, our timber window range and aluminium window range. Just get in touch if you have any queries.

bow window

What Was Used in Windows Before Glass Was Invented?

While the modern window might seem like a pretty simple contraption, it’s actually made from dozens of carefully-engineered parts. Double-glazed windows are able to insulate far better than a single sheet of glass – but even that required hundreds of years of refinement and engineering before it could be made thick and flat enough to actually see through.

Before the earliest forms of glass came to be, a window would be a simple hole in the side of a building, over which could be hung crude animal-skin curtains at night-time. Not terribly comfortable! So how did the modern glass window come about?

When Were Glass Windows Invented?

Glass, as a material, is rare in nature. Usually, it comes in the form of obsidian – which is entirely black. Synthetic glass first came to be widespread in ancient Egypt and Mesopotamia in around 3500 BCE, and came to be used for vases and cups thousands of years after that.

Glass windows, on the other hand, came much later. The ancient Romans used them, sporadically, in the more upmarket villas and government buildings – though their optical qualities were far behind what we might expect today. In certain places, like churches, this difficulty became an opportunity: stained glass windows allowed for the depiction of certain religious scenes. In this setting, transparency didn’t matter.

The earliest forms of window glass were ‘broad sheet’. These were made by first blowing a tube of glass, and then cutting off one side and rolling the whole thing flat.

The difficulty of manufacturing glass windows made them something of a status symbol – and this continued right up to Tudor England, where only the wealthiest households could afford windows of a decent size. In Europe, the Italian renaissance left no aspect of culture or industry untouched. Windows there became taller and sleeker, and separated by mullions and transoms (the wooden crossbeams which run across the surface of a window). As time went by, these elements were made progressively narrower – so that more light could pass through the window.

The Sash Window

The 17th century saw the introduction of an entirely different sort of window: the sash window. This variety of window consisted of two moving panels, which could slide behind one another to create an opening. Windows of this sort needed to be made from ‘crown glass’: a more affordable material created by spinning discs of the stuff, and then cutting those discs into broad sheets.

Modern Windows

Today, our windows are almost universally made from machined ‘float’ glass. This process came about in the mid 19th century, and though it’s been extensively refined since then, the principles used today remain the same: the molten glass is poured into a bath of molten tin. The two materials are immiscible, meaning the sheet floats upon the molten tin as it cools (like oil might float on water). The result is a perfectly smooth sheet on both surfaces, which, after a little bit of extra treatment, becomes perfectly transparent.

If you are looking for quality windows, take a look at our range of JELD-WEN windows and our own timber & aluminium windows. Just get in touch with any queries – we’re happy to help.

Coloured wooden windows

What U-Value Should Windows Have?

When you’re shopping for a new set of windows, there’s one metric that you’re almost certain to encounter, and that’s the ‘U’ value. This number is a way of describing a window’s thermal efficiency, but what does it mean? What are the best U-value windows, and what’s the U-value of double glazing?

How Does U-Value Work?

Let’s start with some definitions. A U-value is a measure of heat energy moved through a given area of material in a given period of time. This might be a window, but it might equally be a wall or a door. It’s most often measured in watts per metres squared, when the difference in temperature between the two sides is one-degree Kelvin. Given that that’s a bit of a mouthful, we tend to say ‘W/m2K’ instead.

It’s important to note here that the U-value of a given window refers to its efficiency per square metre. So, two windows might have the same U-Value, but transmit heat at different rates because one is a different size to the other.

The lower its U-value, the better an insulator the window will be. If you’re aiming for the most thermally efficient house possible (as most of us are, cost permitting), you should almost always go for the window of the lowest U-value.

How Do You Calculate the U-Value of a Window?

If you’re buying a new window, you’ll be able to see its U-value advertised by the manufacturer. Unfortunately, calculating a window’s U-value yourself isn’t particularly easy, nor are your calculations likely to be totally accurate. However, if you’re determined to try and calculate the U-value of a window yourself, you can find out how here.

For example, not every glass panel is manufactured to the exact same standards, and what stacks up in a laboratory might not translate into the real world. While there are bodies like the BFRC (which we’ll discuss in a minute) there to maintain quality standards, it’s important to treat claims about efficiency with a degree of scepticism.

Secondly, the glass panel isn’t the only thing you need to consider – the window frame also conducts heat, and will contribute to the thermal efficiency of the window. While it’s possible to account for this in your calculation, given that the interior of a window frame is made from a range of different materials, doing so can be very difficult.

