What is double glazing?
Double glazing is a way of manufacturing windows to maximise their energy efficiency. Instead of a single pane of glass set in a frame, double-glazed windows consist of two panes, with a small gap - usually under 16mm - between them, sealed together to be airtight.[4]
That gap is created by a spacer bar around the edges of the window. The spacer bar is filled with desiccant, an absorbent material such as silica gel, which prevents condensation from building up between the panes.
That gap is filled with dehydrated air or an inert gas, such as argon, krypton, or xenon, that conducts heat more slowly than air. Newer double-glazed windows are made of low emissivity (low-E) glass, which is coated so it reflects infrared radiation, a component of heat, back into the home. This is similar to the way a thermos works and further reduces heat loss. The coating is transparent and allows light to pass through.
Double-glazed windows provide better insulation than single-pane windows, slowing the transfer of warm air outside in the winter and into your home in the summer.
Will double-glazed windows save me money on my energy bills?
By providing better insulation than single-glazed windows, double-glazed windows prevent the loss of heat so your boiler or other heating system doesn't need to burn as much fuel to keep your home at a comfortable temperature. That means lower energy bills.
In fact, it was the 1973 oil crisis which spurred Britons to adopt double-glazing. With fuel prices soaring and energy scarce, we started looking for ways to cut our fuel use and bills, including more heat-resistant windows. By the 1980s double-glazed windows had become standard in new homes in the UK.
How much exactly can you save by replacing single-glazed windows with double-glazing? The Energy Saving Trust estimates that installing A-rated double-glazed windows on a semi-detached, gas-heated home with entirely single-glazed windows could save you up to £140 per year on your energy bills. If you invest in even better A++-rated double-glazed windows, you could save up to £150 per year on the energy bills for the same property.[5]
The Glass and Glazing Federation (GGF) estimates the savings are even greater. It says upgrading home windows to “current standards" could save households up to £395 per year.[6]
Even if you already have double-glazed windows, replacing them with current models could save you energy. The GGF says that double-glazed windows installed before 2002 are 50% less energy efficient than current models.[6]
Your exact energy savings will vary depending on the size of your home, the number and size of its windows, and other insulation measures present. Double-glazed windows will make a bigger impact on a property with large windows or not much other insulation.
Double glazing vs triple glazing: What’s the difference?
Triple glazing goes one step further than double-glazing, adding a third pane of glass into the window, separated by a spacer bar and with the tiny gaps filled with inert gas.
Triple-glazing was first developed in the 1960s and 1970s in Scandinavian countries, where the winters are bitterly cold and governments have long pushed energy efficiency. But triple-glazing didn’t catch on in relatively balmy Britain until the 2010s when advances lowered the price of triple-paned windows and the government and consumers became more conscious of the carbon emissions of home heat.
Then, just as it did in the 1970s, an energy crisis pushed more homeowners to install state-of-the-art windows. Since the 2021-23 natural gas crisis, Britons have been looking for more ways to make their home heat go further, including triple-glazing. While the government doesn’t have any hard data on how many UK homes have triple-glazing, glass manufacturers and builders report it’s increasingly common, especially in new builds designed for efficiency and carbon neutrality.
How much better is triple glazing than simple double glazing? Double-glazed windows have a typical U-value, a measure of heat resistance, of 1.6, while triple-glazed windows achieve values of 0.8.[7] That means triple-glazed windows are 50% better at retaining heat than double-glazed windows.
While they’re 50% better, triple-glazed windows only cost 10-20% more than double-glazing, making them a great investment, especially for people interested in future-proofing their home or living in colder regions of the country.[8]
Styles of double-glazed windows
Double glazing is available in windows of every style to suit personal preferences and the architectural design of your home.
Popular window styles with double-glazed models available include:
Casement windows
The most popular style of double-glazed windows in the UK, casement windows are hinged on the side and open outwards. They may consist of a single pane of glass or multiple panes. A recent innovation is the flush casement window, which when closed sits flush within the frame. uPVC flush casement windows are the most energy-efficient on the market.
Sash windows
Sash windows are found in older homes, including Georgian, Victorian, and Edwardian properties, and consist of two panes of glass stacked on top of each other that slide vertically.
