Double Glazed Windows

‘Double glazed windows’, we’ve all heard the term and most people will have an idea of what they are but usually only in a fundamental or vague sense. The fact that there’s a vast array of window types, frame materials and types of glass available may come as a surprise for some customers and, at first, all that information may seem a little overwhelming.

The aim of this page is to shed some light on all the options mentioned above. We will go into the details that we believe you should know about the different types of frames, windows, and glass so that the choices you make about your own double glazed windows will be the best informed possible.

What are double glazed windows?

Let’s start by talking about how double glazed windows differ from the traditional type. Traditional windows are made with a single pane of glass fitted into a frame. That single pane of glass (which, in some cases, can be as thin as 3mm) is then all that stands between the inside of your house and the elements, offering very little insulation.

Double glazed windows differ in that they contain 2 panes of glass in a single frame. However, there is more to it than that.

The two panes of glass are actually part of a larger design called an insulated glass unit (IGU for short). An IGU is made up of the two panes of glass and a spacer bar separating them.

The spacer bar allows for a sealed off area between the panes that can contain air or some other type of gas, or even This layer of gas provides a far higher level of insulation and thermal efficiency when compared with traditional, single pane windows. Which means more of the heat from inside the house will remain inside and the cold can stay outside where it belongs.

The spacer also has a secondary function, and that is to absorb moisture that may somehow get into the void between the panes. The spacers are usually filled with a desiccant whose job it is to capture any unwanted condensation that might get in a result of a damaged or degraded seal.

So why choose double glazing?

What benefits do double glazed windows offer?

As we already mentioned above, double glazing offers much improved thermal efficiency, which in turn helps to lower your energy costs and contributes to protecting the environment. In summer they can reduce the amount of heat coming in from outside, thereby aiding your property in keeping cool.

In addition to these energy and money saving attributes, double glazed windows also offer the following benefits:

1. Noise reduction- If you live next to a main road, close to a pub or nightclub, near railway lines or an airport, or in an area with a lot of foot traffic such as in a city centre, you’ll certainly be aware of the negative effects noise pollution can have on your life. The lack of sleep that is often a result of living in a noisy area can contribute to all kinds of health related problems. With this in mind, limiting the amount of unwanted noise coming into your home should be high on your list of priorities, and a great way to achieve that is by choosing the right type of windows.

Of course, any double glazed windows will provide better protection to sounds than traditional windows but there are specific things you can opt for in order to increase the effectiveness of your windows.

Obviously the thicker the glass on your double glazed windows, the better the noise reduction, but also your choice of window frame, having a larger space between the two window panes, and having a laminated layer between them can all help to deflect and/or dissipate the incoming sound waves and leave you with a nice, relaxing, peaceful place to call home. There are also special types of glass that are designed to keep noise out but I’ll go into that later in this article.

2. Security- Unfortunately, we live in a society where break-ins and burglaries are all too common. Traditional single paned windows offer very little to deter any would be intruders. They are rarely fitted with any locks, never mind locks that would be considered secure by most people. Double glazed windows on the other hand can be fitted with wide variety of quality locks and multiple locking points.

Traditional window panes are often made of thin glass that is easily broken and contained within frame that allows the pane to be removed from the outside without too much effort by a skilled burglar. New double glazing glass is nearly always stronger than the older glass and having 2 panes that both need to be broken in order to enter the property, greatly increases the chances of any burglar being detected. The sound of two panes breaking in quick succession is a lot more likely to alert any one in earshot.

However, skilled burglars don’t usually break the glass, instead preferring to go the quieter route of removing the glass from the window. This is a fairly easy task on traditional windows where the simple removing of putty is all it takes.

Double glazed windows aren’t held in by putty and are much more difficult to remove so the chances of an intruder thinking twice before moving onto an easier target are greatly increased when you have good quality double glazed window units fitted in your home.

3. Durability– With a little maintenance, the longevity of double glazed windows far surpasses that of single paned windows. Your choice of frame will affect just how your long well maintained windows will last, as will the overall quality of the windows you buy (in general, more expensive windows last longer, cheaper brands will need replacing sooner) but you can expect your new windows units to last 10-30 years. Most double glazed windows come with a warranty of 5-20 years, so you’ll have an idea of what you can expect from your windows, durability wise, when you buy them.

