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We take a look at how double glazing windows work and whether they are the best option for energy efficiency in your home.
Our comprehensive guide explains everything about double glazed windows and their installation, from frame materials, styles, and windows prices, to the installation process and consumer rights.
They help to keep warm air inside during the winter and hot air outside during the summer and their insulation reduces energy costs by minimising the need for central heating to maintain comfortable indoor temperatures. Additionally, double glazed windows can reduce noise pollution from the outside and increase a property’s security and value.
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The manufacturing process for double glazed windows is quite straightforward; each unit is created by cutting two panes of glass according to set measurements. Then, the spacer bars are manufactured to size by double glazing companies to ensure that they separate the two panes to reduce heat transfer and improve thermal insulation. This space is often filled with air or inert gases, which are poor conductors of heat.
These spacer bars are made using materials with a low thermal conduction rate, which reduces heat loss. One pane of glass is fitted with the spacer bar in position before being moved through an argon-filled chamber. The second pane is pressed on top to seal the unit and trap the argon gas, creating a vacuum.
Argon gas is used for double glazing because it is more dense, slow-moving and less conductive. This significantly reduces conduction through the gas because the density is greater than that of air.
Once the frame is filled with argon gas, the unit is sealed around the edges to make the space airtight. This ensures that the gas can neither escape nor air enter, and maintains the frame’s structural integrity. Once complete, the units are ready for assembly using the chosen frame material.
Double glazed windows originated in Victorian Scotland to combat cold, windy winters. In the 1930s, they were commercially patented in the US by CD Haven as Thermopane and, due to their high prices, were associated with luxury, sophistication and superiority.
By the 1960s, the UK began producing them for better insulation, addressing the shortcomings of single-pane windows, such as increased condensation. Legislation from 1965 onwards aimed to regulate the industry and promote energy efficient materials, including double glazing. By the 1990s, 60% of UK homes had adopted double glazing, significantly improving home comfort. Companies like Everest advanced the technology, introducing aluminium and uPVC double glazing units in the late 20th century.
Many homeowners are installing replacement windows to help reduce their heating bills as the cost of living crisis is still impacting household budgets. Besides lowering bills, double glazing offers several other benefits.
Double glazing keeps your home warmer longer by reducing heat loss through windows by about 18%, potentially saving up to £235 annually. This improvement is due to its insulating properties and reduced need for heating.
Double glazed windows are tougher and harder to break than single-pane windows. They generally include multi-point locks and are designed to resist being forced open from the outside. Options like toughened or laminated glass are available for enhanced security.
Double glazing’s sound-insulating properties significantly reduce noise intrusion from busy roads, flight paths, or noisy neighbours.
Installing double glazed windows can enhance your home’s aesthetic and increase its market value by up to 10%.
Double glazing reduces energy consumption and reliance on fossil fuels, potentially lowering your carbon footprint by up to 410kg annually. The most commonly used material, uPVC, is recyclable and sustainable, contributing less waste to landfills.
Double glazing helps prevent condensation and associated problems like dampness, musty odours, and mildew by keeping internal panes at room temperature and away from the cold outside air.
By blocking damaging UV rays, double glazing protects furnishings and wood from fading and cracking caused by sunlight.
Because double glazing is a sealed unit with a layer of gas between the two panes of glass, repairs are not as straightforward as single glazing. If the seal is broken and warm air is allowed to get between the panes of glass, the whole glass unit will have to be replaced, regardless if only one pane is broken. Blown double glazing repair can be costly. It is possible, however, to adjust uPVC windows, ensuring maximum efficiency is retained.
Double glazing windows can suffer from solar gain, whereby heat from sunlight becomes trapped inside your house. This can be useful in the winter because using sunlight to warm your home can reduce your reliance on central heating, but it may lead to an uncomfortable house during the summer.Choosing low-E (low-emissivity) glass can resolve this issue. It features a microscopically thin, transparent coating that reflects thermal radiation or heat. This coating allows light to enter while preventing heat from escaping or entering, improving a window’s insulation properties. It helps keep interiors warmer in winter and cooler in summer, enhancing energy efficiency.
While many companies have gone to great lengths to design double glazing windows that match traditional styles for older homes, there are restrictions on what kind of windows you can install in listed buildings, which may require planning permission to overcome. However, you can still improve your home’s energy efficiency by installing secondary double glazing, which is a pane of glass or plastic installed on the inside of a window that does not affect the outside appearance and doesn’t require planning permission.
Double glazing costs vary significantly based on materials, window type, and style. Your choice of installer can also impact the price, as some companies charge more than others for labour and materials.
Although this might seem a significant investment, with potential savings of up to £235 per year and more if prices continue to rise, the breakeven point is nearer than ever.
| Number of uPVC casement windows | Approximate prices |
|---|---|
| 1 – 2 | £500 – £1,300 |
| 3 – 5 | £1,500 – £3,250 |
| 6 – 10 | £3,000 – £6,500 |
According to Energy Savings Trust, installing A-rated replacement windows in an entirely single-glazed semi-detached property could save you £140 a year. If you replace single glazing windows with A++ rated double glazed options, you could save up to £235 annually.
