How much does a glass extension cost?

If you are planning on adding a glazed extension, calculating costs is the place to start and our guide will talk to you through exactly what to budget for.

Glass box extension on a period property
(Image credit: van Ellen + Sheryn)

A glass extension is as dreamy as extensions come. Like any extension they add space to your home, opening it up and allowing for a more flexible way of living that we all love. But glass extensions also bring in floods of natural light, connecting your home with your outside space in a way that no other type of extension could. 

Expanses of glass make a real design statement too, whether you are adding them onto a modern home or creating that gorgeous contrast with a period property. Plus they can work in smaller spaces, so you don't need acres of room to add a glazed extension and reap the benefits of all that extra light.

When it comes to cost, glass extensions tend to be more costly than your average extension or conservatory. Building with large pieces of glass is not cheap. However, you can still add a glazed extension on a  tighter budget, we'll talk you through some options here. But it is always important to establish your budget before you start planning your project. So we've broken down all the costs you need to know about, plus plenty of examples of beautiful projects so you can get inspired (and see what you can potentially get for your budget).

Glass box extension ideas

(Image credit: IQ Glass)

How much does a glazed or glass box extension cost?

On average a glass extension costs £3,000 per m2 for just the glazing. For a glass box extension prices start from around £14,000 for a small glazed extension and go up and over £80,000 for a large project. 

These prices are more than your average extension because glass is an expensive material and can be tricky to install, especially in large expanses. However, there are ways to can add a glass or partially glass extension and stick to a tighter budget and we will cover those here. 

'If you are looking for a high-quality glass extension that maintains a comfortable internal temperature all year round and provides high levels of security whilst maintaining minimal profiles, then probably around £30k upwards you’d be looking at for one that performs as well as it looks.' explains Shannon Normoyle from IQ Glass.

'With glass extensions, the temperate in the internal living space need to be considered carefully, glazing options such as heated glass or solar control glass will be more expensive but it will ensure the space is comfortable and usable all year round. Again one of the main factor in this is the size of the glass extension, obviously the bigger they are the higher the overall cost will be.'

Nikki’s elegant, light-filled extension took hard work, time, plenty of saving and attention to detail in the design

(Image credit: Malcolm Menzies)

There are factors that will affect the over all price of your project. The materials used being the main one – the type of glass you use and the material used to the frame will impact on the price. Alluminum frames for example will be cheaper than steel and costs will go up if you want to go for solar control coatings or heated glass for your extension.

The type of opening, should you want them, will add to costs too. Adding bi-fold doors to a glass extension would costs around £2,000, depending on the size and design and if you want something more seamless like sliding doors you would be looking at paying almost double, around £3,800, again size dependent. 

A cost that you might not think about it if you would have to hire a crane to move the large glass panels around your space, this could add an extra £5000. Plus, you will also have to add on the costs of hiring an architect and a structural engineer for your project. This is usually anywhere between 3% and 7% of the total cost of the project and a structural engineer would be somewhere between £500 and £1000

Plus there's the costs of obtaining planning permission. If you want more details on costs and how to apply, check out our guide to planning permission. You can also get a idea of extension costs that are more specific to your project using our extension cost calculator

How much does a glass roof extension cost?

Glass extension ideas

(Image credit: Malcolm Menzies)

Opting for a glass roof extension, rather than something that's totally glazed is a more affordable option that will still add space and bring in light. Adding a flat glass roof to a brick-built extension would start from £2,500. If you were building a side return extension with a lean-to glass roof made up of pieces of glass rather than one single piece to a brick-built extension, costs on average £3,000. So both of these are more budget-friendly option. 

If you want a seamless look with a roof made up of a single piece of glass than than the length of your extension this will cost more, prices start from around £5,000. For this kind of project it would also be likely you would need to hire a crane if the glass cannot be walked through, or safely around the house. 

Can you add a glass extension on a budget?

Sarah Brooks glass box extension has transformed the kitchen in her London home

(Image credit: Malcolm Menzies)

Whilst it is possible to add a glass extension on a budget, you are still looking at spending a minimum £14,000 for a smaller extension or a small glazed side return. 

You could also save money on the materials you use, plus the design your go for – it tends to be the larger the pieces of individual glass the more expensive the project, so working with smaller pieces that sit in a slim framework would be a more affordable option. You'll still reap all the benefits of adding a glass extension – the light, the space – but you might not have that totally frameless look that's popular with these kinds of extensions. 

'There are a few ways, for example, aluminum framed glazing systems tend to be more cost-effective than steel-framed glazing systems, so if you were designing a glass extension with sliding doors, opting for the aluminum ones would save some money.' says Shannon. 

'Ultimately though when it comes to glass extensions you don’t want to cut corners. These types of living spaces can become the heart of the home when designed correctly, and you want to ensure that the finished look is modern and minimal, but also that the space is usable all year round. You wouldn’t want to cut corners and end up with a space that overheats in the summer and is cold in the winter.'

Nikki’s elegant, light-filled extension took hard work, time, plenty of saving and attention to detail in the design

(Image credit: Malcolm Menzies)

If you are looking for a more budget-friendly option, you might want to consider adding a conservatory to your home. You likely won't get that very sleek, contemporary look as you would with a fully glazed structure, but if you want to add space and light on a higher budget, prices to add a conservatory start from just £2,000 for a PVC kit but for £30,000 you could get something really beautiful and bespoke. 

Does a glass extension add value to your home?

period property cottage with glass sliding doors by IQ Glass

(Image credit: IQ Glass)

On average a glass extension will add around 7% to the overall value of your home. A brick-built kitchen extension that created an open plan layout could increase value by up to 6% and a larger conservatory could add 5%. So in terms of return on your money a glass extension would be a good investment, despite the high prices. 

Hebe Hatton

Hebe joined the Real Homes team in early 2018 as Staff Writer before moving to the Livingetc team in 2021 where she took on a role as Digital Editor. She loves boho and 70's style and is a big fan of Instagram as a source of interiors inspiration. When she isn't writing about interiors, she is renovating her own spaces – be it wallpapering a hallway, painting kitchen cupboards or converting a van.