4. Aesthetics– Swapping your old windows for new ones will almost certainly add aesthetic value to your home and can help with the resale of the property should that be in your plans. With such a selection of window types on offer, finding the right windows to improve the overall look of your home should be fairly straight forward.

In the next section of this page, we will look at the different types of double glazed windows available and hopefully guide you in the right direction towards making the right choices for your property.

Types of double glazed windows

Ok, it’s time to delve into the various types of windows available. The choices are:

Fixed windows

Fixed windows are windows that can’t be opened. Obviously, these aren‘t ideal for everyone but if you’re only looking to let more light in and ventilation isn’t a high priority (or you have other ventilation sources) for that particular room, fixed windows might be for you.

Sliding windows

Sliding Windows
Sliding Windows

Sliding windows open by sliding horizontally with the opened window sitting behind the closed one, much like a patio door thus providing less ventilation than some other types of window as one side has to be closed for the other to be open. They are often used in offices and schools because they’re easily opened and also have space saving qualities. If you have window on the side of your house that is too close to a garden wall or another property to have a window that opens outwards, horizontally sliding windows may be a sensible choice.

Casement windows

Casement Window
Casement Window

These are some of the most commonly seen double glazed windows. They allow good deal of light in and offer good ventilation. They are connected to the frame by hinges fixed on their sides and open outwards. Modern casement windows can also be locked in place once opened so there’s no fear of a sudden gust slamming your windows shut and potentially causing damage.

Sash windows

Sash Windows
Sash Windows

Sash windows are very common in older properties and have a great look to them. They open by sliding up and down and come in two variations- single and double hung. In single hung windows, only one pane can be moved while double hung windows allow both panes to slide. A common problem with traditional sash windows is that, over time, the sliding motion will start sticking, making the window hard to open. In other cases, the window can become very loose and the window can’t remain open without the aid of something propping it up.

With double glazed sash windows these things are not an issue. It is possible to have the traditional look but without the old problems plus the bonus of added security and longevity. On this site we have a whole page dedicated double glazed sash windows where you’ll find in depth information and also price charts. Please click here to view that page: sash windows

Awning Windows

Awning Window
Awning Window

Awning double glazed windows are a type of casement window that are hinged at the top. This means that they open outwards and upwards with special hinges that allow the window to stay open at angles without dropping back down. Because of the angle in which they swing, they can be left open for ventilation while still offering protection from rain that’s coming down vertically. Perfect for those stuffy, summer thundershowers.

Rotating or tilt and turn windows

Tilt and Turn Window
Tilt and Turn Window

Tilt and turn windows are very popular these days. Their special hinges allow for the window to be opened two different ways. Firstly, by pulling it which swings it open in the same way as casement windows albeit inwards rather than outwards, and secondly by tilting the pane backwards to a set angle. Switching between turning and tilting is as straightforward rotating the lockable window handle up or down. The design of tilt and turn double glazed windows makes cleaning the outer panes a much easier task than with other types of windows.

Bay windows

Bay Window

As you can see from the image, bay windows are usually comprised of 3 or more windows, angled so that they protrude the main outer wall of the property. They are most commonly used in modern houses on the front of the property as their beautiful design really catches the eye of anyone looking from outside. Inside the property, double glazed bay windows allow lots of natural light to flood in, really illuminating the room during the day. The size and angles of these particular double glazed windows give an expansive view of the outside and because bay windows protrude beyond the main outer wall, they can give a roomier feel to the inside of the home.

Double glazed window frames

Now that we’ve covered the different types of windows, it’s time to move on to another thing you’ll have to decide on when you purchase your own double glazed windows- what material you’d like your frames to be made of. The different materials you’ll get to choose from are uPVC, aluminium, and timber.

Here we’ll give you a little information about double glazed window frame options. If you’d like to read a more detailed article on the different types of frames, their pros and cons, price charts and comparisons, and more, please click on this link –cost of double glazing

The first window frame material we’re going to discuss is probably the most common- uPVC.

uPVC Windows
uPVC Windows

uPVC stands for unplasticized polyvinyl chloride. It is a lightweight yet strong plastic that offers good thermal efficiency, low maintenance and good security at very affordable prices. It’s a good all-round construction material that has kept customers happy for decades. It has a clean, modern look that is usually an improvement over older single pane window frames. uPVC may not be a great choice for all types of homes though. They might look a little out of place in older, more classical looking properties.

