The essential guide to triple glazing

Triple glazing has become synonymous with efficiency in home insulation and responsible energy use. As the name suggests, triple glazing is a window that is made up of 3 layers of glass with 2 gas-filled cavities between the layers. Where double glazing, with its 2 panes of glass, was a significant improvement in insulation, triple glazing is the next evolution, improving window insulation by a further 50%.

But how does triple glazing work exactly and why does its installation guarantee such an increase, not only in domestic energy efficiency, but also in your home’s selling price?

Let’s look at the composition of a typical triple glazed window

A triple glazing window comprises 3 glass panels with 2 gas-filled chambers between the panels, encased in a sealed frame. The unit functions as an insulated whole, where the type of glass, its thickness, the distance between the glass panels, the type of gas in the cavities as well as the air pockets in the frame’s design contribute to its superior insulation capabilities.

The typical triple glazing unit is made up of 3 panes of 4mm glass, with the optimal gap size being 16mm between them. The thickness of the glass has an influence on the unit’s thermal insulation capabilities, but ultimately, it’s the size and fill of the cavity that has the most impact on preventing heat loss through the window.

Triple glazing uses Krypton [Kr] gas to fill the 2 cavities between the glass panes. Krypton gas has a 34% lower conductivity than air, which aids in heat loss prevention as well as providing sound insulation from outside noise. Because a triple glazed unit has 2 of these gas pockets, its heat conductivity is greatly reduced when compared with double glazing that has only 1 gas-filled pocket. Double glazing also makes use of Argon gas [Ar], which while being more cost effective, is not as thermally efficient.

The frames of triple glazing units are made up of 1 of 4 materials, being uPVC, wood, aluminium and composite frames that consist of a softwood core with aluminium cladding.

Click here to read more about the different window materials and for information on how to choose the right triple glazed windows for your home.

The style of window that will suit your home will typically dictate which material will be most appropriate, although most window styles can be manufactured in any of the materials. Even homes in conservancy areas and ones that have to comply with strict building codes, can upgrade their windows to triple glazing. Council requires that the aesthetic of a property in a conservancy area remains unchanged or at the minimum, sympathetic to the original. uPVC, with its highly customisable finish and texture options, is a great choice for these types of windows.

How is the glass different from other windows?

Triple glazing makes use of different treatments and types of glass to increase its efficiency.

Low iron glass is the preferred glass type to use in triple glazed windows. This type of glass doesn’t have the blue-green tinge seen in standard glass panels, making it appear whiter and more clear. This allows the most amount of short wave solar, or light, to pass through the 3 panels to the interior of the home.

Low E-glass (low emissivity glass) is coated with a microscopic film that reflects long wave infrared energy, otherwise known as heat. The interior pane of a triple glazing unit is coated with this low-E film, which then reflects heat back into the room instead of allowing it to escape to the outside. This ensures that any heat generated inside, remains inside.

The central glass panel comprises toughened glass. Because of its position in the unit, this pane is particularly prone to thermal stress cracking since it is exposed equally to hot temperatures from inside the home, as well as cold temperatures from outside. By toughening the glass pane, the risk of thermal stress cracking is reduced 4 -5 times compared with untoughened glass.


Triple glazing is far superior to any other window on the market. Click here to read why.

How is triple glazing manufactured?

Triple glazing windows are manufactured in a very strictly controlled environment. The glass panels are carefully inserted into an extruded or built frame, which is then carefully sealed to prevent leaks before the gas is inserted.

The frame makes up a very important part of the unit. Triple glazing frames are chambered, incorporating air pockets. These air pockets greatly contribute to the overall efficiency of the window.

The careful insulation of the window unit as a whole, is what makes it thermally efficient. The installation of the window should also be done with strict quality control to ensure that the area around the frame is sufficiently sealed to prevent air leaks, compromising the window’s efficiency.

For more in-depth information on the manufacturing processes of triple glazing, read this article.

Are there different levels of quality?


As with most things in life, not all triple glazing is created equal. For a start, you should be weary of any company claiming that they can retrofit a third glass panel onto your existing double glazing. As discussed earlier in this article, triple glazing doesn’t merely consist of 3 glass panels, but also the gas-filled cavities between them, as well as the chambered frame. Retrofitting glass then won’t have the same thermal insulation as a manufactured triple glazed window.

It is important to get a few quotes from different glazing manufacturers so that you may compare what is being offered by different companies. It’s not the only cost of the units that should be considered, but also the guarantee offered. Some companies offer lifetime guarantees on their window, while others offer conditional guarantees of 10 or 20 years. Ensure that you read all the fine print in the contract and understand exactly what is covered and what not. Look out for the guarantee on the gas seal, the frame and its moving parts, and the conditions under which cracked glass will be replaced.

The Window Energy Rating (WER) of a companies’ triple glazed windows are a great indication of their quality. The WER is based on manufacturing practices so you can trust that the rating takes manufacturing quality as well as energy efficiency into account.

Click here for our 5-point checklist to make sure that you get the best quality in triple glazing.

How thick is it compared to a conventional window?

A standard double glazing unit is 28mm thick. A triple glazed window, with its three 4mm glass panes and two 16mm Krypton-filled gaps, comes to a total of 44mm. This is a significant increase in thickness, but one that an average wall can still easily accommodate.

The added weight could be another consideration. Double glazing typically weighs 20kg/m², but with the added glass panel, triple glazing comes in at around 30kg/m². This means that a standard window measuring 400mm x 1200mm will weigh 9.6kg as a double-glazed unit, but 14.4kg as a triple-glazed unit, which is a weight increase of 50%.