To comply with building regulations, windows (like every other element of your property) must meet a certain minimum U-value. In the case of a window, it’s 1.6 W/m2K. Double-glazed windows, filled with argon, are typically 1.4 W/m2K, while thicker triple-glazed windows can go as low as 0.7 W/m2K.

The British Fenestration Rating Council provide a colour-coded rating system to help homeowners distinguish between different qualities of window. Good windows which keep the heat in are rated A or above. Bad ones are related E or below. While this rating system is easy to follow, and will prevent buyers from making a mistake they’ll regret for years, it isn’t quite as specific as the U-value. As such, when you’re shopping, we’d suggest looking for the U-value and spending your money accordingly.

For example, Jeld Wen’s triple-glazed ‘Stormsure Energy+’ series of casement windows can have a U-value of 0.8, 0.9 or 1.0, depending on which options you select. Each window in the range, however, comes with the same BFRC rating of A+. So, if you want the absolute maximum thermal performance available, you’ll need to look beyond the lettered rating, and at the U-value.

U-Value: Double Glazing versus Triple Glazing

Given how effective double-glazing is compared to single-paned glass, you might suspect that adding an extra layer would improve things still further – and you’d be right. Triple-glazed windows are more effective insulators than their double-glazed counterparts.

That said, there are a few drawbacks to consider. Triple-glazed windows tend to be thicker, which means they’re not ideal for use in smaller frames. They’re also more difficult to manufacture, and as a result, more expensive.

Putting to one side practical considerations like these, there are a few instances where a triple-glazed window might not be as good a choice as its U-value might suggest. This is because of heat gain, or a lack of it.

As sunlight pours down onto your triple-glazed window, the heat won’t reach the interior as quickly as it might if the window were double-glazed. As such, south-facing windows which receive direct sunlight might be better suited to double-glazing than triple-glazing.

In Nordic countries where triple-glazing is widespread, there’s less sunlight, and so this issue isn’t as pressing. In the UK, it’s worth treating triple-glazing with a bit more caution. We’ve examined the thorny double-versus-triple-glazing debate in greater depth in a previous article, and if you’re considering going for triple-glazing, we’d suggest that you give it a read.

While U-value isn’t the only metric of a good window, it’s one worth paying attention to before you make your purchase. Generally speaking, the lower the U-value, the better. It’s worth investing more in a superior-quality window, as the extra cost is likely to pay for itself over the lifetime of the glazing. That said, thermal efficiency isn’t everything – if you’re not happy with the look of the window, or the warranty isn’t sufficiently long, then going for a super-efficient U-rating at all costs probably isn’t a sensible strategy.

Ready to shop for new windows? Take your pick from our JELD-WEN range, timber range and aluminium range. You can also get an estimated quote here.

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Condensation on window

What Causes Foggy Windows and How to Prevent It

Do your windows have a foggy appearance? Fortunately, as unsightly as it may be, window-fogging is a common phenomenon, and there are several ways of counteracting it, if not avoiding it altogether.

Why are My Windows Fogging Up?

In order to prevent windows from fogging up, you need to figure out what’s causing them to fog up in the first place.

Windows fog for several different reasons. All of them, however, can be reduced by the same phenomenon: airborne water vapour settling on a cold surface and condensing into tiny droplets.

These droplets diffuse light that passes through them, and thereby produce the ‘fogged’ effect.

Since glass is invariably among the coldest surfaces in the home, it’s here where you’ll first notice this fogging effect.

Windows fogging on the inside

Condensation on the inside of a window is caused by excessive humidity inside the home. You’ll notice this most often in winter, when the difference in temperature between the exterior and interior of the property is most pronounced. If you’re releasing a lot of moisture into the air by cooking or showering, then the problem is going to be even more apparent – which is why kitchens and bathrooms tend to be more affected than other rooms.

Windows fogging between panes

Double-glazed windows are formed of two glass panels, between which is sandwiched a layer of inert gas, typically argon. This gas is kept in place by air-tight seals running around the edges of the window. Should this seal start a leak, the gas will be able to escape.

This is usually noticeable when water-droplets appear the interior of the window, where they’ll condense. Manufacturers normally ship their double-glazed window with drying agents on the inside, which remove any moisture trapped during manufacture. If there’s a leak, however, these drying agents begin to lose their efficacy.

What Keeps Windows from Fogging Up?

There are two main ways in which you can prevent windows from fogging up.

  1. Raise the temperature of the glass so that water can’t settle.
  2. Reduce the amount of moisture in the air.

Since we want our windows to be as energy-efficient as possible, and there’s nothing we can do to alter the humidity outdoors, we should resign ourselves to the fact that fog on the outside of your window is a natural and largely unavoidable phenomenon. Fog on the inside of your windows, on the other hand, can often be corrected through proper ventilation.

