Double Glazing Units & Windows: All You Need To Know

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Double Glazing Windows & Double Glazing Units

Learn about double glazing and the sealed units that make it work.

So you want to know a bit more about improving your home, making it more energy efficient, and maybe even a bit more comfortable, and you need a place to start – well, if you want to have a bit of cost-effectiveness and value for money in that mix, learning about Double Glazing Units and what they can do for your home is a good place to start.

Ready to go? Read on.

Here’s a quick overview of the essentials that we’ll cover:

Let’s get started!

A Little Bit of History

The history of double glazing.

Some say that double glazing units first appeared in Scotland during the Victorian era, though the exact date it was invented and who invented it remain uncertain. Double glazing units became common in the United States during the 1940’s and the 1950’s, though it wouldn’t be popular in the United Kingdom until the 1970’s came around.

In 1965, the United Kingdom passed its first set of national building standards, and subsequent refinements to these standards were passed as the years went by. These regulations would be critical to the improvements in building standards and energy efficiency that would follow in the years after. Builders were incentivized to invest in materials, methods, and technologies for building homes that would minimize energy wastage.

Prior to this point in time, however, most homes were built without much thought for energy efficiency. Fire remained the primary source of warmth, even in more prosperous households, as opposed to the central heating systems we have today. Homes were fitted with single glazing, which – while effective in protecting against the elements – caused problems with internal condensation, caused mould growth, which in turn caused potential health issues for residents.

The Benefits of Double Glazing Units

Double glazing benefits.

While it’s commonly acknowledged that double-glazed windows are a good idea in general, it remains useful to have in mind the benefits it provides:

  • Helps save on the energy bill. Double Glazing Units ensure that your home stays warmer in the winter, and cooler in the summer, all while requiring less power to maintain a comfortable temperature than it otherwise would without these. According to one source, DGUs prevent up to 70% heat loss and upwards of 75% heat gain.

  • Your home will be quieter. While it may vary with the type of unit installed and the materials used, having double glazing units installed ensures that you’ll be having less noise coming in from the outside, thanks to the vacuum or gas-filled interior space of the DGU, which prevents sound from passing through as easily as it would through ordinary windows or walls. Learn more about acoustic properties here.

  • Your Home Will Be More Secure. Due to how these are constructed, double glazed windows are tougher to break into.

  • Your Property’s Value Will Increase. Simply put, an energy-efficient home that saves its owners more money in the long run is an economic asset that makes it quite desirable compared to homes that are not.

What About Homes Without Double Glazing Units? Is It That Big of a Deal?

It’s certainly not an impossibility in terms of viability to live in a house without them, it’s just less comfortable and a bit costlier in the long run to do so. In what ways?

A lack of double glazing may result in poor heat retention.

For one thing, poor insulation means that it will be harder to retain heat inside your home and it will cost more to keep it warm during the winter months.

You also won’t have the added benefit of minimizing the amount of ambient noise coming from the outside, meaning that if you live in a fairly noisy neighbourhood, you won’t be able to enjoy as much peace and quiet – noise pollution can be costly in terms of the effect it has on your health, wellbeing, and productivity.

Finally, the property value aspect comes into play once more, for the reasons mentioned above: an energy-inefficient home simply isn’t as desirable as one that is.

Here’s one way to think about this: consider this an investment instead of an expense – as an investment, it will save you more in the long run, which you can look at as the returns that you’ll inevitably be getting, which – over time – can grow higher in value compared to what you may have initially invested.

For example, here’s how much the Energy Saving Trust calculates you’ll save every year on your energy bill if you installed double glazing units in your home:

£120 - £155 £80 - £110 £65 - £85 £55 - £75 £40 - £55

Let’s consider the fact that most quality double glazing units should last for a good 20 years, then let’s take the average of the potential savings across the board – if you save £100 every year for two decades, you can get a return of £2,000! Keep in mind, this doesn’t include the quantified cost of potential stress, loss of productivity, and health issues that you may experience every year due to the tangible, definable negative effects of energy inefficiency and noise pollution.

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Consider this an investment instead of an expense – as an investment, it will save you more in the long run, which you can look at as the returns that you’ll inevitably be getting.

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All things considered, not only is it a big deal, but you can say that it’s a pretty good deal.

Okay, What Should I Know About Double Glazing Units?

Not all double glazing units are created equal – some are better than others in terms of energy efficiency and durability, and these can depend on a few factors, such as materials used and Window Energy Rating (WER). Here are some of the more important details that you should keep an eye on:


There are several types of frame materials to choose from, each with their own characteristics


uPVC (unplasticized polyvinyl chloride)

Low maintenance, easy to clean (but gets dirty fairly quickly), durable, recyclable, available in a variety of finishes, most cost-effective option

This is the most common – and oftentimes the best – option that should work for most people


Good insulator, aesthetically pleasing, lower environmental impact, requires more maintenance and painting, may swell if not properly maintained, not the most durable, a bit more expensive

A suitable option for houses requiring this aesthetic, or if the home is listed (e.g., in a conservation area, etc.)


Slimmer, more compact, durable, lightweight, recyclable, available in a variety of colours, more expensive

More commonly used for commercial establishments and buildings with a modern aesthetic


Contains an inner timber frame covered with aluminium or plastic; low maintenance, weatherproof


In between the two panes of glass in a double glazing unit lies a space that is usually filled with non-toxic, clear, odourless, and low-thermal conductivity gas (or left in a vacuum) for the purpose of insulation. Here are some of the options that are available:

  1. Argon: Perhaps the most common and cost-effective, Argon retains heat 33% better than air.

  2. Krypton: The more uncommon and costlier option, Krypton retains heat up to 66% better than air.

  3. Vacuum Insulated Glass: Also known as evacuated glazing, VIG units are hermetically sealed, where heat loss through convection is eliminated.


