How do double glazing windows work?

How do double glazing windows work? And what are the benefits? We look at the science and answer some of your frequently asked questions.

By Architectural Digest UK Reviews Team

October 19, 2023
A cross section showing how double glazing windows work with two panes of glass separated by a spacer bar.

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Jump to: What is double glazing? | How do double glazing windows work? | Benefits | Window ratings explained | Types of glass | How much can you save? | FAQ

Double glazing has been an established trend with homeowners for some time now, but how do double glazing windows work? In this article, we dive into the world of double-glazed windows, exploring their benefits, how they keep our homes warmer and more energy efficient, and the different types available. We’ll also answer some of the most frequently asked questions about double glazing.

What is double glazing?

A cross section showing how double glazing windows work with two panes of glass separated by a spacer bar.

 (Image credit: Adobe)

Double glazing is a window with two panes of glass separated by a layer of insulating gas. 

The gas layer in between the glass panes provides many benefits, such as noise reduction, reduced condensation, and reduced heat transfer, which means better energy efficiency and lower energy bills.

How do double glazing windows work?

A double glazing window consists of the following:

  • Double-glazed unit or insulated glass unit (IGU)
  • Air space
  • Spacer
  • Timber, aluminium, or uPVC frame
  • Desiccant
  • Seal

Double glazing windows work by creating an insulating gas layer, typically of air, xenon, argon, or krypton, between two panes of glass. This reduces heat transfer between the different temperature zones inside and outside your home.

Each glass pane for a double-glazed window usually has a thickness of 4 mm to 6 mm with a gas layer in between measuring 6 mm to 20 mm in thickness. The total average thickness of the unit is 24 mm. If your goal is to minimise heat loss and maximise noise reduction, we recommend using a thicker double-glazed or even triple-glazed unit. However, these do come at a higher cost.

What are the benefits of double glazing windows?

Double glazing windows work to improve your home in a number of ways in addition to their insulating properties.

Increased security

With double glazing windows, you can rest easy knowing they are much harder to break compared to windows with a single glass pane. The seal around double-glazed windows also makes them harder to break.

If you’re looking for more security, then you might consider using laminated or toughened glass for your double-glazed windows.

Reduced energy bills and higher thermal insulation

Double-glazed windows were designed to provide better thermal insulation over single-glazed windows. The double glazing acts as a barrier for heat transfer, which means you will benefit from warmer winters and cooler summers. This translates into needing to use your air conditioning and central heating less, which can save you money in the long run.

Reduced condensation

If you’ve noticed water droplets forming on your windows, this could be due to condensation. This occurs when your windows are cooler than the temperature inside your house, and it can cause mould and mildew to grow. Furthermore, the humidity can rot your wooden frames, impacting both your health and wallet.

Double glazing windows reduce condensation because the temperature of the inner glass pane is closer to the temperature inside your house.

Noise reduction

Double glazing has a greater effect on noise reduction when compared to single-pane windows because of the additional pane of glass and the internal gas layer. Depending on the configuration, double glazing can reduce noise transmission by 19% to 57% when compared to single-pane windows.

So, if you live in a noisy area, double glazing windows will make your home quieter. This could be particularly useful if you live near a busy road, for example.

Higher property value

Installing double-glazed windows makes your home more energy-efficient, comfortable, and attractive to potential buyers. According to research, sellers can sell their property for up to 10% more when it has double glazing.

Reduced interior damage

If the furniture closer to your windows is getting discoloured or damaged, this is likely being caused by ultraviolet (UV) rays. Double glazing windows limit the sun’s UV rays entering your home and can save you money on replacing damaged furniture.

If you want to further limit UV rays entering your house, we suggest adding a UV coating to your double-glazed windows. This is a thin film that’s applied to the glass and can either be purchased as an add-on with your double-glazed windows or separately from companies like 3M.

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Double glazing window ratings explained

A chart of the energy efficiency ratings given to double glazing windows by the British Fenestration Rating Council (BFRC).
The BFRC gives all windows an energy efficiency rating between E, the least efficient, and A++, the most efficient. (Image credit: BFRC)

We recommend looking at the energy rating and U value when selecting double glazing windows.

Energy rating

The energy rating system for double glazing was developed by the British Fenestration Rating Council (BFRC) and judges the energy efficiency of each window component, from the casement to the frame.

Double glazing windows are checked to see how well they reduce heat loss and air leakage. They’re also assessed for their solar gain—the light and heat from the sun that enters through the window and contributes to keeping your home well lit and warm. The rating will verify how much light passes through without harmful ultraviolet (UV) rays.

After being checked by regulators and professionals, the double-glazed windows are given a window energy rating (WER). Windows are graded from A++ (highest efficiency) to E (lowest efficiency).

This rating can help consumers select the right double-glazed windows for their budget. By law, all new double glazing windows installed in the UK must have an energy rating of C or above.

The U value

The U value is the measure of how well a building object transmits heat. The lower the U value, the better the windows are at reducing heat transmission between the outside and inside.

A typical single-glazed window has a U value of 5.88, while the standard double glazing window has a U value of 2.81, meaning the latter can reduce heat transmission by approximately 50%. This can be further increased by using different glazing standards.

What are the types of glass used in double glazing windows?

When selecting windows, there are many factors to consider, such as glass type, frame type, style, and size. The most important of these factors is the glass type, as it has an impact on how double glazing windows work.