Georgian bar windows
Another popular choice for historic homes, Georgian bar windows are a type of sash window with up to six panes of glass, arranged in a grid. Most modern Georgian bar windows don’t actually have separate panes of glass but rather have astragal bars applied to the glazing on the inside and outside of the window to create the appearance of separate panes.
Tilt and turn windows
Tilt and turn windows have a dual-hinge system which allows them to open on two axes. They can tilt inward from the top or open outward like a casement window. They’re a popular choice for parents because they allow the window to be safely tilted at the top for ventilation with the handle child-locked.
Awning windows
Awning windows are a type of casement window hinged at the top and swing outwards, providing ventilation and blocking rain.
Bay and bow windows
Bay windows, extending outward from the main walls of the building, were a popular choice in many architectural periods, especially the Edwardian and Victorian eras. The windows in bays are set at angles and can easily be replaced with double-glazed casement, sash, or fixed windows. Bow windows are a smoothly curved variant of bay windows which can also be double-glazed. In the most elaborate bow windows, the glass itself is curved.
French windows
Also known as French doors, these windows open out on hinges, often leading to a garden or balcony.
Sliding doors
Consisting of large panes of glass that slide horizontally, sliding doors are popular in the rear of homes, providing access to a garden or patio.
Bi-fold doors
Bi-fold doors are another glass door option and are made of large panels of glass that fold up like a concertina. They maximise the door opening and can create a seamless transition between indoor and outdoor spaces.
Skylights
Skylights: Installed in the roof, these windows provide light and ventilation but also privacy. They’re often installed in bathrooms and lofts.
Fixed windows
Fixed windows: These windows don’t open and are ideal for places where you want light but don’t need ventilation. For instance, picture windows are large fixed windows without bars, usually paired with working casement or sash windows at the side.
Types of double-glazing materials
A variety of materials are used for the frame and glass of double-glazed windows, each with advantages and disadvantages.
For frames, the most common materials are uPVC, aluminium, and timber:
uPVC or unplasticized polyvinyl chloride, is a popular affordable option. uPVC is itself insulating, further reducing heat loss from the window. It’s also durable: weather-proofed so it’s suitable for all climates and resistant to corrosion and rot so it doesn’t need to be treated or re-painted. uPVC windows are available in a variety of styles and colours, including faux wood. However, some people don’t like the look of uPVC, and the material, while recyclable, is not biodegradable.
Timber is the traditional choice for window frames and provides a classic look that some homeowners prefer and may be required in conservation areas. Wood window frames are thermally resistant but less durable than uPVC, requiring regular repainting or treating otherwise they may rot or warp. Timber-framed windows are more expensive but are an environmentally friendly choice, especially when the wood is sourced from sustainably managed forests.
Aluminium window frames are stylish, with thin black frames offering a contemporary, minimalist look while supporting large frames of glass. They’re also robust: resistant to rust and corrosion, especially when powder coated, and low maintenance. However, aluminium conducts heat and cold, which can create thermal bridging, reducing the thermal resistance of the window and causing condensation. The best aluminium windows have a thermal break between the internal and external window frames.
Double-glazed windows also used different types of glass, varying in their manufacture, coating, and the contents of the tiny gap between the panes:
Float glass
Also known as annealed glass, float glass is the most popular and affordable glass used in double-glazed windows but has less thermal resistance than other glass types.
Low-emissivity (low-E) glass
Low-E glass has a transparent metallic coating that reflects infrared radiation while letting light pass through, increasing thermal resistance and limiting the amount of UV that enters a home to reduce fading of furniture and carpet. It’s more expensive but pays for itself by being better insulating.
Tempered glass
Also known as toughened glass, tempered glass is a safety glass that’s treated to be four times stronger than float glass.[9] When it does break, it breaks into small, blunted pieces. It’s a good choice for large windows or areas at risk of impact, such as sliding doors.
Laminated glass
Another type of safety glass, laminated or multi-layered glass consists of two sheets of glass bonded with a transparent interlayer. That plastic interlayer doesn’t break and keeps the glass intact even if it shatters. Laminated glass is also good for sound insulation and a popular choice for windows that face busy roads. It also blocks UV radiation into a home.
