There’s never been a wider choice for homeowners when purchasing brand new double glazing. We’re all very familiar with the different types of frame – uPVC, timber, and aluminium. We also know the type of window we want for our homes too – casement, sash, tilt and turn, and so on. But how much do you know about the types of glass used in double glazing?
You might be surprised to hear that there are seven main types of glass used in double glazing installations in the UK:
- annealed (or float) glass
- tempered (or toughened) glass
- laminated glass
- low E glass
- self-cleaning glass
- noise control glass
- fire protection glass
The best way to find out which is the right type of glass for you is to speak with a professional and experienced installer. Here at CompareCompanies, we work with hundreds of reputable and established double glazing companies with strong and reliable track records of customer satisfaction, quality materials, and industry-leading, professional installation.
It’s even better to speak to three or four at once because encouraging competition between installers has been shown to bring down the size of the quotes you receive by up to 40%. We’ll put you in touch with these installers at no charge, and you’re under no obligation to accept any of the quotations you’re offered.
Annealed (or float) glass
Annealed glass (or float glass) is manufactured via the Pilkington process, the process that most modern windows are made from. It involves floating molten glass on a facet of molten tin (or another metal), and this method gives the glass the same thickness throughout and the desired surface flatness. Every other type of glass mentioned in this article starts off as annealed glass.
Float glass is the least expensive type of glass on the market, but its affordability does not affect its suitability for use in double glazing, triple glazing, or in conservatories in people’s homes.
Annealed glass is very strong and can withstand six thousand pounds per square inch of pressure. To put that into context, six thousand pounds per square inch of pressure is equivalent to the weight of a grand piano concentrated into one square inch.
How is annealed glass so strong?
Because of the way that double glazing is manufactured, it’s very difficult to break or smash it no matter what type of glass it’s made from, and that includes competitively-priced annealed glass.
This is how double glazing works. Within a double glazing frame, there are two panes of glass held in position, between which is a gas, like argon, which is heavier than the air in the general atmosphere.
The heaviness of the gas between the panes makes double-glazing really strong. If something is thrown at double-glazed windows with force, the argon pushes back against the hitting object. This gives double glazing enormous strength, soundproofs against noise from the outside and insulates your home.
Annealed glass is thin, light, strong, and malleable – those qualities together with its competitive price make it the most popular choice for British homeowners.
Tempered (or toughened glass)
Up to 25% more expensive than standard glass, tempered or toughened glass is popular among homeowners whose budgets can accommodate the extra expense because it has a longer lifespan. It generally keeps its optimum condition for up to 5 or 10 years longer than annealed glass, so you don’t have to replace it as often. Therefore, it may end up costing you less over time.
Toughened glass is manufactured by placing a pane of annealed glass in an oven set at 620°C. After a short time in the oven, it’s then immediately and quickly cooled in water.
As opposed to standard glass which, if it breaks, shatters into long shards, toughened glass breaks into very small pieces, putting your family (and particularly your children) at a much-reduced chance of sustaining an injury. Manufacturers of shower doors and glass-covered tables choose tempered glass for this very reason.
Toughened glass can withstand twenty-four thousand pounds per square inch of pressure before breaking – that’s the same as 1.7 times the weight of a tyrannosaurus rex, or the anchor of a cruise ship, placed on one square inch of the window pane.
When is tempered (toughened) glass required?
There may be a time when an installer insists that you use toughened glass in your home. Current Building Regulations stipulate that tempered glass must be used for:
- any window fitted 800mm or lower from floor level,
- any window 300mm or less from a door and up to 1500mm from the level of the floor, or
- on any glazed door up to 1500mm from floor level
However, please bear in mind that, when your toughened glass double glazing is being fitted, you should make sure that your installer drills the minimum number of holes needed into a pane because these screws significantly weaken the strength of the glass.
Despite being up to 40% more expensive than standard glass, laminated glass is even safer than tempered glass when shattered – it’s safer because of a special interlayer made of plastic that covers the entire pane. The interlayer is made out of ethylene-vinyl acetate or polyvinyl butyryl, and this interlayer holds the glass in place if your window is broken. This further reduces the chance of injury to family members.
As well as being heavily used in the double glazing industry, laminated glass is also used on shopfront windows (where broken glass on the floor would cause a risk to shop staff, customers, and passers-by) and on your car windscreen.
Laminated glass offers additional protection against forced entry burglary because, when broken, the plastic interlayer holds so strongly in place that there is not enough room for a thief to climb through it. In addition, in recent years, some laminates used on double glazing offer enhanced protection against UV rays, protecting the colours of your carpet and your furniture from prolonged sun exposure.
Low E glass
“Low energy” or Low E glass is specially manufactured for homeowners wishing to save as much money on their electricity and gas bills as possible, by reducing their reliance on their central heating and cooling systems.
