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How to buy double glazing

Choosing double glazed windows and doors

By Liz Ransome-Croker

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Choosing double glazed windows and doors

Find out all you need to know to choose the best type of double glazed windows and doors for you, as well as the right material for your home.

With such a dizzying array of different types of windows and doors, as well as materials and finishes, it can be hard to know which ones to choose.

From sash to bay windows, and sliding to French doors, we explain the key differences between them to help you choose what's best for your home. Click on the links below to head down to the section you want.

Once you've flicked through our galleries, we'd recommend getting a few double glazing companies over to give you advice, explain the types of products they have available, and to get an idea of cost.

You can also visit our double glazing reviews to discover which was rated highest with a customer score of 84%, and which came 30 points lower with 54%.

Double glazed windows 

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

Some images of double glazed windows and doors from Anglian, Eversest and Safestyle. See how each company was rated by its customers by visiting our double glazing reviews.

Casement windows

Casement windows are attached to the frame with one or more hinges, typically allowing them to open to the side. They can instead be hinged at the top or bottom, making them 'tilt and turn' windows - you can find out more about these types of windows below.

They usually open inwards - which generally makes them easier for cleaning - but can open out. 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 - read on below for more details about window materials. Many companies also offer different colour options.

Flush casement windows (like in the picture above) are similar but sit close to the frame, so they're in line with the it, rather than proud.

Sash windows

Sash windows typically open by lifting a pane and its fame up or down. You can either have:

  • 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. Like with casement windows, they come in a range of different materials and finishes.

They're a great way to add a traditional or authentic feel to a period property. Old sash windows are known for not being particularly energy-efficient. But modern designs employ the same technology as other windows. 

Bay windows

Bay windows protrude from a house, either sitting in a curved bay that makes additional room within the house (like in the image above), or by a window section on its own out. 

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 and enable you to have panoramic views.

Tilt and turn windows

Casement windows can also come as tilt and turn versions, which means they can be tilted open. Different designs allow you to open the windows to varying degrees. They're typically used to open slightly, but some can tilt up to 90 degrees.

Some come with notched catches to hold them open at different points, like in the image below. As they can be locked partially open, they're a secure way to allow some fresh air into your home. But it's worth noting that some non-tilt and turn windows can be lock almost closed. 

You can also get dual-turn windows, where you have two windows - one on top of the other - and they both windows tilt, like in the image in the gallery. Some double glazed doors come with the ability to tilt, too.

UPVC windows

The most common type of window frame for double-glazed windows is uPVC - or, to give it its full name, unplasticized polyvinyl chloride. Not only is it up to three times cheaper than traditional wooden frames, but it's also recyclable, durable and the most energy-efficient frame type.

uPVC window and door frames are available in a variety of colours and finishes, including wood, but white is the most popular option. 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 windows

Timber is a greener option than uPVC as it's a naturally renewable material. Many people feel wooden windows look nicer and more subtle than uPVC, particularly in traditional or period-style properties.

While timber windows tend to be more expensive and need maintenance, if properly looked after, they can last a very long time.

Aluminium windows

Aluminium is a very strong material, 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 or metal in colour, many manufacturers offer lots of different options.

You can find out more about the cost of different types of windows and materials by visiting our page on double glazing prices. Once you're ready to start shopping, our page on double glazing quotes and sales tactics will help you avoid common sales tricks. 

Double glazed doors 

Double glazed doors are a great way to bring light and the outside into your home. Our gallery shows the various types of double glazed doors. Scroll down below to see more information about each.

Patio sliding doors

Patio sliding doors - which are often referred to as patio doors or sliding doors - are glass doors that slide open. Typically one moves while the other stays static, but you can have both sliding. 

They're a good option if you want to save space as they won't encroach on your garden or home. Sliding doors can be uPVC or aluminium and come in a range of colours and finishes.

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 and keep the other closed.

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

It's worth keeping in mind that with these doors you might want to use 'stays' which are essentially hooks to ensure the door stays open and doesn't fly back or 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 open them to.

They come in aluminium and uPVC and various colours. They're a typically stylish, contemporary option, particularly if they are in aluminium. 

Where to buy double glazing

There are a couple of ways in which you can buy double glazing. You can either choose a well-known, recognised double glazing company, such as Anglian, Eversest and Safestyle, or an independent double glazing company in your local area.

If you're building a new room, such as an extension, or home and will be getting new windows, you can also use the independent builder or joiner you're already co-ordinating with for your project. 

83% of the 2,155 people we surveyed in September 2018 used an independent company, builder or joiner. Our page on independent double glaziers reveals how people rated them for a number of different aspects, such as customer service and quality of products and installation.

You can use Which? Trusted Traders to find an independent near you. All companies and traders that bare our logo have been through stringent background checks and must sign up to our code of conduct, so you can be assured they're reputable.

Double glazing buying tips 

We've spoken to experts and homeowners for their tips on how to find the best double glazing and save money in the process.


Before you start getting quotes for double glazing, having a good idea of what you want and your requirements means that you'll be better informed and more in control with a salesman. 

It'll also mean that the quotation can be much more tailored to your specific needs, so you have a true idea of what you'll need to pay.

Trade shows or consumer home exhibitions are a good place to start. You'll be able to see a wide range of double glazed windows and doors in one place. 

Also, take a look at the homes in your area. What kind of windows do similar properties to yours have? Is there a type that's common in your road? You don't want your home to stick out like a sore thumb.

Remember that at some point you may sell your home, so make sure the style you choose won't put potential buyers off. 


A number of homeowners we spoke to suggested visiting companies' showrooms/warehouses. When there, ask whether the double glazing is made on site to order or bought in. This will give you an idea on how long it might take to get the products to you, and whether the company will have control over quality.  

It's a good idea to also discuss the technological benefits of different systems when visiting a showroom, so that you can get a feel for how knowledgeable and professional the company seems. One homeowner said: 


Think about warranties. Some double glazing companies offer lifetime guarantees, other 10 years. Check what the warranty covers and make sure the hardware is included - this is often only covered for one or five years.


Whether it's the buying, delivery or installation stage of your process, if you have concerns or questions, speak to the company sooner rather than later. Most things can be solved easily with time and consideration.

If you experience any problems with your double glazing company, our page on your right when buying double glazing runs you though your legal rights and the steps to follow to get things put right or your money back.