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Guide to Double Glazed Units

Author: Jack Lloyd
Updated: Feb 01, 2024
6 minutes read
  • Double glazing reduces outside noise
  • Reduce energy costs with better insulation
  • Double glazed units last approximately 20 years

First becoming popular in the 1970s and 1980s, double glazed units only accounted for around 8% of windows across the UK. Nowadays, it is closer to 93%. There aren't many homes in the UK that have not upgraded to double glazing anymore, and for good reason.

All new homes are fitted with double glazing as standard now, including doors that have glass panes. A small percentage of older homes still feature single glazed units, but could benefit from upgrading to double glazed units to reduce costs and improve insulation and noise reduction.

Ready for double glazing? Use our quote comparison tool to find out how much you'd pay. It only takes a minute.

Double glazed windows from the outside of a home

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How Are Double Glazed Units Made?

Double glazing is relatively simple to make, which is part of its appeal. It is essentially two panes of glass, separated by a gap in the middle. This gap between the glass panes is then filled with air or inert gas, such as argon. The purpose of this is to help prevent condensation and to stop your units from becoming cloudy.

Air-filled double glazing is the cheaper option, but can be sensitive to rust. If you see condensation between the panes, your window is more likely to be an air-filled unit. Argon-filled double glazed units are the better option and will be more energy efficient and therefore reduce your costs each year. Their price tag may be slightly higher, but it pays off.

The graph below shows the uptake of double glazing in UK homes between 2008 and 2021. It has steadily been on the increase and the amount of homes with single glazing is dwindling. People are understanding the importance of double glazing and are making use of it to help with their heating costs.

Is Double Glazing Worth it?

Double glazing is absolutely worth it! Upgrading from single paned windows reduces energy consumption in your home and therefore lowers your carbon footprint, all while saving money long-term. There are a few more benefits to getting double glazed units installed; some of which are listed below. There are very few disadvantages to choosing double glazing, beyond the initial cost, which is dependent on your choices and the size of your property.

  • Able to increase your property value by up to 10%
  • Long lifespan and almost no maintenance requirements
  • Double glazing is harder to break into, increasing the security of your home
  • Interior fading can be reduced, with less heat from the sun making its way into your home
  • Reduce the risk of mould

How Much Double Glazing Costs

On the lower end of the scale, you could spend approximately £325 per uPVC window replacement and £250 for a uPVC door. The cost of double glazed units can vary depending on many factors. These include your choice of frame materials, locking mechanisms, the quality of the glass, whether the units are air-filled or gas-filled and labour costs.

To get 8 uPVC windows and 2 uPVC doors, you could spend £4,000-£5,000 on average. The cost will increase with additional double glazed units, especially if they are high up and require scaffolding to install them. They will also cost more depending on whether you choose uPVC, timber, aluminium or steel. You can find out more about the cost of double glazing here.

Also, you can apply for government grants for windows.

Best Material for Double Glazed Windows

There are four main materials used for the frames of double glazed units; timber, uPVC, steel and aluminium. Each have their own benefits and disadvantages. We have listed a few of these below, to help you decide which option is best for you.

Timber Frames

Timber is good for insulation but it is prone to warping and requires more maintenance and needs replacing sooner. Timber is still used for its aesthetic appeal for people who do not mind this additional cost.

Steel and Aluminium Frames

Both of these options offer the least when it comes to insulation. However, steel and aluminium frames are long lasting and can be recycled. They may be the best option for style and appeal, but not if you want to maximise on savings.

uPVC Frames

uPVC is the most popular choice of frame for double glazing frame material. It's useful in terms of energy ratings and insulation. They also tend to be the cheapest of all of the available options and they remain aesthetically pleasing. They are also practically maintenance free. This makes them one of the best choices, which is why so many are manufactured each year. Read our full guide on uPVC windows and doors.

How Do I Know When to Replace my Double Glazed Units?

Double glazed units can last approximately 20 years, making them a great investment. The older they get, the easier it will be to know when they need to be replaced.

Some people may opt for replacing just one window, rather than getting the whole house completely new windows but we do not recommend this as it will cost more in the long run. Some of the tell-tell signs that your double glazed windows need replacing are below.

Condensation appears between the glass panes

As your double glazed units start to deteriorate, you may start to see condensation appearing between the panes of glass. You may notice this more in the winter when you tend to have your heating on more. This tends to happen quicker with air-filled units.

You can hear more outside noise

This may not be as noticeable at first, but you will start to hear more noise from outside as your double glazed units start to age.

Your energy costs increase

Energy prices tend to increase each year but you may start to see a considerable increase in your energy costs as your double glazing start to need replacing. When you initially have your double glazed units installed, you can reduce energy loss by up to 54% but this will gradually decrease with each year.

They are stiff to open or close

Another sign that your double glazed units need replacing is that they are harder to open, close or lock. Extreme weather can affect the installation and make it swell or shrink, meaning they will not sit as snuggly as they once did.

The timber frame is rotting or soft

Unfortunately, if you opted for a timber frame, they require more maintenance and are sensitive to weather conditions. Whilst they often look nicer, they may not be the best option in areas that get a lot of rainfall. If you notice the wood on your double glazed units is becoming soft or chipping away, it is time to replace them.

Replace the Glazing or the Whole Unit?

Replacing just the glass panels in your double glazed units will be cheaper than completely replacing them, however, there is a good chance that they will not be as effective. This is because it is not just the glass panes that reduce noise and help to prevent heat loss, it is the frame too.

Completely new windows are designed and manufactured to fit seamlessly together. When you simply replace the glass panes, there is always the chance that they will not fit well in your existing double glazed units. This means that you will lose the benefits of your initial installation by spending less.

There are many companies that will replace the glass panes but most reputable companies will advise you to get completely new double glazed units installed, and this is not purely because they want you to spend more. It is because it does not work as well and you will ultimately spend more.

Things to Consider Before Installation

You will want to find the right company to install your new double glazing and it is important not to rush into a decision. We would recommend getting at least three bespoke quotes within your local area. This will ensure that travel expenses are not added to the final figure and the installation cost of your double glazed units should not differ too greatly. We have put together a handy guide for the best window installation company here.

Double glazing units come with efficiency ratings, much like fridges and other appliances. This is called a U-Value rating and their ratings range from A being the best and G being the worst. Make sure you check the rating value on your quotes.

It is also advisable to decide what you want to spend on your windows prior to getting a quote and ask for plenty of information before you sign on the dotted line. This will ensure that you get the best quality double glazed units for your budget range.


The benefits of double glazed units are clear. With the rapidly rising cost of energy, there is no better time to explore what is available to you. Get in touch to find out what you could be saving, whilst increasing your property value and improving the noise and insulation levels of your property.

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