Window Glass & Glazing Types
Originally, windows only had one job, and that was to let light into a building. The first windows were made with pieces of crown glass held together by lattice leading. Soon after, the invention of thinner and flatter plate glass led to larger squares of glass held together by wooden glazing bars.
Float glass was invented in the late 1950s, allowing for the quicker production of large, flawless glass sheets. This helped spur on the development of more advanced glazing. Double glazing became the norm from the 1970s onwards, as energy efficiency, comfort and security became more important to homeowners.
So how does double glazing work? And why are more panes of glass better?
Does a job, but offers limited sound insulation, security and energy efficiency.
A surprising number of houses in the UK are still only single glazed. Windows can be one of the greatest sources of heat loss in a home, and one pane of glass is not sufficient to retain heat. Complaints about old single glazed windows include: cold spots near the window, draughty frames, freezing cold house and noise pollution from the outside – all problems that will disappear by upgrading to new double glazing.
Installing single glazing is still a requirement on occasion where planning or conservation regulations apply. Along with timber frames, single glazing helps a property retain its period look. Another way to improve insulation under these circumstances is to install secondary glazing.
The minimum standard for new windows and the most popular choice.
Double glazing is one of the most effective ways to improve the insulation of a home, creating a warm and comfortable living environment.
In a double glazed window, two panes of glass are joined by a spacer bar, and the gap between the panes traps warm air, slowing the escape of heat from a building. In addition, the best windows introduce an inert gas such as argon gas in this space, which further limits the movement of cold air.
In the UK, all new buildings must include at least C rated double glazed windows as standard, but many companies are offering double glazing that can achieve an A or even A+ rating.
Safer, quieter and warmer windows.
Triple glazing contains a third pane of glass, creating an extra cavity which traps warm air and reduces heat loss through the sealed unit. Triple glazed windows are better at retaining heat generated within the home, whilst reducing overheating in summer.
A common misconception about triple glazing is that the improvement in thermal performance is due to the extra pane itself. However, it is more about the types of glass and coatings used, the gas filled sealed unit, and also the distance between the panes.
Is triple glazing really any better than double glazing? Ultimately, triple glazing provides next-level heat and sound insulation. It is up to 35% more effective than double glazing for thermal efficiency, and reduces outside noise by up to 35 decibels.
For some properties, triple glazing isn’t high priority, but it’s recommended for houses next to busy roads, train lines and under flight paths, or in typically colder areas.
Ambitious, but a step too far?
Some firms have tried to introduce a fourth pane of glass, but there is currently very little demand in the UK to develop quad glazing.
Colder countries such as Canada and Switzerland are already using quadruple glazed windows, but the UK doesn't plunge to such low temperatures that it would justify the need for thicker windows.
In some cases, a good triple or double glazed window can be as thermally efficient as a brick wall. Also, the cost of quad glazing is likely to outweigh the thermal benefits that an extra pane will bring.
A practical alternative to double glazing for conservation areas
There are instances when it is not possible to physically replace a window as you may live in a listed building or conservation area, for example. Despite this, you may very well feel you’re getting too much noise or cold air from outside.
Secondary glazing is an additional window installed directly inside of the existing window frame. It can help your home achieve thermal, security and soundproofing benefits, whilst remaining invisible to the outside.
Types of glass
It’s not all about the number of panes of glass – new technologies have been developed that make window glass stronger, shatterproof, clearer and quieter. Consider which types of glass would be best suited to the requirements of your windows.
Low E glass
Invisible reflective coating.
Low emissivity glass has an invisible, thin coating applied to its surface that reflects heat. It is strategically placed on the inner pane of glass to help keep heat indoors, helping to maintain a comfortable temperature.
Low iron glass
Clearer, allowing for more light.
Windows that contain low iron glass are noticeably clearer. They allow a higher level of light to pass through compared to older glass types, which sometimes have a slightly green tint.
Thicker glass, laminated or toughened to enhance security.
Security glass is available in a range of sizes and thicknesses depending on your security needs. Typically, laminated glass is 6.4mm thick (compared to 4mm for standard glass), and contains a thin plastic interlayer that prevents the glass from smashing. Toughened glass is up to five times as strong as ordinary glass of the same thickness.
Security glass is used as an outer pane in a double glazed unit, adding an extra layer of security to the window as a whole. Toughened glass must also be used for fixed lights in side panels to doors, as well as in windows close to the ground.
Sound reduction glass
Outstanding levels of noise reduction.
Sound reduction glass windows contain an inner pane that is 6.4mm thick supported by an outer pane that is an incredible 10mm thick. Together, they provide excellent sound insulation. A thin and lightweight solution to noise problems, silent windows are a powerful alternative to triple glazing.
Enhancing the character of your window and home.
Add coloured shapes, patterns and bevelled designs into the glass itself. Decorative glass looks beautiful in top hung fanlights – the top sashes of casement windows – as well as feature windows in halls and stairwells. Coloured glass is similar to stained glass windows, but it doesn’t require leading to hold the glass together.
A new version of an old classic.
Stylish strips of lead are a purely visual benefit that can be added to your window in order to make it more aesthetically pleasing. There are a range of leaded glass options that suit both modern and traditional houses, including square and diamond designs.
Maintains privacy with distinctive character.
Obscure glass creates a ‘cloudy’ effect, enhancing privacy by blurring out your home’s finer details to passers-by. Also known as privacy glass, there’s a variety of textures available, such as leaves and flowers, as well as grainy patterns.