The second type of frame is aluminium.

Aluminium Window
Aluminium Window

When aluminium double glazed windows are chosen over their uPVC counterparts, it’s mostly for aesthetic reasons and increased longevity. uPVC window frames can sometimes seem a little bulky (especially the cheapest ones) and can hinder all the natural light from entering the house. Aluminium frames are sleeker in design and profile and offer a solution to the above problem. As already stated, high quality aluminium frames offer incredible durability as they don’t rust or degrade in the same way that uPVC frames do.

The last double glazed window frame material we will cover here is timber.

Timber Windows
Timber Windows

As the image shows, timber frames give your windows a really beautiful look. They are a great choice if your home has a more classic look or feel to it that you are hoping to retain. Timber double glazed windows are very thermally efficient, especially if paired with thick glass panes that have a wide space between them. There are two types of timber to choose from- hardwood and softwood. Hardwood is the more expensive of the two but also the most durable. Softwood is cheaper and therefore a good option for those who desire timber frames but have a tighter budget.

Types of glass

Just like with window types and frame materials, there’s a lot of choice when it comes to the types of glass you can have fitted in your double glazed window units. In this section we’ll examine the various options available and talk about their specific attributes. Let’s get started.

Low-E Glass- Low emissive or ‘low-E’ glass is designed to be very energy efficient. It has a special ultra-thin coating that reflects long wave infrared light and also ultraviolet light while not restricting visible light passing through. A low-E double glazed window works in much the same way as a thermos flask which has a lining that reflects temperatures, keeping the contents either hot or cold. Likewise, low-E windows reflect the heat back inside the house, keeping the temperature stable.

Low-E diagram
Low-E diagram

Actually, there are two different coatings available on low-E glass panes: Passive low-E coatings and solar control low-E coatings. Passive low-E coatings are designed to let heat in from the sun to reduce the need for other internal heating sources. Conversely Solar control low-E coatings restrict solar heat passing through and are designed to keep buildings cool.

Low-E double glazed windows are said to be able to reduce the amount of energy lost through your windows by up to 70%.

Acoustic Glass- For a lot of people, reducing the amount of noise that comes into their home from outside is very high on the list of factors when choosing their double glazing and this is where acoustic glass comes into play. Acoustic double glazed windows are usually made with a layer of PVB (Polyvinyl Butyral) between the two panes of glass that absorbs and weakens the sound waves as they pass through. This makes it ideal for use in office buildings where keeping the sounds of different departments separate or having a sound secure meeting room is important. Also, like we mentioned earlier, excessive noise pollution can adversely affect your health so if you’re living in a busy area, paying the extra for acoustic glass may be worth it.

Acoustic Glass Diagram
Acoustic Glass diagram

Safety Glass- Safety glass is a bit of a broad term as there are several different types of glass that could be referred to as that. Generally, safety glass is any glass that is more resistant to breaking or shattering into harmful pieces than regular glass. Here we will take a look at a couple of choices.

The first is laminated glass. This has the same design as acoustic glass with a layer of PVB between the two frames that varies in thickness. When the glass pane is broken, the shards and particles of glass stick to the layer of PVB and don’t fly out like normal glass windows, greatly reducing the risk of injury. Laminated glass is used in car windscreens for this and other reasons.

The second choice is toughened or tempered glass. This is glass that has been heated to very high temperatures then cooled quickly. This process increases the tensile strength of the glass by increasing the tension forces inside the glass. Tempered glass is roughly 5 times stronger than normal glass windows.

Either of these fitted into your choice of double glazed window frames would vastly increase the level of security of your home.

Fire glass- Fire glass has a lot of things to deal with: providing protection from fire, smoke and toxic fumes, resisting radiated heat, and more. It must also be resistant to breaking and not shatter in to shards if it does. That’s why the manufacturing processes of the types of fire glass are very similar to safety glass.