Structurally, the increased weight of a triple glazed unit is rarely cause for concern. Where the windows become really big however, installation and handling of the unit may be a bigger issue than the weight of the window, necessitating the use of mechanical equipment and increasing the cost. To find under what circumstances your property will need additional structural support for triple glazing, read this article.

Will they fit in conventional window frames or do they need special and more expensive frames?

Triple glazing cannot be retrofitted onto your existing window frames. Triple glazing windows are manufactured as complete, sealed units and therefore require frames that accommodate 3 layers of glass and 2 gas-filled spaces between them.

Most triple glazing installers will remove your existing windows including frames, and dispose of them environmentally responsibly.


Are triple glazed windows right for every situation?

Triple glazing is a safe, efficient and financially viable option for any domestic environment that wants improved energy efficiency, increased sound insulation, zero internal condensation and draughts, and an overall increase in interior comfort levels at home.

But who should consider installing triple glazing and are there circumstances under which it is not the best option? Click here for more information.

What’s the difference between double glazed and triple glazed?

Aside from the obvious structural difference between having windows with 2 panes of glass versus 3 panes, the properties of double and triple glazing are vastly different.

Property Double Glazing Triple Glazing
Thickness 28mm 44mm
Gas Argon [Ar] Krypton [Kr]
Weight 20kg/m² 30kg/m²
Cost / m² * £200 - £460 £380 - £550
Return on Investment 77 years 45 years
Annual Energy Cost Saving £65 £163
U-Value (thermal heat loss) 1.4 - 1.1 0.7 - 0.5
G-Value (solar heat gain) 0.63 - 0.53 0.55 - 0.47
R-Value (Resistance to Heat Transference) 3 5
Window Energy Rating (WER) A to A+ A++



Read this article for a full break-down of the 11 biggest differences between double- and triple glazing.

How much money can a triple glazed window save?


When looking at the cost savings of triple glazing, it’s not only your energy bill that needs to be considered. You should also look at other contributing factors, like cost of installation and the total return on investment.

To install triple glazing in a standard 3-bedroom house with 15 windows, will cost around £7,275. The initial capital investment may be high compared with double glazing at £5,000 for the same home, but at 45 years compared with double glazing’s 77 years, the return on investment is much quicker.

The surface temperature of a window is a great indication of its heat transference. With an internal temperature of 21°C, the surface temperature of a single pane window is 1°C, of double glazing 16°C and of triple glazing 18°C. This shows a significant interior temperature increase which, as an added benefit, also eliminates interior condensation.

The average household in the UK spends roughly £663 annually on heating. Double glazing has already had a significant impact on preserving domestic heating by reducing heat loss through single glazing to 22%. A third glass panel and additional Krypton gas-filled space in triple glazing, further reduces that heat loss by 50%. This results in a saving of up to £162.50 annually in the cost of heating a home. source

Another factor that is often overlooked when considering triple glazing, is the positive effect on a home’s Energy Performance Certificate (EPC). And EPC is a compulsory rating of a home’s energy efficiency when the property changes hands or is leased. The EPC considers the home’s overall energy efficiency, which comprises the following factors:


Environmental impact and CO2 rating.


Estimated energy use, CO2 emissions and fuel costs.


The efficiency of all individual elements that influence the energy rating, like walls, roof, floor, windows, main heating source and controls, secondary heating, hot water and lighting.


Recommendations on how these different elements can be improved and how this may positively impact the energy performance rating.

The EPC has a very real impact on a home’s value. According to recent research (source), energy efficient improvements could increase your home’s value by 14% on average and by up to 38% in some parts of England. By moving a home from band G to band E, or from band D to B on the energy performance certificate, could mean that you are adding £16,000 to the sale price of the property. In some areas, this increase is even greater. In the North East, a improvement from band G to band E could increase your property’s value by more than £25,000, while that same jump in the North West could potentially add £23,000 to your home’s value.

While there is a clear financial benefit to having triple glazing installed, the benefits are also tangible in the increased comfort levels in your home. Click here for further reading on the return on investment you can expect from a triple glazing upgrade.

Are triple glazed windows a green solution?

To understand the green credibility of a product, there are various factors that need to be considered.

The manufacturing process is a big contributing factor to a product’s green rating. Not only should the carbon footprint of manufacturing be low, but the use of recycled materials is preferable.

All of materials used should also be taken into account, whether recycled, recyclable or sustainably sourced.

Triple glazing frames are made from 1 of 4 materials:


extremely durable, lightweight and resistant to corrosion, aluminium is a uniquely recyclable material that doesn’t lose any of its properties during the recycling process.


Soft-wood frames with the durability of aluminium added to the exterior frame. With the wood sourced from forests approved by the Forest Stewardship Council (FSC), this is a very green choice.


again, important to have FSC approved hardwoods. Because of its environmental impact and recycling capabilities, wood is a highly green choice.


unplasticised polyvinyl chloride is made with non-renewable fossil fuels and is therefore not the greenest choice. On the upside, however, the frames are completely down-cyclable.

The distance a window unit has to travel will also have an influence on its green status. The greater the travel distance, the less green the product. In order to choose the most environmentally responsible window then, it is always preferable to get a supplier that is close to you, and that sources their materials locally and sustainably. By choosing a local supplier, your after-sales service and maintenance will also be easier.

We have done extensive research on the environmental impact of triple glazing which you can find here.

Triple glazing can have a great impact on the efficiency and value of your home. Choose a responsible and registered supplier who will be able to give you the best advice on your window upgrade and provide you with quality workmanship and service.

Published on : 8th January 2017

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