Types of double glazing

There are a dizzying array of different types of windows and doors, as well as materials and finishes.

From sash to bay windows, and sliding to French doors, here's what you need to know to help you choose what's best for your home.

We recommend asking a few double glazing companies to come to your home to give you advice, explain the types of products they have available, and to get an idea of cost.

What type of double glazed windows are right for your home?

Our gallery shows the various types of double-glazed windows and materials. Scroll down below to see more information about each.

The images of double-glazed windows and doors above are from national companies Anglian, Everest and Safestyle. 

Double glazed casement windows

Casement windows are attached to the frame with one or more hinges. They typically open to the side, but can also be hinged at the top or bottom, making them 'tilt and turn' windows – more on these below.

They usually open inwards, which generally makes them easier for cleaning, but limits what you can store or display on the windowsill. 

They are held open by 'casement stays' – small metal bars that open and close in a scissor motion. 

Casement windows are often uPVC, but can also be made of timber and aluminum. Many companies also offer different colour options.

Casement windows can either stick out from the frame or sit flush to it.

Double glazed sash windows

Sash windows typically open by lifting vertically up or down. 

They can be either:

• single-hung windows – where just one pane moves, typically the bottom, while the other is static
• double-hung windows – this means both panes can be moved, one up and the other down.

You can also get tilt-and-turn versions, and they come in a range of different materials and finishes.

Sash windows are a great way to add a traditional or authentic feel to a period property. Because they don't hinge in or out, they can be useful if space is tight.

Old, single glazed sash windows had a reputation for not being particularly energy-efficient. But modern designs employ the same double glazing technology as other windows. 

In hot weather, double hung sash windows can be very effective for ventilating a room when both top and bottom are open.

Bay windows

Bay windows stick out from the wall of the house. They either sit in a curved bay that gives some extra floor space, or as a protruding window bay with a deep sill.

They usually house three or more windows, and you can have any type, material or finish. As well as being a great design feature, they add extra space to a home. The two side windows allow more light in as the sun moves through the day.

Tilt and turn windows

Windows with a tilt-and-turn hinge can be tilted open. Different designs allow you to open the windows to varying degrees and in different directions. 

They typically open slightly, so that they can be left ajar, but some can tilt up to 90 degrees.

Some come with notched catches to hold them open at different points. As they can be locked partially open, they're a secure way to allow some fresh air into your home. 

You can also get dual-turn windows, where two windows sit one on top of the other and both tilt open. Some double glazed doors come with the ability to tilt, too.

Double glazing window frame materials

uPVC window frames

The most common type of window frame for double-glazed windows is uPVC (unplasticised polyvinyl chloride, to give it its full name). It is up to three times cheaper than traditional wooden frames. 

It's also recyclable, durable and energy-efficient.

uPVC window and door frames are available in a variety of colours and finishes, including wood effect, though they're most commonly white. uPVC is easy to keep clean, too, requiring little more than a wipe down with a soft cloth and a spot of washing-up liquid every now and again.

Wooden/timber window frames

Traditional timber is more expensive than uPVC, but many people feel it's worth the extra spend, particularly in traditional or period-style properties.

While timber windows do need maintenance, they can last a very long time if properly looked after.

Aluminium window frames

Aluminium is very strong, so its windows are durable and low maintenance. It's also slimmer and lighter than other materials, so can give a sleek, modern look.

Although you'd assume aluminium windows are grey in colour, many manufacturers offer lots of different options.

Which? members can find out more about the cost of different types of windows and materials, as well as other price considerations, by visiting our page on double glazing costs.

Triple-glazed windows

Triple-glazed windows have a third pane of glass, so they should make your home warmer and more sound-proof than double-glazed windows. 

Some companies also use different types of gas between the panes to further prevent heat loss and Low-E glass to reflect sunlight inside.

We asked nine double glazing installers endorsed by Which? Trusted Traders whether they think triple glazing is worth the extra spend. The unanimous answer was: no. 

Overall, they thought that it may be worthwhile in certain circumstances, but not for most. They said it's expensive, can damage windows and is much more expensive to replace.

We asked installers: is triple glazing worth it?

