sunshine through window

Can You Tan Through Windows?

For many people, one of the best things about sunlight is the fact that prolonged (though careful) exposure will result in a healthy-looking glow.  It’s a big reason why holidays in the sunshine are so popular.

Unfortunately, unless you lead a particularly active and outdoor lifestyle, the chances are that you’ll get most of your sunlight through a pane of glass.  Which raises a question:  is it possible to get a tan through a window?  The answer – in short – is no.  In order to understand why, it’s important to understand exactly what tanning is, and what influence a pane of glass might have on it.

What is tanning?

The human body is remarkably good at adapting to new stimulus.  When we’re exposed to a new sort of harmful virus, for example, our immune systems will react by dispatching hordes of antigens to deal with the problem.

The same is true of ultraviolet radiation.  When we’re exposed to it, a specialist type of skin cell will react by producing melanin – the substance that gives your skin its pigmentation.  The more melanin in your body, broadly speaking, the better protected you’ll be against ultraviolet radiation.  This production tends to be triggered by UV ‘B’ exposure, and will result in increased melanin production a few days after you’ve been exposed. This will last for a few weeks or in some people, even longer.

The second process which causes tanning comes as a result of stress on your existing melanin, which will darken in response to UV exposure – and specifically to UV ‘A’ exposure.  This sort of tanning comes about almost immediately – but will disappear almost as quickly.

Of course, genetics also play a key role in determining melanin production – if you’re a red-headed, fair-skinned person whose ancestors came from the freezing Scottish highlands, you’ll likely burn a great deal more easily than a naturally olive-skinned person whose ancestors lived in Southern Spain.

Why do windows prevent tanning?

A set of double-glazed windows will act like a layer of sunscreen, or the o-zone layer which surrounds the planet.  Some ultraviolet light will get through – but only the least harmful wavelengths, and only in very small quantities.  This means, effectively, that we won’t be able to tan very easily – if at all.

That said, this shouldn’t imply that we need grant ourselves carte blanche to soak up the sunshine from behind a pane of glass – it’s surely no coincidence that the majority of skin cancer diagnoses in the US occur on the left-hand side of the body – the driver’s side.

Can you absorb vitamin D through windows?

Another benefit of UVB rays is that they promote the production of vitamin D – which is crucial for bone growth and other body functions.  Since most glass windows block this frequency, it’s crucial that you get out into the real sunshine when you can – just be careful to only stay in the sun for as long as you need to absorb vitamin D – you do not want to burn!

Exactly how long this will take depends on your skin type, the time of year, and where you are in the world. However on an average hot summer day, a very fair skinned person will only need about 4 minutes sun exposure to absorb the right amount of vitamin D. Very dark skinned people will need about 20 minutes.

wooden windows

uPVC vs. Timber vs. Aluminium Windows

If you’re looking to improve the thermal efficiency of your home, then you’ll want to ensure that your windows are up to the required standard.  Windows are a notorious weak-point in many buildings, by simple virtue of the fact that they’re thinner and more heat-conductive than the surrounding walls.

Windows come in a number of different forms.  Some of these differences can boost the insulating performance of the window – double-glazing, for instance, sees two panes of glass placed parallel to one another on either side of a layer of vacuum, inert gas or dehydrated air. This significantly increases the window’s ability to retain heat.

As well as the glass that goes into the window, however, we should also consider the materials which comprise the frame.  Generally speaking, windows are built either from uPVC, timber or aluminium.  Each of these materials has their merits – and your choice will hinge upon the building you’re installing them into, as well as your personal taste.  Let’s examine the options in closer detail.


uPVC is an inexpensive plastic that’s found in white window frames across the country.  It offers excellent insulation and demands relatively little care and attention.  uPVC tends to cost far less than aluminium or timber, and is very easy to maintain.

That said, when we consider that these materials contribute to the value of the property they’re installed into, this economy often proves a false one in the long term.  While uPVC might not require cleaning and re-finishing in the same way that wood does, it’s got a much shorter shelf-life, and will not boost the value of the property in quite the same way.