There are several double glazing grants and loans available depending on your eligibility. The following schemes aim to reduce the costs of installing windows.
The Energy Company Obligation, or the ECO4, is a scheme where energy suppliers who have signed up provide funding for energy-efficient upgrades.
People who are part of the core group under the Warm Home Discount Scheme are eligible to apply or who receive at least one of the following benefits:
LA Flex is an extension of ECO4, offering financial support to those not meeting the ECO4 criteria. Your local authority has funding available to assist families on lower incomes with the cost of installing energy-efficient home improvements, including double glazing windows.
The British Fenestration Rating Council (BFRC) independently verifies a window’s thermal efficiency. This organisation developed a specific rating system similar to the one used on domestic appliance energy labels found on washing machines, freezers and fridges.
According to the BFRC, double glazing windows are rated between A++, providing the highest level of energy efficiency, and E, the lowest. UK building regulations require that all new windows be at least C-rated. Most double glazing companies have developed units with different levels of energy efficiency, some as high as A++, allowing you to choose the best option for your home and your wallet.
When buying double glazing, do ensure that BFRC has verified its rating.
Additionally, you’ll see the U-Value mentioned when looking for these energy ratings. This is a measure of how easily heat can pass through a material. Therefore, a higher U-Value means the amount of heat passing through is low. Some windows could have a low U-Value but a high energy rating because the energy rating looks at additional factors, such as how well the materials insulate and the type of gas or glass.
While double glazing offers significant insulation and energy efficiency benefits, it’s not the only option available to homeowners looking to enhance their property’s thermal performance. For those considering an investment in window upgrades, exploring all options can ensure you choose the most cost effective, suitable solution.
Triple glazed windows are becoming a popular option for homeowners and consist of three panes of glass separated by spaces filled with air or an effective insulator gas, such as argon. Set in a sealed unit, the properties held by double glazing are generally improved with three panes. With two spaces, or airlocks, the energy efficiency is increased by as much as 50%; however, triple glazed windows are around 20% more expensive than double.
Secondary glazing involves adding a movable second layer of glass or plastic to the frame of existing single glazed units. Installed on the window’s interior, it’s fully independent and doesn’t form a sealed unit like double glazed windows. Secondary glazing, although cheaper, is generally not as effective at keeping your home warm. It also doesn’t prevent condensation from building up nor add to your property’s security.
There are four types of window frames that you’ll most likely choose between during your double glazing windows installation process – uPVC, aluminium, composite and timber windows; but what are they, and what are the pros and cons of each?
The below table examines their advantages and disadvantages and should help you pick the right one for your home.
| Frame material | Pros | Cons |
|---|---|---|
| uPVC | Low maintenance, energy efficient, affordable price and secure | Can stain easily if not maintained |
| Aluminium | Frames are slim and sleek allowing for a larger glazed area and windows appear bigger | Frames are not as energy efficient as other materials |
| Wood | Wood frames are aesthetically pleasing and have the longest lifespan if they’re maintained properly | Wood frames are the most expensive and are high maintenance |
| Composite | Combines the look of a wood window inside, but appears aluminium on the outside – looks stylish and is durable, but with less maintenance | More expensive than uPVC window frames |
Gone are the days of plain casement double glazing units, and today many styles are readily available, meaning you can match the architectural exterior of your property, enhancing its appearance.
Casement windows are the most popular type. They suit most UK properties and are designed to allow as much light as possible. The windows can be opened with hinges on either side or the top, opening inwards or out – the choice is yours.
Tilt and turn windows are usually incorporated into casement window units. The units have a dual-hinge system, allowing them to be opened by tilting inwards from the top of the more traditional side hinge. This makes them ideal if you have young children, as the tilt action prevents anyone from climbing out and having an accident.
Sash, or vertical sliding, windows are ideally suited to a period property or in Victorian and Georgian architecture. Modern mechanisms, such as easy-slide balances and tilt-in designs, facilitate smoother operation and easier cleaning. These windows maintain the characteristic appearance of classic sash windows, including the vertical or horizontal sliding panels, but with updated energy efficiency, security features, and low maintenance requirements.
When considering double glazing for your home, several types of glass options are available, each designed to meet different needs. Here’s a breakdown of the various choices of double glazing glass:
Double glazing minimises heat loss thanks to the gas insulation in the sealed unit and the two glass panels. When the cold air from outside hits the external glass, it transfers the temperature to the argon gas layer. Since argon gas has a low conductivity rate, it slows the conduction between the outside and inside.
At the same time, when the warm air from inside the room hits the internal glass pane, the gas reduces the transmission of heat to the outside. While the exterior and interior glass panes will have varying temperatures, heat is retained in the room.
Double glazing windows provide a number of benefits. (Image credit: Adobe)
In the past 20 years, significant advances in double glazing technology have resulted in longer-lasting and higher-performing windows. Key improvements include:
These are the steps your double glazing installer will take when putting in your new windows.
How long it takes to install your new double glazing will depend on how many windows you have installed. For the majority of homes, installation can be completed within one day. Installation costs vary between companies but will average around £80 per frame.