• ‘It is usually not worth spending extra on triple glazing unless the unit thickness itself is increased. For example, 28mm triple glazing offers very little improvement on 28mm double glazing but 44mm triple might be a better option.’ Jack Warren, Glazerite Lichfield.
• 'Generally triple glazing is not worth it. They are more expensive to replace and have less longevity - they are more likely to "blow" earlier (typically around 10 years), causing condensation or misting. The savings in heating bills in no way balances out the cost. Triple glazed glass units also weigh alot more and if you have chosen a top hung design, the weight will often cause the window to sag and catch when it is opened and closed.' Jacob Gourd, Ideal Glass.
• 'In the majority of domestic replacement cases I would say no. I don't think the improved u value is worth the extra cost - the pay back period, in terms of offsetting against heating savings, is too long. The glass units are of course more expensive to replace should one get broken too.’ Phil Brown, Salop Glass & Glazing.
• 'For most homes, modern high-performance double glazing is more than sufficient. Triple glazing can help in specific situations but isn’t always necessary and can negatively effect the durability of a window.’ Tommy Rose, Barnet Window Company.
• 'These units are much more expensive to replace when they break down. Many customers will replace the broken down unit with normal double glazing, to save money.’ Daina Rawlings, The Window Doctor Care and Repair Services.
• 'Triple glazing may be worth spending extra money if you live on a very busy road or in a very cold and windy part of the UK, as it can improve insulation and reduce noise. But if you live in a typical suburban town, you most likely only need double glazing.' James Gaft, Balhousie Glazing.

If you're keen on getting it, but the cost is prohibitive for your entire house, think about selectively using triple glazing in the rooms that get coldest or suffer worst from external noise.

Double glazed doors

Double-glazed doors are a good way to let light into your home. The gallery below shows the various types of double-glazed doors. Scroll down to see more information about each.

Patio sliding doors

Patio sliding doors slide open. Typically one moves while the other stays static, but you can have both sliding. 

They're a good space saver, as they don't have to open into your garden or home's floor space. Sliding doors can be uPVC or aluminium, and come in a range of colours and finishes.

Double glazed French doors

Sometimes called ‘French windows’, these glass doors open out like casement windows. Although both can open, you can choose to have one open at a time.

As well as aluminium and uPVC, French doors can come in wood, too. Again, there are lots of finishes available.

You might want to use 'stays' – hooks to ensure the door stays open and doesn't fly back or slam shut in the wind.

Bi-fold doors

Bi-fold doors are a set of two or more glass doors that fold back onto each other in a concertina. With these types of doors, you won't need anything to hold them open as they automatically stay where you've opened them.

They come in aluminium and uPVC and various colours. 

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What is secondary glazing?

Secondary glazing involves fitting a second layer of glass inside your existing windows. It isn’t as effective as full double glazing, but it could still save you some money on your heating bills – and it's much cheaper to install.

It could also be a good alternative for homes that can't have double glazing – if you live in a listed building, for example. 

Where to buy double glazing

Well-known national double glazing companies include Anglian, Everest and Safestyle - all three are owned by the same parent company. 

You can also choose an independent double glazing company in your local area. 

If you're having an extension or building a new home, you can also use the independent builder or joiner you're already coordinating with for your project. 

Some DIY stores, such as B&Q, also sell double glazing, so you might want to buy it yourself and then have a builder install it for you.

Find out how much you should expect to pay for double glazing to avoid being overcharged.

B&Q

B&Q sells double-glazed windows and sliding patio doors in both uPVC and white-finished timber. Brands include Velux, Site and Keylite.

Screwfix

You can buy double-glazed windows and skylights from Screwfix.

Windows are available in a wide range of formats and sizes, in both uPVC and white-painted timber. Brands on sale include Crystal (not to be confused with Crystal Windows and Doors of Romford) and Jeld-Wen for standard double-glazed windows, while they stock Keylite skylight windows.

Wickes

Wickes sells double-glazed windows and roof windows from Euramax, Keylite and Velux. 

French patio doors are available from Wickes in several sizes and designs, from brands such as Jeld-Wen and Jci.

Independent double glaziers

Use our Which? Trusted Traders search tool to find a reliable, independent trader to install your new double glazing. To find out more about the comprehensive assessment a company must pass to become a Which? Trusted Trader, read our guide to independent double glazing companies.