Another significant weakness of uPVC is that it’s significantly weaker than the other materials.  This means that plastic frames must be made much thicker than wooden or aluminium frames in order to offer the same degree of performance.  The result is a window with a much smaller amount of glass, which in turn will reduce the amount of light in the interior of the building.

uPVC windows are a good choice for those looking for effective insulating performance for little hassle, at a reasonable price.  In the long term, however, their energy efficiency tends to suffer in comparison to the other materials available – and their look is not one that many homeowners will appreciate.


timber window

Timber window frames are a popular choice among those looking to invest in the outward appearance of their property.  Aesthetically, they offer a great deal more than their plastic counterparts, and, since every piece of wood is different, each wooden window is utterly unique.

Wood is naturally very good at insulating heat, which makes it an excellent choice for homeowners looking to save money during the winter.  Even inexpensive glass will perform well in a wooden frame.

Timber also offers a great deal of flexibility once it’s been installed.  The wood can be given a range of different finishes, each of which will have a profound effect on the way it looks in the end.  A coat of wax will penetrate the surface of the wood, helping to protect it from water damage as well as emphasising the qualities of the grain. A coat of paint, on the other hand, will afford homeowners the ability to create a window of any colour they like.

Of course, all of these virtues come at a price – wooden windows tend to be more expensive than uPVC.  They also demand more frequent maintenance if they’re to look and function their best.  They will, however, repay this investment by boosting the value of any property they’re installed into – and they’ll last a great deal longer.


aluminum sliding doors

The chief virtue of aluminium is its strength.  This allows for a slimmer frame, and a greater glass surface area.

Another advantage of aluminium is its durability.  Once it’s been powder coated a certain colour, it will be well-protected against rust and discolouration.  Moreover, you won’t need to re-apply the finish every few years in the same way that you might with a wooden window.

Being recyclable, aluminium is far more environmentally friendly than uPVC.  The energy required to produce an aluminium window is far below the cost of the raw materials, which makes it an excellent choice for those looking to reduce their carbon footprint.

Aluminium has considerable downside, though, and that’s its weakness as an insulator.  If you’ve ever held your bare hands against a metal surface on an especially cold day, you might recognise this phenomenon.  In modern frames, however, this problem is addressed with the help of a layer of insulating material on the interior of the frame.  And since metal frames are stronger, they’re able to hold thicker glazing with a narrowed frame – which can actually lend them an advantage in terms of efficiency.

In conclusion

Your choice of window will be largely informed by the surrounding building.  If you’re buying for a period cottage, for example, then you won’t want to ruin the look with the addition of a modern aluminium frame.  On the other hand, if you’re shopping for a contemporary house or apartment, then metal frames might match nicely.

Your personal taste will also be crucial when you make your choice.  If you’re really sold on the appearance of wood, then go for it.  However, be sure to consider the other windows in the building when making your decision, as you’ll want the entirety of your exterior to be consistent.

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

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water condensation

Why Does My Double Glazing Get Condensation On the Inside?

This can be a worrying find, but the good news is that condensation inside windows actually indicates that your windows are working as they should. In fact, you’re as likely to get condensation on new windows as old windows, and new windows may even increase condensation, since they should reduce draughts in the home.

That said, condensation on the inside of windows is something we should try to reduce, since it can damage window frames. Plus, who wants wet window ledges? It’s also indicative of a bigger problem – excessive moisture in the home.

Condensation between double glazing panes is a real problem and indicates a broken seal that will need fixing or replacing – but we will discuss this further on. For now, let’s look at why you get condensation on the inside of a window in the first place.

Why do you get condensation on the inside of a window?

One of the main advantages of double glazing is its ability to prevent heat from moving from one side of the glass to the other. It does this by sandwiching a vacuum (or a layer of inert gas) between two sheets of glass. When heat energy builds on one side, it has trouble passing through this inner layer, and so instead is conducted back into the room.

This prevents heat escaping, and will reduce your energy bills, but in doing so it will create a considerable difference in heat from one side of the glass to the other. It’s this difference that creates the conditions for condensation.

Cold air contains less energy than warm air, and it’s less capable of keeping water vapour in its gaseous form. This means that the air inside your home will be damper than the air outside. When this air hits a cold surface, like a window, it will lose the energy necessary to hold onto the airborne water, and so that water will be deposited. Over time, this effect causes the build-up of water condensing on the glass.

