What Is a Double-Glazed Window?

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Glass has long come between us and the outside world, protecting us from rain and snow and keeping us warm, all while letting in light. Glass is a simple invention that has worked efficiently for hundreds of years. So what could be better than this miraculous sheet of glass? How about two sheets of glass? That’s where double-glazed windows come in.

What Is a Double-Glazed Window?

A double-glazed window is a window with two sheets or panes of glass.

The term glazing derives from the Middle English word for glass. People who repair window glass are called glaziers. If you hear the term glazing, it will usually be when some window manufacturers refer to their window designs as being single-glazed or double-glazed.

A single-glazed window has one sheet of glass. A double-glazed window has two parallel and separate sheets of glass. In extreme climates, triple-glazed or triple-paned windows are sometimes recommended.

The term glazing is infrequently used by major window manufacturers anymore to describe their windows. The company might use the terms glass, panes, or sheets. Often with double-glazed windows, the number of sheets of glass is not even mentioned in the product literature since double-glazing is standard.

In the window industry, the double-glass assembly is sometimes called an IGU, meaning insulated glazing unit or insulated glass unit.

Advantages of Double-Glazed Windows

Double-glazed insulated panel windows with two panes of parallel glass offer a significant advantage when it comes to the energy efficiency of the window. Double-glazed windows are now standard for both new-construction windows and replacement windows.

The idea behind multiple glazing is that the two panes of glass, including the intermediate buffer zone, provide a better barrier against outside temperatures than single-paned windows. In fact, the glass itself isn’t much of a thermal insulator. Its value is that it can seal in and maintain a buffer.

Double-glazed windows can be engineered so there is simply dead air space in the gap between the window panes. But today, it is more common for that space to be filled with inert gas, such as argon or xenon, which increases the window’s resistance to energy transfer.

Triple-glazing (three panes) is used in very harsh climates to further improve the insulating value of a window. Other measures can also help increase the energy efficiency, such as applying thin coatings of special materials to one or more faces of the glass. These low-E windows (the term stands for «low emissivity») have thin transparent coatings of a metal oxide or silver applied to one or more of the glass surfaces to further reduce the energy transmission.

Double-Glazed Windows’ Energy Efficiency

The insulating value of a window can be measured in a number of different ways. Common is the R-value system, a measurement of material’s resistance to energy transfer. The higher the R-value, the greater the resistance and the higher the insulating value.

The insulating advantage of double-glazing becomes obvious from the tested R-value of various window designs:

• Single pane: R-value 0.9
• Double pane with .5-inch air space: R-value 2.04
• Triple pane with .5-inch air space: R-value 3.22
• Double-pane with argon and low-E coating: R-value 3.846
• Triple-pane with argon and low-E coating: R-value 5.433

By comparison, a standard two-by-four stud wall with batt insulation and wallboard and wood siding has an R-value of R-12 to R-15. Window manufacturers are now developing technologies that allow windows to approach the R-value of the walls themselves.

Improving Double-Glazed Windows’ Efficiency

No matter how well-designed they might be, windows are always a major point of energy loss in a home, when compared to other building elements. There is simply no comparison between the most energy-efficient double-glazed window and even an ordinary wall system. To help improve windows’ efficiency:

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Double Glazed Windows

Double glazing is ubiquitous throughout the UK these days, for good reason! Cheap, efficient, easy to install and readily available, this will be a great choice for people who have been living with single glazed windows. Read our article for price points and all the information you need!

How much does double glazing cost?

The number one concern people have about installing double glazing is the cost. You will be wondering how much new double glazed windows will cost you.

Thankfully we are here to provide you with a concise but comprehensive overview of how much it should cost you to install double glazing. We break down the costs by material used and give you specific price points for the most common types of windows.

uPVC windows

Pricing is for Standard A rated Windows, cost of materials and installation only.

Cost of uPVC Windows (materials + installation)

Type of home Number of Bedrooms Windows needed Expected cost of Casement style uPVC Windows Expected cost of Sash style uPVC Windows Flat 2 4 windows £1,450 — £1,700 £2,400 — £3,200 Terraced 2 5 windows £1,800 — £2,250 £3,000 — £4,350 Semi-detached 2 7 windows £2,500 — £2,800 £3,700 — £5,200 Semi-detached 3 9 windows £3,200 — £3,500 £4,400 — £6,600 Detached 3 12 windows £4,200 — £4,700 £6,200 — £7,550 Detached 4 15 windows £5,300 — £5,800 £7,200 — £9,400

Wooden windows

Pricing is for wooden style double glazing windows, cost of materials and installation only.