A new window will be more efficient at keeping out drafts than an old one – and this can interfere with a building’s ability to properly ‘breathe’. This is why many new windows come with some form of ventilation built-in – most commonly, ‘trickle vents’, which constantly let in a steady stream of fresh air in the home (and let moist air out).

Other rooms may benefit from extractor fans – namely the kitchen and bathroom.

When you’re boiling pasta, crank the extractor to its maximum setting; it’ll suck up all the steam you’re creating. This will prevent water vapour from spreading throughout the room.

Similarly, an extractor fan near your shower will reduce moisture in your bathroom.

If your windows are fogging up even in environments where you aren’t creating moisture, you might consider investing in a dehumidifier.

Excessive airborne moisture doesn’t just cause your windows to fog up – it’ll also accelerate rot and other structural problems. This means you need to treat it seriously, even if you don’t need to see out of the window in your bathroom!

Do Foggy Windows Need Replacing?

If your windows are fogging up, then you might wonder whether your windows need replacing. If fog is forming between the panels of a double-glazed window, the answer is almost definitely yes. If this has happened, your window’s seal has been compromised and the unit will only continue to deteriorate over time.

You may be able to live with the problem initially, but eventually you’re going to need to get the windows replaced.

wooden windows

Argon vs. Krypton vs. Xenon in Windows

When it comes to energy efficiency, windows are notoriously vulnerable.  Given a chance, they’ll drain the heat out of your home and into the great outdoors, far faster than brickwork and doors.

Of course, this isn’t a new problem, but in recent years better solutions have entered the market.  Of these, double glazing is the best known.  In a double glazed window, two glass panels are placed parallel with one another, with a layer of insulating gas sandwiched in between.

The precise makeup of this gas has changed over the years.  When the technology first appeared in Victorian Scotland, manufacturers used ordinary air.  During the middle of the 20th century, manufacturing techniques became more sophisticated, and the air was replaced with a vacuum.  Inside a modern double glazed window, however, you’re likely to find one of three noble gases: namely argon, krypton or xenon.  Take a look at the periodic table, and you’ll find them stacked on the right-hand side.

But what are the practical differences between these gases?  Why is argon used in double glazing instead of air?

Why Argon in Windows?

Argon gas windows represent, in most situations, the optimal balance between performance and cost.  If you shop for double glazed windows, you’ll tend to find that they feature argon alongside low-emissivity glass, and thereby reduce heat gain during summer while keeping the interior cosy during winter.

Argon offers a thermal conductivity around a third lower than ordinary air, for only a marginal increase in cost.  Treated well, argon-filled double glazing will last for more than two decades, losing only a fraction of its performance over the years.

Are Argon Filled Windows Worth It?

In most cases, argon-filled windows are an obvious choice.  Having said that, some circumstances might call for a more expensive, high-performance gas.

Why Krypton in Windows?

Krypton represents something of a middle ground between argon and xenon.  It’s more expensive than the former, but less so than the latter.  It’s yet to overtake argon as the industry standard, on account of its higher price, but this might well change in the future, should manufacturing techniques become even more sophisticated.

Krypton-filled double glazing tends to be thin. Indeed, if krypton is used in a wider gap than, say, 20mm, convection currents will begin to form that transfer heat from the interior of the window to the exterior.

In old buildings, cavities were filled with single-paned windows, meaning there might not be sufficient room for a thicker argon-filled window.  You might therefore consider krypton-insulated windows as a means of preserving the aesthetic of the building while enhancing the insulation.  It’s worth considering the potential difficulties inherent in obtaining planning permission for a double glazed window in a period property, since the difference in pressure between the two sides will generate a bowing effect on the glass.  This can undermine the appearance of the property from the outside.  That said, this drawback is common to every sort of double glazing – not just krypton-filled windows.

If you don’t have any such space restrictions to worry about, then you might cram multiple layers of krypton gas into the same window.  Triple glazed krypton-insulated windows incorporate three panes of glass, the middle of which will interrupt the convection currents we’ve just discussed.  In the UK, such windows are installed only rarely, since temperatures don’t often dip low enough to justify them.  If you’d like to go down this route, however, krypton is worth considering.

Are Krypton-Filled Windows Worth It?

It’s difficult to state with certainty whether krypton-filled windows justify their price point, as the answer will depend on your aims.  Most in the building industry will view them as an extravagance, but if you consider energy efficiency to be important, krypton might well prove tempting.

Why Xenon in Windows?