In short, condensation is warm moist air that turns back into water as soon as it hits a colder surface that it cannot pass through.

Where does condensation happen in the home?

You may notice condensation happening in certain rooms of the house:

  • The kitchen
  • The bathroom
  • The bedroom
  • The utility room

Cooking, showering, bathing, laundry all create substantial moisture which unless you keep the rooms very well ventilated, will settle on the windows. This probably isn’t surprising. What is puzzling is why we get condensation on bedroom windows, since we’re probably not cooking or showering in there.

During the day we move around the house but at night we’re confined to one small space for 8 hours or more, often with the door closed. The water we lose through breathing over those 8 hours builds up as moisture in the air. As we tend to keep bedrooms a little cooler than the rest of the house, the surface of the windows will be colder. The moisture will condense into water as it hits the cool surface of the windows.

Why is condensation bad?

Condensation can reduce the lifespan of a window, as it’ll encourage the growth of mould which can damage the frame. It can also be taken as evidence that the humidity inside your home is excessive – which can be a health concern.

How do you stop condensation on windows?

To prevent condensation settling on windows we need to take steps to reduce the amount of condensation in the home generally. Ideally, we want humidity levels to be at around 50%. In order to achieve this, we might try the following:

How To Reduce Condensation In The Home

Laundry drying outside
Dry Laundry Outside When Possible

There are many steps you can take to reduce condensation in the home:

  1. Ventilate Rooms

    Aim to open windows for about 20 minutes daily (yes, even in winter!) This will allow the damp air to escape and (unless it’s especially humid outside) dry air to replace it. Installing trickle vents can help reduce condensation too.

  2. Use an Extractor Fan

    If you’re cooking or especially showering, an extractor fan will remove damp air before it can settle on surfaces and cause problems.

  3. Use a Dehumidifier

    If the steps above don’t remedy the problem, or at least don’t sufficiently reduce condensation in the home, you may want to invest in a dehumidifier, which will extract moisture from the air.

  4. Don’t Dry Laundry Inside

    Drying wet clothes inside significantly increases the amount of water vapour in the air. The water has to go somewhere, after all. If drying laundry outside isn’t an option, ensure the space around your laundry is as ventilated as possible.

  5. Rearrange Your Houseplants

    Did you know that the more houseplants you have, the more moisture you’ll find in the air? Try moving your houseplants outside during the winter or choosing plants that absorb humidity, such as ferns, palms or cactus.

Manage other humidity sources

When you’re taking steps to guard against excess humidity, you’ll want to consider the things that can contribute to it. One of the most obvious causes are the living beings which inhabit a house – each of which, be they humans, dogs, cats or guinea pigs, will emit water vapour over the course of the day. Paradoxically, you might also encounter an uptick in humidity when you return from a spell away – as an empty house will be unheated, and therefore prone to absorbing moisture, which will be released when the heat rises again.

Do double glazed windows stop condensation?

Whilst condensation can be worse on single glazed windows (due to the internal surface of the window being much colder than the internal surface of a double glazed window) replacing single glazed windows with double glazing is not enough to eliminate the problem. The reason being is that although the inside of your new windows will be warmer, they will simultaneously eliminate draughts. This will reduce ventilation, and contribute to the build-up of moisture.

Acute causes of condensation on windows

If your condensation has appeared almost overnight, then you might be wondering what could possibly have caused it. There are several potential short-term contributing factors.

How Does Winter Cause Condensation?

When the weather outside gets cold, the chances of condensation occurring increase substantially. At the start of winter, it is therefore worth taking preventative steps before the condensation has a chance to develop.

Why Do New Windows Cause Condensation?

Newer double-glazed windows are able to do their job much more effectively than old ones, so don’t be surprised to see more condensation after getting new windows installed.

Can Underfloor Heating Cause Condensation?

Radiators help warm air to rise and circulate, so if you’ve swapped out your radiators for underfloor heating, you might see an uptick in condensation on your windows.

What about condensation between double glazing panes?