Window Energy Ratings are assessments of how energy efficient a window is, on a scale of A to G, with A+ being the best, and G being the worst. According to Which?, the difference in the energy savings that you get between A, B, and C-rated windows isn’t that big, giving a difference of 6.5% additional savings if you go one rating higher, while the cost goes up 15% extra per window [9] – something you may want to bear in mind when making your selection.


Besides needing to know a little bit about the technical details, let’s not forget about the matter of aesthetics – what look are you going for? The Eco Experts have this to say:

There are many styles of double glazing [windows] to choose from. Some examples include sash windows, bay windows, and tilt & turn windows. The type of window best for your property will depend on the style of the property.

It is always best to match new windows closely to the ones you are replacing. It is also important to note the predominant style of window on your street in order to fit in with the neighbourhood aesthetic. Casement style double glazing windows are the most popular and the type that will usually be quoted as standard, if you do not specify otherwise.

The Eco Experts

Solid advice.

Things To Do Before You Buy

As with any investment of significance, it’s important to do a bit of research before pulling the trigger – here are some things you should consider doing:

  1. Get your requirements on paper. Having a good idea of the work you want or need to have done will help you get more accurate and specific quotes.

  2. Get quotes from more than one company. This will allow you to make direct comparisons and help you make an informed decision. Make sure the quotes you request are for the same products and materials.

  3. Find out about a company’s reputation by asking around. One way to get a good feel for a company is to know what their clients think about them, be it positive or negative. Additionally, you may want to see examples of a company’s work by asking the company directly, or perhaps see someone you know who has been a customer.

  4. Find out about a company or installer’s qualifications. It’s always a good idea to favour a double glazing installer registered with FENSA, BM Trada, or Certass. This ensures that their work complies with building regulations, and that there are additional protections for clients and mechanisms to resolve any issues that may arise.

  5. Consider paying by Credit Card if you can. This adds an extra layer of protection for you in case of any breaches of contract, among other possible issues that might pop up. You don’t necessarily have to pay for everything with the credit card; you may choose to use it to pay for just the deposit to begin with.

Should I Go with The Big, National Companies or Local, Independent Builders?

Once you’ve done your bit of research and you feel ready enough to go forward with your investment, you now have to decide who you want to transact with. One thing you may want to consider before making your decision is to ask and answer the question: “which of these companies have the most satisfied customers?”

According to research conducted by Which?, customers overall were 23% more satisfied and more likely to recommend independent and local double glazing companies compared to the big, national companies. Here’s a quick look at the summary of the report:

Independent 80-82%
Everest 59%
Anglian 56%
Safestyle 54%
Zenith 40%

To quote:

The vast majority of Which? members have used small independent companies rather than big brands, citing their local reputations as a main reason. One member said: ‘You cannot generalise for any type of company, but the small companies that have been in existence for many years tend to have a good reputation.’

As well as installation, quality of products and after-sales service, local companies and traders also tend to score higher for the manner of their sales staff and installers. 'Large companies deserve their poor reputation,' said another respondent, 'the whole process of inviting a salesperson into your house rapidly becomes a horrible experience of pushy behaviour, ridiculous initial quotes and silly "discounts".'

Of course, companies can change and things may improve, so there’s certainly nothing wrong with checking in to see if a good deal can’t be had with one or another of the above listed brands. That being said, it can also be much less of a risk to go with the safer choice of the company who tries harder to keep its customers happy.

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One thing you may want to consider before making your decision is to ask and answer the question: “which of these companies have the most satisfied customers?”

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What If I Have Problems with a Double Glazing Company?

In the event that you find something wrong with the work done by a builder, Which? notes: “The double glazing company has to make sure that any repair or replacement is carried out ‘within a reasonable time but without causing significant inconvenience’…”, as well as suggesting you take the following steps:

  1. Act quickly: as soon as you know there is a problem, contact the double glazing installer. If you phone, follow up the conversation with a letter. Confirm the problem and state what the double glazing installer agreed it would do and by when.

  2. Agree on a final date: if the double glazing installer doesn't sort out the problems when it said it would, contact the installer again. Agree on a final date by which the work must be completed.

  3. Final ultimatum: if the final deadline passes or the double glazing installer has done nothing to fix the problem, give the installer a final ultimatum. Say that if it doesn’t fix the problem within a short deadline, you will get someone else to do it and claim back the cost from the installer - by taking it to court if necessary.

  4. Evidence of problems: if the double glazing installer still doesn't respond or refuses to do the work, get quotes for fixing the problem from other glazing installers. But before they start work, make sure you have a report of the problems, including photographs where necessary. You will need this as evidence if you claim against the original double glazier in court.

  5. Court action: when the new double glazing installer has completed the work, write to the original double glazier claiming the money you have had to spend, and explaining exactly what work was done. If it does not pay up, you will have to start court proceedings to claim back the money. If the amount involved is less than the small claims limit (£10,000 in England and Wales and £3,000 in Scotland and Northern Ireland), you will be able to use the small claims court.

You can go to the Which? website to read more about your rights when buying double glazing.

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Customers overall were 23% more satisfied and more likely to recommend independent and local double glazing companies over the big, national companies – a satisfaction score of 82% versus 59%

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Some Parting Thoughts

At the end of the day, the decision remains to be made, and hopefully the information here helps you make an informed one at that. Due diligence done, double glazing company selected, and everything taken into consideration, you should – with a fair amount of confidence – find yourself in a comfortable position to really get the most out of your investment and make your house (or flat) an even better home, for a good many years to come.

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