Gas-filled glass
The gaps in some double-glazed windows are filled with inert gases rather than dehydrated air. These gases are denser than air, offering more thermal resistance. The most common cheapest gas used is argon. Krypton is more expensive but offers more thermal resistance, especially in narrow gaps such as in triple-glazed windows and in double-glazed windows in older homes that were designed to accommodate only single-pane windows. The most advanced windows use xenon gas, which is even more expensive and typically reserved for glass walls and large panes in commercial buildings.
How much do double-glazed windows cost?
The cost of double-glazed windows varies, depending on the style and size of the window and the frame and glass materials used.
The cheapest option is a casement window with a uPVC frame and float glass, costing between £150 and £300 per window, before installation costs. Timber and aluminium frames increase costs, as do specialised glasses. The larger the window, the more expensive it’ll be.
Typical costs for standard-sized casement and sash windows follow:
Casement windows
Float glass | Low-e glass | Tempered glass | Gas-filled glass | |
|---|---|---|---|---|
uPVC frame | £150-£300/window | £250-£400/window | £250-£400/window | £300-£450/window |
Timber fram | £300-£600/window | £450-£750/window | £450-£750/window | £500-£800/window |
Aluminium frame | £250-£500/window | £350-600/window | £350/£600/window | £400-£700/window |
Sash windows
Float glass | Low-e glass | Tempered glass | Gas-filled glass | |
|---|---|---|---|---|
uPVC frame | £250-£500/window | £350-£600/window | £350-£600/window | £400-£650/window |
Timber fram | £400-800/window | £550-£1,000/window | £500-£1,000/window | £600-£1,100/window |
Aluminium frame | £350-£600/window | £450-800/window | £450/£800/window | £500-£900/window |
You’ll also need to pay for professional installation. For standard uPVC and timber windows, installers usually charge between £100-£250/window. For more complex installations, such as aluminium frame windows, sash windows, or large windows, you’ll pay £250-£400/window. Labour costs are higher in London and South East of England.
The typical 3-bedroom home has 8 to 12 windows.[10] Installing uPVC-framed float glass double-glazed windows in such a property could cost between £2,000 and £4,800, including labour.
If you have more complicated windows, choose timber or aluminium frames or specialist glass, the cost can easily exceed £10,000.
Are there any grants for double-glazed windows?
The government is committed to improving the energy efficiency of homes to meet the UK's decarbonisation targets and increase energy independence. Several grants and loans are available to fund home energy efficiency upgrades, including double-glazed windows and insulation.
The fourth edition of the Energy Company Obligation (ECO), running until March 2026, requires large energy suppliers to fund home upgrades for homeowners and private tenants who claim certain income-based benefits and live in properties with EPC ratings of D or worse. Those upgrades may include double glazing.[11]
In participating local authorities in England, the Home Upgrade Grant (HUG) funds free energy-saving improvements for low-income households in energy-inefficient properties. These improvements may include double glazing. Use the government’s website to check your eligibility.
In Scotland, the Home Energy Scotland programme offers some residents interest-free loans of up to £8,000, but importantly not grants, to replace single-glazed windows with double-glazing.[12]
If you don’t qualify for government grants or loans for double-glazed windows, you can explore financing options through big providers such as Anglian, Everest, Safestyle, and others.
Are double-glazed windows worth it?
If you live in one of the 12% of UK properties without double-glazing, better-insulated windows are one of the best investments you can make in your property. Even if you already have double-glazing, you may want to replace older windows with newer double-glazing with better technology and heat resistance.
Advantages of double-glazed windows include:
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Lower energy billsSave up to £150 per year by increasing the thermal efficiency of your home.
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More comfortable homeWith double glazing your home will feel warmer in the winter, including next to the windows, and cooler in the summer.
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Better acoustic insulationDouble-glazed windows can reduce external noise by up to 65%, or 35 decibels, compared to single-glazed windows.[13]
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Limit condensationBecause double-glazed windows keep the internal pane of glass at a higher temperature, condensation is less likely to form on the window, at least while the seal is intact. Condensation can cause mould and structurally damage the window.