Let’s take a moment to consider trends in the world of architecture.  A modern skyscraper has a surface area made almost entirely from glass, and they’re not an exception – courthouses, swimming baths, service stations and office buildings across the country are increasingly transparent.  The advantages of this approach are obvious: glass allows more natural light into an interior, and helps us to see the world outside.

But how can architects incorporate such large expanses of glass without compromising the energy efficiency of the building?  One answer comes in the form of xenon.  Xenon-filled windows are a relatively recent innovation, and sit at the forefront of glazing technology.  They’ll insulate wonderfully.  But this performance comes with a price tag to match.

Xenon gas windows are therefore permitted in exceptional circumstances only.  If a business wants to achieve LEED certification for their headquarters, for example, then xenon might just be a way to do it.  Some residential circumstances might also warrant the use of xenon-filled double glazing – but these are rare.

Are Xenon-Filled Windows Worth It?

The short answer is: probably not.  Xenon’s eye-watering price puts it out of reach of all but the most ambitious homeowners.  That said, if you’re planning your dream property, and you’d like to incorporate a lot of glass, then the performance of xenon might make it worth considering.

So What Should You Choose for Your Windows: Argon, Krypton or Xenon?

When it comes to energy efficiency in double glazed windows, the three gases could accurately be labelled as ‘Good, Better and Best’.  A denser gas will perform better as an insulator, but this performance comes at a cost.

Your choice of window will, to a large extent, depend on your personal tastes and circumstances.  For most of us, the insulating qualities of argon will be more than sufficient, and the cost of the more effective materials will outweigh their advantages.

Looking for new windows for your home? Browse our sliding sash or conservation windows or find out about our handmade bespoke windows.

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Plant on a window ledge

Types of Glazing

When you think of glazing you might just think “single”, “double”, and “triple” – but there’s much more to window technology than the number of panes.

Here’s a rundown of the most common types of glazing you’ll find used in windows today.

What is Annealed Glass?

Annealed glass is slowly-cooled after first being formed.  It’s left to rest at a temperature where it becomes too hard to manipulate, but soft enough for any stress points to melt away.  This steady, consistent temperature at the earliest stage helps the glass resist shattering and mechanical shock during installation.  Annealed glass is a commonplace, inexpensive and tough material, but it isn’t quite as durable as tempered glass.

What is Tempered Glass?

Tempered glass undergoes a final stage of heating to make it even stronger.  While annealed glass might shatter into large, jagged fragments should it break, tempered glass will instead shatter into tiny pieces.  As such, it can be safely used in tabletops and flooring without fear of serious injury should it break.  It’s also commonly used in public facilities such as bus stops.

What is Safety Glass?

Safety glass reinforces each pane with a thin layer of tough plastic, like polyurethane.  This holds the glass aloft so that even if it does break, it won’t fall to the floor.

What is Low-E glass?

Low-E glass (or low-emissivity glass) reflects far more heat than ordinary glass.  As such, low-E glass is a sensible choice for homeowners looking to control the interior temperature of their property.  It’s coated in a microscopically-thin layer of metal that bounce the sun’s rays back the way they came.  Low-E glass comes in two types:  passive, which is built to keep heat in during winter, and solar-control, which keeps heat out during the warmer months.  Low-E double-glazed windows tend to incorporate a combination of the two.

As an added benefit, low-E glass will also prevent a majority of ultraviolet rays from entering the building, which will protect upholstery and carpets from fading.

What is Frosted Glass?

Frosted glass is covered in tiny bumps which effectively diffuse light rays.  This means specific objects can’t be seen through the glass, although light will still shine through.  This effect can either be created at factory level by blasting each panel with high-velocity grit, or in-situ, by spraying a special substance directly onto the window.

What is Self-Cleaning Glass?

The idea of glass that cleans itself might seem like something out of science fiction, but the technology has actually been around for more than a decade.  It works via a coating of titanium dioxide, which is used in a range of unusual places – from white paint and food colouring to suntan lotion.  When it’s placed on windows, it’ll respond to sunlight by transforming surrounding water molecules into hydroxl radicals, which will break down any surrounding organic matter (like the microscopic gunk from which dirt is made).  Once broken down, these tiny quantities of dirt are easily washed away by rainwater.

What is Noise-Control Glass?

One of the chief virtues of double glazing is its ability to reduce noise pollution.  The layer of vacuum (or inert gas) which sits between the two panes will reduce the amount of noise transmitted by as much as three quarters, which in most cases is more than sufficient.

That said, if you’ve recently bought a home beneath a flight path or next to a train line, you might want protection that’s a little more substantial.  This can be achieved by placing an additional layer of special acoustic-dampening plastic between the window panes.  This plastic will absorb the sound waves, thus preventing those vibrations from finding their way into your home.