So far, we’ve been talking about condensation on the inside of the glass – but what happens when vapour gets in between the window panes? This means that the window seal has sprung a leak, which has allowed water vapour to get in. The inert gases inside a modern double-glazed window contribute enormously to its ability to retain heat, so if yours is showing this symptom, it’s probably time to replace your windows.

For more information, take a look at our blog post on why condensation forms between window panes.

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

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Tree in a field on a sunny day

Why Does Double Glazing Help to Keep Us Cool in Summer?

Double glazing is found in offices, homes and government buildings across the world, thanks to its remarkable insulative properties.  It will considerably outperform a single, ordinary pane of glass in impeding the flow of heat, and for this reason it’s a weapon of choice for homeowners looking to reduce their bills during those icy winter months.

But does double glazing keep heat out as well as in?  The answer is yes: a less often-touted benefit of double glazing is that it’ll help keep your home cooler in summer – which is invaluable if we’re to get a good night’s sleep during those July heat waves.

sun through window

How does double glazing work?

Double glazing works by limiting the amount of heat energy that can transfer from one side of the window to the other through convection.  It does this by placing two separate panes of glass parallel to one another, and leaving an empty space in between.  When one side of the glass becomes hotter, its molecules begin to vibrate very quickly, causing a chain reaction that spreads across the solid glass.  But this heat energy is unable to pass through the empty space on the other side, since there are far fewer particles through which to transfer the energy.  The heat is thus slowed down.   This effect is even more pronounced in modern forms of double glazing, which substitute empty space for a vacuum, or an inert gas like argon.

How do I compare different sorts of double glazing?

In order to see how effectively your window will contain heat (and noise), check its energy efficiency rating.  This score is presented on a scale of A+-G, with A+ being the best and G being the worst.  While a window’s rating will indicate its real-world performance, this performance will be impacted if the window suffers damage over time.

When the seal around the edge of a double-glazed window breaks, the gas trapped inside will be able to escape.  This effect becomes especially obvious during winter, when water droplets begin to condense between the window panes.  This is evidence that water vapour has found its way in through a gap, which means that the gas inside your window has escaped.   This will vastly reduce its ability to repel (and contain) heat, and so the window will need replacing.  Fortunately, this sort of wear-and-tear takes many years to manifest, but with the right maintenance, the day of failure can be delayed considerably.

How else can I keep my property cool during summer?

Of course, double-glazing isn’t the only way we can prevent heat from entering our homes.  In hotter climates, it’s common practice for windows to be fitted with shutters, which block heat from entering the house.  For obvious reasons, this is less common in the UK, but we can apply the same principle and close our curtains or blinds when the sun is beating down on the sides of our houses in the height of summer.

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

Wooden windows with shutters

Why Choose Wooden Windows?

When it comes to making improvements to your property, windows are an obvious place to start.  By nature, they allow more heat to escape than the walls that surround them.  And once they reach a certain age, they’ll inevitably benefit from being replaced with new, more efficient ones.

But windows come in a variety of styles, using a variety of materials.  Of these, amongst the most popular is wood.  Though they command a higher price, wooden windows boast several virtues which set them apart from their metal and plastic (uPVC) counterparts.

wooden casement window


It’s worth starting with what might seem a disadvantage:  wooden windows will command a higher up-front price than uPVC windows.  What’s more, they require regular maintenance, which means investing in waxes, oils, and brushes.  You’ll also need to put aside the hours (or, more often, minutes) necessary to apply these things – or pay someone else to provide them.

Wooden windows, however, tend to work out cheaper in the long run, as they’re far more resilient than uPVC, and should last much longer.  That’s why most warranties for wooden windows extend far beyond those attached to their uPVC equivalents.

Energy Efficiency

As a rule, wooden windows tend to perform better when it comes to energy efficiency.  Their frames are stronger and more durable, which means that they’re able to support thicker windows without becoming excessively bulky.  This means that thicker double-glazed and even triple-glazed windows are feasible.


Perhaps the greatest virtue of a wooden window is its appearance.  With the right natural finish to emphasise the grain, the inherent qualities of the wood can make the difference between an exterior that looks the part and one that doesn’t.  By the same token, a coat of the right paint can have a similar effect.  By re-applying the finish, the look of the window can be preserved long into the future, and this in turn can help to boost the value of the property.  But this needn’t be a regular ritual – wooden windows can last for years without needing a second coat of finish.  By contrast, the finish of a uPVC window can never be restored – once it starts to degrade, there’s no way to turn back the clock.