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UV protectionMany double-glazed windows have coatings that filter out UV rays from the sun, which would otherwise fade furniture, carpets, and artwork over time.
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Improved home securityDouble-glazed windows are harder to break, creating an extra barrier for burglars. Newer models have advanced locking mechanisms.
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Increased property valueAccording to a 2023 Rightmove survey, double-glazing was the sixth most-in-demand feature for home-buyers and the first most-in-demand feature for renters, meaning you can charge more for the home.[14] Installing double-glazed windows on a home with single-pane glass can also push the home’s EPC numerical score by up to 10 points, improving its letter rating, and thus its value.[15] The Mortgage Advice Bureau estimates that a move from an EPC rating of D to C can increase a home’s value by 3%, for example.[16]
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Smaller carbon footprintBy reducing the energy needed for heat, double glazing can reduce a home’s carbon emissions by up to 680kg annually.[17]
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Some types are low maintenanceuPVC and aluminium double-glazed windows require little maintenance and are weather-proofed, so not vulnerable to rot and corrosion.
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Longevity
Disadvantages of double-glazed windows include:
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High upfront costYou can expect to pay between £2,000 and £10,000+ to install double-glazing on all windows in your home.
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Professional installation requiredInstalling double-glazing isn’t a DIY project and professional installation costs at least £100 per window.
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Seal failure can cause condensation within the windowThe seal between the panes can deteriorate over time, letting moisture between the sheets of glass. This gives windows a cloudy appearance and compromises their thermal resistance. Once the seal has degraded, the entire window unit needs to be replaced.
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Difficult repairsDouble-glazed windows are tricky to repair and damage often means the entire window unit needs to be replaced.
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Aesthetic considerationsAlthough double-glazed windows are available in a variety of styles, they may alter the appearance of a property.
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May not be permitted in conservation areasIn conservation areas, double-glazing may be banned or require special permission in order to maintain the historic character of the homes.
What are the best double-glazed windows?
Double-glazed windows are a big investment so you want to be sure you’re getting the best model: the most thermally resistant, the most durable, the best fit for your home’s aesthetic look.
Like appliances, every model of double-glazed windows is rated on its energy efficiency, from E (the worst) to A++ (the best). These Window Energy Ratings (WERs) are set by the British Fenestration Rating Council (BFRC) and are the most straightforward way to assess a window’s performance. Under current building regulations, new buildings must have windows that rate at least at B.[19]
You can also get into the weeds and consider each model’s U-value, a measure of its heat resistance. The lower the U-value, the more energy-efficient a window is. The U-value of a typical double-glazed window is 1.4. A++-rated windows will have U-values as low as 0.8.[20]
Window manufacturer | Styles of windows produced include | Frame materials | Ratings up to | Guarantee |
|---|---|---|---|---|
Anglian | Casement, sash, bay, cottage, tilt and turn, French doors, bi-fold doors | uPVC, wood, aluminium | A as standard for double-glazed windows (A++ for triple-glazed flush casement windows) | 10 years |
Everest | Casement, sash, tilt and turn, French doors, bi-fold doors | uPVC, wood, aluminium | A+ for doubling glazing (A++ for triple glazing) | 10-20 years |
Safestyle | Casement, sash, tilt and turn, bay windows, French doors, bi-fold doors | uPVC | A for all uPVC casement windows (A++ for triple glazed uPVC flush casement windows) | 10-15 years |
FAQs
How long does double glazing last?
You can expect double-glazed windows to last at least 25 to 30 years, a decade longer than single-pane windows. Major manufacturers offer warranties on their double-glazed windows for between 10 and 20 years.
With proper care and in certain climates you may be able to extend the lifespan of double-glazed windows to up to 50 years.
Factors that affect the durability and lifespan of double-glazed windows include:
Material: uPVC and aluminium windows usually last longer than wood windows, which must be treated and painted at regular intervals
Proper installation: Double-glazed windows must be sealed to the elements. Improper installation allows water to enter the windows, causing condensation and damage.
Location of the windows: Windows that directly face the sun expand and contract as the temperature changes, stressing the window's seal and eventually causing it to fail. Windows sheltered from sun, wind, and rain by awnings or trees will last longer.