Low E glass generally costs up to 25% more expensive than standard glass. However, if you live in a large property and your heating bills are high, the amount you save every year on your utility bills may be equal to or more than the premium you pay for your Low E glass.
Low E glass is coated with a transparent metal film, which reflects heat from your rooms back into your home and allows light and heat from outside to pass through the panes. While all modern, energy-efficient double glazing offers these features, the low E does it better because of this special metal film.
Depending on which company supplies your installer, there are two types of Low E glass currently on the market in Britain:
“Hard coat” method
If you’re offered a “hard coat” method, your double glazing panes will be manufactured by Pilkington. When a pane of glass is hard-coated, the manufacturer adds a very thin layer of molten tin onto the sheet of glass while the glass is still molten hot. The molten tin and molten glass then fuse, meaning the tin becomes incorporated into the final pane. As a result, they have a stylish grey or light blue tint to them.
“Soft coat” method
The “soft coat” method is offered by Saint Gobain. With soft-coating, atomised tin, zinc, or silver is released into a vacuum chamber along with the pane of glass and a gas with an electrical charge. The atomised metal is then sprayed onto the surface of the pane, similar to the way gold or silver-plating is added to jewellery. Only one side of each pane is sprayed and, when your double glazing frame is being manufactured, the sprayed sides always face inwards towards the inert gas in the layer between.
Up to 25% more expensive than standard glass, self-cleaning glass’s stand-out property is that the glass facing the outside of your building will clean itself, whether it’s been raining or not.
Toothpaste and white paint contain an element called titanium dioxide. Self-cleaning glass uses this same element. It’s placed on your window panes during manufacture as a thin layer. In fact, the layer is so thin that it’s completely transparent and your window still lets in nearly as much light as a standard annealed window – 95% or more.
How does self-cleaning glass work?
When the UV rays of the sun come into contact with the titanium dioxide, the electrons within the film are stimulated, which causes it to extract water molecules from the air and bring them towards the window’s surface. When the water and titanium dioxide come into contact, there is a chemical reaction that creates something called “hydroxyl radicals”. Those radicals start to break down the composition and structure of anything organic on your window. All of the marks and dust on your window are then washed away when it starts to rain.
Self-cleaning glass also works when it doesn’t rain. The titanium dioxide still grabs water molecules from the air and the water starts to spread evenly over the surface of your windowpane, like a film. Over time, gravity starts to force the very thin film of water down your window, washing away the broken-down dust, marks, and any other matter.
Please be aware that you will still have to clean the glass on the inside of your home and that self-cleaning glass is of limited use in areas with high airborne salt or pollutant levels.
Noise control (acoustic) glass
Noise control glass, often referred to by installers as acoustically-insulating or acoustic glass, is ideal for homes underneath flight paths or near very busy roads. Noise control glass uses a special interlayer manufactured to reduce the level and the range of noise reaching the inner pane of your double glazing. Independent tests have confirmed that there is up to a 75% reduction in sound and sound levels when noise control glass is installed.
The interlayer also provides the same shatter-proof protection offered by laminated glass, for extra safety around your home.
Noise control glass is up to 25% more expensive than standard glass, so you may wish to choose to use it on windows facing a busy road. But if the back of your home is much quieter, you may save money by choosing a different type of double-glazing for less noisy areas.
Fire protection glass
Fire protection not only holds back fire, it holds back smoke too. Smoke is, in many ways, more injurious and deadly than fire, and fire protection glass can be manufactured to provide protection for 30, 60, 90, 120, or 180 minutes – ask your installer for advice for your situation.
Whereas normal glass shatters at 500°F, fire protection glass offers protection at temperatures up to 1,600°F. It does by using clear resin interlayers which are placed between the panes of glass in your frame. The interlayers are fire-resistant and the panes of glass used are much thicker than the panes in more standard installations. A by-product of the thicker glass and the additional interlayers is enhanced protection from the sun’s UV rays and against noise from outside.
Get a range of quotes for double glazing you’ll love
There’s more choice available to you than ever before with double-glazing for your home. Both the technology and the manufacturing processes have significantly progressed in the last 20 years, meaning that there’s far more choice available to homeowners and at lower prices.
The type of glass you choose for your double glazing installation is important. You don’t have to choose the same type of glass for every window in your home either – the choice is truly in your hands.
At CompareCompanies, we put homeowners in touch with experienced, qualified, and certified double-glazing companies across the UK – all of our installers are FENSA or CERTASS registered. Our service is free and there’s no obligation on you to accept any quote given to you by our chosen installers.
By getting companies to compete with each other for your business, you could save up to 40% on your installation. And because double-glazing is such a major investment in your home and in your family’s comfort and security, it pays to work with a company you feel you can trust at a price you can afford.
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