Cost of Wooden Windows (material + installation)

Type of home Number of Bedrooms Windows needed Expected cost of Casement style Wooden Windows Expected cost of Sash style Wooden Windows Flat 2 4 windows £2,400 — £2,800 £4,100 — £5,500 Terraced 2 5 windows £2,800 – £3,050 £5,150 — £5,700 Semi-detached 2 7 windows £4,200 — £4,500 £6,500 — £8,000 Semi-detached 3 9 windows £5,500 — £6,200 £7,700 — £11,500 Detached 3 12 windows £7,850 — £8,650 £9,500 – £13,600 Detached 4 15 windows £9,350 — £10,100 £12,300 — £16,000

Aluminium windows

Pricing is for aluminium style double glazing windows, cost of materials and installation only. Sash aluminium windows are very rare, so we omitted them.

Cost of Aluminium Windows (materials + installation)

Type of home Number of Bedrooms Windows needed Expected cost of Casement style Aluminium Windows Flat 2 4 windows £2,400 — £2,800 Terraced 2 5 windows £2,800 – £3,050 Semi-detached 2 7 windows £4,200 — £4,500 Semi-detached 3 9 windows £5,500 — £6,200 Detached 3 12 windows £7,850 — £8,650 Detached 4 15 windows £9,350 — £10,100

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What are double glazed windows?

Double glazing means that you fit a window space with two panes of glass instead of the traditional one. The gap between the two panes will contain either air or an inert gas such as argon to ensure a more reliable barrier against temperature fluctuations outside.

Double glazing works much the same way as a wool jumper.

Your body generates heat and as it makes its way through the jumper, the fibres of the wool are hollow and trap heat in this small air cavity which keeps you warm and cosy.

The same goes for windows. Heat escapes through single pane windows as the glass is an excellent conductor of heat, and with nothing to keep the heat in, it escapes fairly easily.

With two panes, the cold air is trapped in the inert gas (usually argon) and does not enter your home. You will feel comfortable and warm with two panes of glass between you and the great outdoors.

What are the benefits of double glazing?

Saving money

Heating and cooling your home is getting more and more expensive as energy prices for gas and electricity steadily rise. An average household fuel bill in 2014 was over £1,150. Get lower energy bills by replacing faulty windows with insulating double glazing.

You will increase the resell value of homes when you fit double glazed windows, with buyers demanding better insulation in new and old buildings.

Better for the environment

Everyone is more environmentally focused nowadays. We pay much more attention to renewable energy sources and products that waste less power. Double glazing makes your home more energy efficient, heating your home in the winter and cooling it down in the summer.

Consider this your small – but welcome – contribution to the protection of the earth. Insulate your home well with new double glazed windows.

Healthier living

It is common knowledge that prolonged exposure to a cold and damp environment leads to health complications in the future, especially for the very young and the elderly. With double glazing installed, homes are warmer, healthier environments to live in.

Keep your family warm and healthy with effective double glazing.

Listed home? No problem

Many homeowners living in heritage listed homes will know that you either cannot make changes to the existing facade or is very complicated and costly. Secondary glazing, which is similar to double glazing is an option.

You can install secondary glazing on the inside of the building without disturbing the outward appearance. Secondary glazing is half as effective as double glazing according to many people. However, they can still provide many of the added benefits as mentioned in our dedicated section on secondary glazing.

Security

Windows are a home’s weak spot when it comes to security. One of the added byproducts to double glazing is the improved security it gives to your home. By adding two panes of glass the chances of an unauthorised entry are reduced.

There are other options available for enhanced security measures. For example, you can use a safety or laminated glass that includes a built-in layer of resin. This makes it difficult to break but also does not compromise on the clarity of the window.

Why are double glazed windows so popular?

With double glazing, the air cavity traps heat between the two panels of glass. The most common reason people get double glazing is for thermal insulation. When you want insulation above all else, you want low-emissivity windows. This is also known as Low E glass.

If the glass is Low E, it will reflect even more heat back into the house. Having double glazed windows installed with Low E glass also traps the heat generated from the sun better. This will let in the warmer UV rays without losing the majority of the heat at night.

Double glazing is widely used in both old and new houses. It provides the homeowner with many benefits including better insulation, noise reduction and low energy costs. There are many features to consider when looking at installing double glazing with varying styles such as uPVC, wooden and aluminium. There are also many other types of double glazing for specific applications in the home.

• Acoustic glass – for reducing noise
• Safety glass – for use in skylights and bathroom areas
• Fire glass – for use in fireproofing requirements
• Security glass – for added safety and security

What is secondary glazing?

Secondary glazing takes the basic principles of double glazing and applies it to homes where replacing the exterior window fitting is not an option, like with heritage listed homes.

By adding a second layer of interior glass you create an air cavity between the two panes. This reduces overall heat loss and noise.

Although secondary glazing is around half as effective as double glazing, it is considerably cheaper. This is because it is easy to install and does not require the strict weatherproofing requirements needed for the outside pane. So secondary glazing costs will be lower than installing brand new double glazing.

Replacing secondary glazed windows is also easy with no speciality tools or knowledge needed.

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