What is Fire-Protection Glass?

Fire-resistant glass works by weaving a layer of special, hard resin between the panels.  It’ll vastly increase the breaking point of the glass, up to more than 800°C (ordinary glass will begin to break down at around 260°C).  This difference can buy valuable time that might make the difference between life and death. As a result the technology is particularly worthwhile in public buildings with interior windows, and in densely-packed streets where fire might otherwise spread quickly.

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Spacious room with a large window

What Is Low-E Glass?

Ordinarily, glass will allow solar energy to pass from one side of the window to the other.  This includes the relatively narrow spectrum of visible wavelengths, as well as those higher and lower wavelengths (known respectively as infra-red and ultra-violet light).

This is bad news!

Ultraviolet light has a habit of bleaching materials it comes into contact with.  Fabrics and wallpaper will fade much more quickly if they’re exposed to UV for a significant period of the day.

Infra-red light poses a different problem, in that it’s transmitted into the building as heat.  If you’re looking to keep cool during a blisteringly hot summer’s day, you’re going to struggle – you might even be tempted to draw the curtains in order to keep the sunlight out.

Low emissivity glass (or low-E glass) comes with a special coating that’s designed to act as a filter, allowing visible light through while excluding the superfluous wavelengths to either side.  This will allow your interior to enjoy the benefits of more light, without the downsides posed by ultraviolet and infra-red.

How Does Low-E Glass Work?

When heat or light strike a surface, that surface will absorb a portion of that energy and re-radiate it.  How large a portion this might be will depend on the surface in question.  If you’ve sat in a car with black leather seats on a summer’s day, you’ll know that dark materials tend to absorb and radiate more energy than reflective ones.

The amount of energy radiated by a surface is known as its emissivity. Glass, unfortunately, is naturally high in emissivity.  The more we can reduce this, the better an insulator our glass will be.

On the surface of each pane of low-E glass is a microscopically thin coating that is designed to reflect infra-red rays.  This coating can be made from silver, or a variety of other metals, but their purpose is always the same: to deflect heat away from the glass.

Types of Low-E Glass

Low-E glass comes in two different varieties, and it’s produced using two different techniques:

  • A passive Low-E coating is built to contribute to the amount of heat within a home, preventing energy from leaving and thus lowering the heating bill.
  • A solar-control low-E coating works in the opposite way. It reduces the amount of energy entering the home, helping to keep it cool.

The right type of low-E glass for you will depend on the location of the building.

How is Low-E Glass Coated?

Each type of glass can be coated using one of two methods:


This process emerged in the 1970s.  It is applied to the glass shortly after production.  The coating fuses neatly with the hot glass before the latter has a chance to set, and stays that way for the entire lifespan of the window.  The glass is then cut to size and shipped.

Magnetron Sputter Vacuum Deposition (MSVD)

This process came a little bit later, in the 1980s.  It’s slightly different in that it’s applied to the sheets of glass after they’ve been cut to size, using a vacuum chamber and magnets to apply the coating at room temperature.

For many years, passive coatings were produced using the pyrolytic method, and solar-control coatings using the MSVD method.  More recently this line has begun to blur.

What does Low-E Glass Look Like?

So what effect, if any, does a low-emissivity coating have on the appearance of the window?  Since there are many different types of low-E coatings, and they can be applied at different thicknesses, it’s easy to be misled by reports of a set of ‘tinted’ low-E windows which block out certain colours, and distort the view of the exterior.

If, however, you want to ensure you don’t get any nasty surprises, it’s worth inspecting the sort of low-E glass you’re considering before making your purchase.

Low-E Glass U Value

The thermal performance of windows is typically measured using the U-value.  This number refers to the amount of heat loss the glass permits per a given area.  According to the U-value, low-emissivity windows tend to be twice as efficient as their plain glass counterparts – but it’s important that an impartial initiative backs up the manufacturer’s claims.

Low-E Glass UV Protection

Naturally, the U value figure doesn’t cover the UV light that low-E glass will block.  Depending on the strength of the coating, low-E glass can prevent anywhere between 80% and 99% of ultraviolet light from entering the home (compared with around 60% by a standard window).  This extra protection is especially worthwhile if the sunlight entering a window is immediately falling on a set of curtains, a fabric-covered sofa, or a prized rug.

Many of our windows are supplied with low-E glass as standard, including our sliding sash windows and our casement windows. View our full range of JELD-WEN windows and timber windows, or get in touch with any enquiries.

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