The below table should give you an estimate of how long the installation process will take and the total costs.
| Number of uPVC casement windows | Costs (excluding installation) | Approximate installation time |
|---|---|---|
| 4–5 | £2,000–£3,250 | 1 day |
| 6–10 | £3,000–£6,500 | 2 days |
| 10+ | £6,500+ | 2 days+ |
Home improvements usually go off without a hitch, but there are horror stories of double glazing windows installations going wrong – incomplete work, incorrect installations, wrong-sized windows and even damage to people’s properties. If something goes wrong with your project, it’s essential to understand your rights as a consumer.
The most important step you can take is researching before contacting companies to gather quotes or signing any contracts.
Once you’ve chosen the quote that best matches your budget and vision of how your new windows will look, below are the things to remember as your installation progresses.
Be sure to read your contract carefully before signing it to understand what work will be undertaken and what terms the company has placed on the project. In general, your contract should include the following details:
General consumer rights state most sales contracts should include a cooling-off period of at least 14 days. This applies to agreements made online, over the phone or in person at your home, allowing the purchaser to cancel the sale risk-free.
However, if your windows are made specifically for your property or you signed the agreement at the installer’s premises, you will lose the right to cancel. This also applies if you discuss the sale with an advisor at your home and agree to it later, as you are then deemed to have had time to cool off and consider the contract.
If you discover a problem with your double glazing windows after your installation or something wrong with the work itself, you should be covered by your FENSA-backed guarantee, which is a requirement for installers to provide. You should contact the company in the first instance to resolve any issues.
You are also covered by the Consumer Rights Act 2015, which protects consumers from flawed products or services. The guidelines state any services should:
If you feel these criteria haven’t been met, your installer is required to put things right. However, it is up to the company to decide whether to repair them or provide replacements, and they will generally choose the cheaper of the two options.
FENSA also provides a complaints process if you cannot resolve directly with your installer, so long as they are a member.
Yes. The Double Glazing and Conservatory Quality Assurance Ombudsman Scheme offers a free consumer advice line and free access to its services, while The Glazing Arbitration Scheme (TGAS – formally the Glazing Ombudsman Scheme) can take cases to arbitration, which aims to resolve disputes without going to court; however, this scheme is only available if your installer is a FENSA or Glass and Glazing Federation (GGF) member and you have already been through their complaints process. Be aware that TGAS’s decision is legally binding, meaning you won’t be able to proceed to court action if you’re unhappy with the outcome of arbitration.
If you paid for part or all of your windows with a credit card or the windows company arranged finance on your behalf, and the sale was between £100 and £30,000, you will be covered by the Consumer Credit Act 1974, which makes your credit card provider equally as responsible as the installer for any disputes. This means you can claim up to the value of the entire sale. However, if you took out a bank loan to pay for the work, this does not apply.
Your last resort for resolving disputes with your installer is taking them to court to obtain an order for them to compensate you. Which court you turn to depends on the amount you claim – if it’s £10,000 or less in England and Wales or up to £3,000 in Northern Ireland, you can use the small claims court. In Scotland, you can turn to the Simple Procedure for claims of up to £5,000.
Be aware that court action can be costly and may take a long time to reach a decision.
Keep records of every step of your complaints process, including emails, phone logs, and other written communication with your installer, as well as pictures of any damage or faulty installation, as these can all be used as evidence to support your case.
Replacing double glazed windows is worth considering if they are old, damaged, or inefficient. New technological advancements offer improved thermal insulation, noise reduction, and security features. Upgrading can significantly enhance energy efficiency, lower heating and cooling costs, and increase property value.
Additionally, new double glazed windows can resolve issues like condensation between panes or drafts, improving the comfort and aesthetics of your home.
The cheapest way to replace double glazing involves opting for standard, off-the-shelf sizes and avoiding custom shapes or sizes. Choose a simple, less expensive frame material like uPVC over premium options like wood or aluminium. Consider secondary glazing a more affordable alternative to full replacement, especially if the frames are still in good condition.
Comparing quotes from multiple suppliers and installers can also help find the best deal. Undertaking installations during off-peak seasons might attract discounts. Lastly, consider only replacing the most inefficient windows first to spread costs over time.
No, it should not. If your double glazing has condensation on the inside between the glass panes, it’s not functioning as it should. This also means that the sealant is not doing its job and is allowing warm air to enter the gap between the two panes of glass. You should contact your installer to carry out a blown double glazing repair.
Double glazing reduces noise by using two panes of glass, separated by a gap filled with air or inert gas, to create a barrier that sound waves must penetrate. This structure significantly dampens external noise as the sound waves lose energy when passing through the different layers and the insulating gap. The thicker the glass and the wider the gap, the more effective the noise reduction. Additionally, special laminated acoustic glass can further enhance the soundproofing qualities of double glazed windows.
Typically, double glazing windows have a lifespan of 20 years minimum, but they can last as long as 50 years. Their longevity depends on several factors, including the quality of the manufacture, the construction material, and how well they’ve been maintained.