Local conditions: In coastal areas, saltwater and wind will increase wear and tear on the windows. Windows also have shorter lifespans in very rainy regions.
How can I check the efficiency of double-glazed windows?
All windows sold in the UK have been assigned a Window Energy Rating (WER) by the British Fenestration Rating Council as a measure of their energy efficiency. The best double-glazed windows can achieve a top score of A++, while single-pane windows may be rated as low as E. These ratings along with a traffic light colour system should be included in the marketing of the window.
Already have double glazing and wondering if it’s holding up? Look for signs that it’s losing heat by feeling around the window’s edges for cold air or checking the temperature of the glass with an infrared thermometer. Cold internal glass means the double-glazed window isn’t working as well as it should.
Does double glazing reduce noise?
Yes, double glazing will reduce the amount of outside noise that enters your home and indoor noise that can be heard outside. The two panes of glass reflect sound waves, while the gas inside absorbs some sound waves.
Double-glazed windows can dampen outside noise by up to 65% or 31 decibels, which will certainly reduce irritation from the road and your neighbours' barbecues. However, double-glazing itself isn’t soundproofing. Glass doesn’t absorb noise and achieves its noise-dampening effects by reflecting it.
To block out more noise, you need acoustic glass, which is laminated with polyvinyl butyral (PVB) to absorb noise. Acoustic windows are usually double-glazed, using two panes of this laminated glass.
Resources:
- https://www.gov.uk/government/statistics/chapters-for-english-housing-survey-2022-to-2023-headline-report/chapter-5-energy-efficiency
- https://www.planningportal.co.uk/permission/common-projects/doors-and-windows/building-regulations
- https://www.lsllandandnewhomes.co.uk/blog/new-build-homes-the-key-to-lower-energy-bills
- https://www.prenton-glass.co.uk/how-much-you-can-save-with-energy-efficient-windows/
- https://energysavingtrust.org.uk/advice/windows-and-doors/
- https://www.ggf.org.uk/window-of-opportunity/
- https://www.homebuilding.co.uk/advice/which-wall-material-has-the-best-u-value
- https://www.fmb.org.uk/homepicks/windows/triple-glazed-windows/
- https://dakea.co.uk/articles/windows/what-are-tempered-glass-windows/
- https://www.fmb.org.uk/homepicks/windows/cost-to-double-glaze-three-bed-house/
- https://www.ofgem.gov.uk/environmental-and-social-schemes/energy-company-obligation-eco
- https://www.homeenergyscotland.org/home-energy-scotland-grant-loan
- https://phairwindowsandglass.co.uk/can-double-glazing-reduce-outside-noise/
- https://www.rightmove.co.uk/news/articles/property-news/10-most-in-demand-features-buyers-renters/
- https://www.belvoir.co.uk/articles/epc-rating-101/
- https://www.mortgageadvicebureau.com/green-hub/how-your-epc-rating-impacts-your-property-value/
- https://www.leeglass.com/news/double-glazing-save-money-heating-bill/
- https://www.checkatrade.com/blog/expert-advice/window-replacement/
- https://assets.publishing.service.gov.uk/media/662a2e3e55e1582b6ca7e592/Approved_Document_L__Conservation_of_fuel_and_power__Volume_1_Dwellings__2021_edition_incorporating_2023_amendments.pdf
- https://www.norrsken.co.uk/newsitem/U-Values
Author
Fergus Cole is a writer with nearly a decade of experience producing informative, evidence-based articles that help the public better understand important issues and current affairs. After studying at Leeds University, he went on to lead a successful digital content management team that has published thousands of guides, essays, and news articles across industries ranging from broadband technology and mortgage advice to sustainable travel and renewable energy. He has a particular passion for creating accessible, timely pieces on policy changes, helping readers navigate financial challenges during uncertain times.
Activity History - Last updated: 26 November 2025, Published date: 04 November 2025
Reviewer
Energy Expert
Mike is a recognised leader in the UK energy sector with over two decades of experience, having run one of the country's most trusted Ofgem-accredited energy comparison platforms before selling in 2019. Today, he advises EnergyComparison.co.uk and works with businesses on the transition to net zero.
Activity History - Expert Reviewed on 05 November 2025 and last checked on 26 November 2025