As you might imagine, wood can be obtained at far less environmental cost than plastic.  Timber can be sourced sustainably, and there are bodies like the Forest Stewardship Council, which help consumers to identify responsible manufacturers.  If you’re looking to reduce your carbon footprint, a wooden window is a better choice than a plastic one.

In Conclusion

While uPVC windows might seem a tempting prospect in the short term – particularly if you’re looking to re

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

Windows with external shutters

Why Are Double-Glazed Windows Filled With Argon?

When it comes to thermal efficiency, windows are among the most vulnerable points in any home. It’s through these sheets of glass that so much of the heat we generate escapes into the outside world.  This waste places a considerable strain on both our wallets, and the environment.

Thankfully, certain sorts of window offer considerable protection against this loss of heat.  Of these, the most widespread is double glazing, which features in a majority of homes in the United Kingdom.  It works by placing two panes of glass parallel to one another in the frame – an arrangement which helps to impede the flow of heat from one side of the window to the other.

If you’d like to understand why this is so, then consider a frying pan on a stove.  While the pan itself might be scalding hot, the air just a few inches above is cool enough that you can hold your hand there.  This is because the metal of the pan is an excellent conductor of heat, while the air around it is a relatively poor one.  Double glazing harnesses this principle, and it’s been enormously successful in doing so.

How has double glazing been improved?

Since its invention, double glazing has been improved in several key ways.  Perhaps the most obvious of these is triple-glazing, which sees a trio of glass panels being used in place of a mere pair.  But triple-glazing is difficult to manufacture, and comes with its own downsides.

Other advances have come about from using thicker panes, and wider gaps.  Manufacturers can also choose to fill the gaps with insulating gases.   For a time, among the most popular option was a vacuum, which slows convection even more effectively than the dehydrated air it replaced.  In modern double-glazed windows, however, a different and quite specific filling is used.

Where does argon come in?

Inert gases like argon, krypton and xenon are more often used by manufacturers today.  Each offers considerable improvements in thermal efficiency and noise reduction.  Of the three, argon is the least effective – but it’s also the least expensive, making it a material of choice for modern window-makers.

Argon is heavier than air, and so provides superior insulation and sound-proofing characteristics.  It’s also far more resistant to the formation of condensation, and will corrode the surrounding window far less than its equivalents – particularly at the bottom of the window, where condensation tends to start forming.

Since argon significantly improves the insulating properties of a window, it’s a popular choice for large, wall-encompassing windows and French doors.   Since the glass is more efficient as an insulator, we’re able to use more of it.  This allows homeowners to create that sense of extra space without compromising on their heating bills.  If you’re looking to upgrade your existing windows, an argon filled double-glazed replacement makes a sensible choice: it’ll offer energy efficiency savings which more than justify its initial extra cost, within just a few years.

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

Delapidated windows

When Should You Replace Double Glazing?

Double glazing has helped make our homes more energy-efficient than ever before.  By trapping a layer of air between two panes of glass, we’re able to greatly slow the transfer of heat from one side to another.  This was the case when the technology was in its infancy, and it’s even more so now. Thanks to special metal-oxide coatings that can be applied to the glass panes, wider cavities filled with inert gas, and heat-conducting materials like aluminium being replaced by insulating plastic and wood, double-glazing has never been more effective.

But despite this, double-glazed windows have only a limited lifespan.  Fortunately, there are a few clear signs which indicate a double-glazed window has reached the end, and is in need of replacement.  Let’s examine them.


condensation on window

Temperature differences between the inside and outside of a window are guaranteed to occasionally produce condensation.  As moisture impacts the cold glass, it will condense into droplets.   If the window is double or triple-glazed, this effect will be even more pronounced, as the heat from the interior of a home will be prevented from migrating outward.  The result, particularly during winter mornings, is the distinctive sheen of condensation on the window’s exterior.