There is laminated fire glass which shares the same design as laminated acoustic and safety glass, with a layer of material fitted between the two panes of glass. Laminated fire glass can be filled with a gel that can absorb heat and works as a heat shield.

Then there’s fire glass that’s been thermally toughened like tempered fire glass. In addition to the strengthening, this type of glass can also have special coating that reflects heat and reduces radiated heat.

Self-Cleaning Glass- Yes, you read that right, double glazed windows that clean themselves. I know it sounds too good to be true, but they are actually a real thing. Here’s how it works: The glass is coated in a super-thin layer of titanium oxide. The way in titanium oxide cleans windows is twofold. Firstly, it’s a photo-catalyst which means that it can help to create chemical reactions when certain kinds of light are present. In this case, ultra violet light from the sun. This chemical reaction transforms the water molecules in the air into something called hydroxyl radicals that break down dirt from the surface of the glass.

But that’s not all, the hydroxyl radicals created by the titanium oxide layer have another trick up their sleeve. Usually, when rain hits a window with normal glass, it forms beads and then runs down the glass. With self-cleaning glass the rain forms into a thin layer or sheet of water which slides down the window uniformly, cleaning it like a large sponge.

Decorative Glass- As if having all of these options wasn’t enough, there is also decorative glass available in a multitude of colours, tints and patterns. It’s a great way to personalise your home and really make it stand out amongst the crowd. Take a look at these beautiful examples

Glass Combinations- Still can’t decide which type of glass you’d prefer in your double glazed windows? Let’s say you like the idea of Low-E glass for its energy saving properties but would also really like to stylise your home with decorative glass. Well, in this instance you really can have your cake and eat it. There are several double glazed windows available that are a combination of 2 or more of the types of glass mentioned above. If you’d like to know more, please contact our knowledgeable experts by either phone or email.

Double glazing existing windows

Some customers are interested in the benefits of double glazed windows such as better thermals, noise reduction and added security but they don’t want to completely replace their current windows. This could be due to the expense or maybe the difficulty involved in removing the existing window.

In these cases the customers have the option of having their current single pane windows transformed into double glazed windows. This is accomplished in two simple steps: First a sub-frame is installed on the inside of the existing windowsill. This is followed by an acrylic panel being fitted in, attached by magnets. An air tight seal is created by the magnets holding the window in place and forms an air cavity between the two panes like normal double glazed windows.

Generally, double glazing existing windows is cheaper than fully replacing them but there are a few things to keep in mind:

1. The existing windows have to be in good condition. There’s no point adding a new pane of glass to windows that are damaged or degraded through old age. All the benefits of double glazing we just talked about would be negated by the old windows. If you’re not a 100% sure about the quality and condition about your windows, you should have a professional inspect them before considering double glazing them. If they do indeed need repairing, the windows company that you are considering for your double glazing installation, may be able to repair them for you at the same time, making it more cost effective.

2. Make sure that the existing timber can support a double glazed window. If your property was built to house single pane windows, it might not be such a great idea to add the extra weight. In most cases it isn’t an issue, but you should still have this checked if you’re thinking of double glazing your old windows.

3. Draught proof your old windows before getting them double glazed. Old windows tend to be much more problematic with air leaks than modern ones, especially hung windows. The gains you get in thermal efficiency from double glazed windows wouldn’t really happen if the old window is too draughty.

So there you have it. Double glazing existing windows can save you money but only if you’re really confident that your current windows are up to the task. If not, the cost of repairs could end up with you spending as much, if not more, than on fully replacing them.

This concludes what we hope was a fairly comprehensive guide to double glazed windows. With so many options available, the thought of making the right decision may seem daunting. Which type of window would accentuate your property’s aesthetic value? Should you go with uPVC, aluminium, or timber frames? How do you know which glass would be best for your needs?

These questions and more may be swimming around your mind, and it’s perfectly natural. I would suggest getting a professional around to your home for an in depth chat and don’t be shy with the questions!

A good windows company representative should be able to listen to your wants and needs, inspect the property, tell you what your options are, and give you a quote. If you’d like to speak to one of our expertly trained staff, send us an email or give us a call and take your first step to getting the best advice, price and workmanship available for your double glazed windows.