There is a wide range of types of glass that can be used for double-glazed windows, from strengthened glass to self-cleaning glass.

Annealed or float glass

This is the most common type and offers the most cost-effective solution for double glazing. Float glass goes through a process of heating and gradual cooling to make it more durable.

However, float glass is considered to be softer in comparison to other types of glass.

Float glass is ideal for:

  • Low-cost double glazing units
  • Locations where window breakage is unlikely
  • Locations where health and safety concerns are minimal

Tempered or toughened glass

Tempered glass has been chemically or thermally treated to make it more durable and safer. It is four times more durable than float glass and is the recommended choice where safety is a priority.

Tempered glass is ideal for:

  • Locations where there are extreme weather conditions
  • Locations with high crime rates
  • Zones with high traffic volumes
  • Longer-lasting and cost-effective double glazing solutions

Laminated glass

This consists of two or more layers of glass joined by a plastic resin layer, typically polyvinyl butyral (PVB). If broken, the PVB layer holds the glass shards together, preventing injury. Laminated glass has the added advantage of reducing noise.

Laminated glass is ideal for:

  • High-security locations
  • Roof windows and skylights
  • Locations where the risk of glass breakage is high

Low-emissivity (Low E) glass

Low E glass is made with a special thin coating on its surface. It provides high energy efficiency by deferring infrared and UV light from your windows and reflecting interior heat back into your home where it is needed.

Low E glass is ideal for:

  • Greater reduction in energy costs
  • Additional UV protection
  • Better heat insulation in your home

Self-cleaning glass

As the name suggests, this is a type of glass that can clean itself. There are two options:

  1. Hydrophobic: The glass is applied with a chemical coating that repels water from the surface, taking dirt with it.
  2. Hydrophilic: The glass is sprinkled with titanium dioxide atoms during the manufacturing process to create a special coating that causes dirt to be dissolved by sunlight through a process called photocatalysis.

Self-cleaning glass is ideal for:

  • Locations with high levels of traffic and pollution
  • Hard-to-reach windows
  • Cost-savings in terms of cleaning

Noise reduction glass

Noise reduction glass is the recommended choice if you live in an area with lots of noise pollution, such as near a main road. Similar to laminated glass, this is made by joining two layers of glass with a layer of PVB, which provides noise reduction. Furthermore, you can vary the thickness of the glass to get better results. Typically, a noise reduction of 34 decibels (90%) is measured.

Noise reduction glass is ideal for areas with high volumes of traffic and noise pollution.

How much money can I save with double glazing windows?

Based on the energy rating of different double glazing windows, the estimates below are what you could save on your heating bills each year compared to single glazing.

Window energy ratingDetached houseSemi-detached houseMid terrace houseBungalowApartment



















Double glazing windows FAQ

Do double glazing windows keep heat out?

The insulating gas in the double-glazed unit creates a thermal cushion and insulation effect, reducing the transfer of heat between the inside and outside panes of glass. This means the cold air from the outside glass pane doesn’t reach the inside glass pane. Here are some things you can do to further reduce heat transfer:Increase the spacing between the glass panesUse Low-E glassUse argon gas instead of air in the cavityInstall a reflective e-coating on the glass pane

Do double glazing windows reduce noise?

Sounds are created by vibrations. When sound waves pass through an object, they lose energy, which dampens the sound. Compared to single-pane windows, double-glazed windows have an additional layer of glass and a gas layer, so they can reduce sound more effectively. To further reduce noise, here are some things you can do:Increase the thickness of the glass paneVary the thickness of the outer glass pane and inner glass paneUse triple glazingUse acoustic glass or laminated glassIncrease the gap between the glass panesA standard double-glazed window with 4 mm glass panes and a 12 mm air space can provide you with a 19% reduction in noise when compared to a standard 3 mm single-pane window. Different configurations are available if noise reduction is your goal, with some offering up to 57% noise reduction compared to standard single-pane windows.

Can you repair blown double glazing windows?

If you’re wondering if your double glazing is blown, be sure to look out for these signs:Mist forming in the middle gas layerCondensationLeaksCracks or chipsDraughtsLeaving blown double glazing untreated could cause health problems due to mould—and hefty repair bills. However, installers do offer warranties. Be sure to check the terms before purchasing your double glazing, so you know you can get any necessary repairs completed with minimal cost should you need to. You could consider DIY kits if your warranty period has expired. Keep in mind that some work is required. Don’t attempt it if you are not confident, as it may make the situation worse. We recommend getting professional advice from your installer before carrying out any repairs. In some cases, depending on how severe the problem is, you might need to replace the window.

How long do double glazing windows last?

Double glazing is designed to last between 25 and 30 years and has been known to last longer on occasion. However, it should be noted that this lifespan is based on the following:Quality of installationQuality of manufactureWeather conditionsLocation

How do you clear misted double glazing windows?

A common problem with double glazing is misting. Here are some tips for how to clear it:Keep your home well ventilated by opening windows and checking that the window drip vents are open.Use extractor fans to help remove excess moisture from cooking.In the bathroom, close the door, open the window, and turn on the extractor fan. This helps reduce moisture spreading to other parts of your home.Keep chimneys and air bricks clear to allow airflow through your property.Use a dehumidifier to reduce moisture in your home.

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