In the UK, we endure relatively high humidity and wet winters, which means that we see moisture forming in the corners of our windows from the start of September up until late March.  While this brings about a number of unpleasant side effects, like the appearance of black mould, it doesn’t indicate any deep problem with the window – in fact, it’s evidence that the window is working as it should.  If condensation should start to appear between the panes of a double-glazed window, however, then something has gone seriously awry.

When a sheet of double glazing is manufactured, special care is taken to ensure any moisture trapped inside the pane is removed.  This is done using a special substance known as a desiccate; most commonly the same silica balls that you might find shipped alongside a piece of electronic equipment.  These substances help to remove not only the moisture that gets trapped between the panes during manufacture, but also the moisture that might find its way through tiny cracks as the window ages.  This provides some measure of protection against leaks.

A well-manufactured window will last for a long time before such a leak occurs – and even when it happens, the leak will be small enough that the extra silica will remove the moisture as it enters- but a limited amount of desiccant can only absorb a limited amount of moisture, and sooner or later, trapped moisture will begin to appear.

The time this take tends to vary depending on the manufacturer.  A reputable manufacturer will put their money where their mouth is, and offer a guarantee.  This assurance offers buyers some protection against premature problems with their windows.  A ten year guarantee should be considered sufficient.

If your window is under guarantee, then you can stop worrying, as everything should be covered.  It is important that you don’t attempt to repair the damage yourself, as doing so runs the risk of invalidating the guarantee.

Once condensation starts to appear inside the panes of a window, there’s very little that can be done to remove it.  What’s more, this moisture means the inert gas that was once inside the cavity has vented out through the same leak the water vapour entered through.  This means that the double glazing is nowhere near as effective, and should be replaced.


When windows are first fitted, they don’t perfectly match the contours of the space they’re occupying.  Even if you’ve measured everything as precisely as possible, the tiny (and often microscopic) imperfections in the wall and the window will mean that tiny gaps are present – through which cold air can pass.

This means that when installing a window, we use a special expanding foam, which will puff up and harden, filling all of those gaps and providing a tight seal.  Over time, however, this insulating cement can degrade – meaning that re-applying it might resolve draughts.

In particularly old windows, the draught might enter from between the pane of glass and the window frame.  This might mean that the weather seal – the rubber surrounding the frame, which provides a tight seal when the window is shut – has degraded.  While it’s possible to replace these devices, their failure usually indicates that a window is past its prime – and possibly, that it’s been superseded by new and more effective double-glazed windows.

Physical damage


Windows endure an enormous amount of wear and tear, some of which may cause the window to stop functioning properly.

Tiny chips and cracks in the glass might be repaired through simple buffing, but if the damage is severe enough, the window will need to be replaced. As we’ve mentioned, even the smallest leak will allow all of the inert gas trapped between the two panes to escape.

The frame, too, might degrade over time.  Fortunately, this damage is far less likely to result in the entire window needing replacing.  Chips and scratches might just be cosmetic.  It might be repairable by a specialist company, but if it’s severe enough to cause draughts, then a replacement will be preferable.

So, should you replace your windows?

Having to replace your double-glazed windows might seem an irritating extra expense – but there’s a silver lining in the form of the increased efficiency that newer windows yield.  When you’re shopping for a replacement, be sure to check how long the guarantee lasts – reputable companies like Windows and More will be happy to offer guarantees of ten years.

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

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cracked double glazing

What Causes Double Glazing to Crack?

Spontaneous cracking is an occupational (although rare) hazard of many double-glazed windows – particularly those at the cheaper end of the market.  At any time of year, a window might suddenly decide to collapse inward, causing an unsightly (and heat-inefficient) shatter effect.

What causes this peculiar phenomenon to occur?  While it might seem like the window cracked on its own, there is always an underlying reason at play. In this article, we’ll shed some light on the subject.

cracked window

How does double glazing work?

In order to understand why a double glazed window might crack, it’s worth considering how double glazing is constructed.  Two sheets of glass are placed either side of a vacuum – or a layer of inert gas like argon – through which heat has difficulty moving.  This creates a barrier which helps to contain (or repel) heat, and thereby keep your home at a stable temperature – and your energy costs down.

A double-glazed window is a sealed unit, which means that the pressure within it is constant, in contrast with the air pressure on the other side of the glass.  This means that the glass will be under constant, very mild pressure.  You might notice the glass of a double-glazed window slightly deform inwards, depending on the pressure outside.  In most circumstances, the glass will be strong enough to withstand this pressure.  But in some cases, it won’t – and stress cracks in the window can appear.

It’s revealing that the peak time for double glazing breakages is during winter.  This is a time of year that we experience colder outdoor temperatures – and we try to compensate for this indoors by using central heating.  This creates a big difference in temperature on either side of the glass.

What factors increase the risk of a double-glazed window breaking?

Aspect ratio

Square (or even round) windows are at the lowest risk of suffering a break.  Why might this be?  The answer lies in flexibility. Shorter panes of glass have less opportunity to flex than larger panes.  A tall, narrow window, then, will be at the greatest risk of cracking.

Manufacturing error

As commonplace a technology as double glazing now is, it’s still something that requires precise engineering in order to get right.  There are many different practices and environmental factors at the point of manufacture which can produce short-lived windows.


Creating windows involves, inevitably, cutting glass, but it’s important that these cuts occur only precisely where they’re meant to. Even a tiny, imperceptible scratch at the centre of a pane of glass can create a weak point which the elements might later expose.  This risk is greater when the cuts required are more complex, such as in bevelled glass.

Temperature and humidity

We’ve already mentioned how breakages become more likely when the temperatures on either side of the glass contrasts greatly, but what about the temperature of the gas inside the unit?  If a double-glazed window is created on a hot summer’s day, when the atmospheric pressure is low, then it’ll be at greater risk during the winter.

The same is true of the moisture within the unit.  Double glazing manufacturers use a special substance known as a desiccant to absorb all of this moisture and prevent condensation droplets from forming inside the window.  But this process, too, changes the pressure within the window, and so windows created on hot, humid days will be at greater risk of cracking when the temperature drops.

Not all desiccants are created equally, and some manufacturers look to slash prices by opting for cheaper alternatives.  Such desiccants will absorb not only water, but large amounts of nitrogen – which exacerbates any changes in pressure.

Strength of the glass

Of course, the odds of a window cracking can be reduced if the glass is of sufficient strength.  A thicker sheet of glass will be far more resistant to stress cracks than a thin one, so it’s often worth choosing a 6mm pane instead of the more common 4mm. When making this decision, however, you should be aware of where the stress is likely coming from. That will depend on how your house is arranged.

In order to reduce the impact of these environmental factors, it’s vital that manufacturers employ environmental controls in their factories.  While it’s impossible to eliminate the problem altogether, it is possible to reduce the likelihood of a break to the point of negligibility.  A good manufacturer will offer a lengthy guarantee against (seemingly) spontaneous window breakages.

Heat coming from outside

When it comes to stress on a pane of glass, it’s useful to think not only in terms of quantity, but of concentration.  Dispersing heat across the glass will reduce the impact that a concentrated beam of sunlight might have.

In the UK,  sunlight comes from the south.  This means that during winter, south-facing windows are at greater risk of cracking.  Overnight, the glass will cool (in some cases to sub-zero temperatures) – and then a beam of sunlight will suddenly appear.  The centre area will experience a sharp rise in temperature – but for the corners, which are still in shadow, this rise will be much milder.  This temperature difference across the glass will place it under much greater stress, and increase the chances of the window cracking.

In order to disperse the heat on those cold winter days, it’s worth placing a pale-coloured blind or curtain inside the glass.  This will help to reflect heat back onto the glass, helping to more evenly distribute the heat.

Heat coming from inside

Winter is also a time where windows are expected to cope with large changes in temperature from within, as central heating kicks in.  The biggest threats to your windows from within come in the form of acute, local thermal shock; typically from a radiator or fireplace right next to your window.

If you’ve got an under-window radiator, then it’s worth providing some protection in the form of curtains which fall behind the radiator, and protect the window from thermal shock.  You’ll also want to ensure that there is adequate airflow to the window from the rest of the room.

Looking for new windows? View our sliding sash windows, conservation casement windows, or our high-performance casement windows.

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