How Much Does A Glass Box Extension Cost?

Glass box extensions have become very popular recently and they make a stunning addition to any home. Using structural glass to build the entire structure, they can bring light into dark homes, and they can also add modern design to older homes. So you’ve already fallen in love with the idea – but how much do they cost?

As a starting point, a glass box extension that is around 3m x 2.5m will cost around £35-40,000 + VAT. This is to supply the glass, with two side returns and a set of doors, to a site that is prepared and ready. Options – and there are many! – will obviously add to the price, but as specialist in contemporary interior design, we can guide you through the design process. We will also handle all the regulatory requirements in-house – this may include planning permission if required.


This Islington glass box extension features on our website and it was used to extend into the area of a typical side return on a Victorian terrace house. The Grade II listed property had two small rooms on the lower ground floor before we started. The kitchen was only around 2m x 2.3m with a dining area next to it. Using structural steels to fully support the property, we removed all the internal walls to create a new kitchen and dining area that is 6m x 5.5m.

As a listed building, the property required listed building consent but here’s a surprise – conservation officers love glass structures. The new extension clearly defines the old and new. There is no doubt about what is original and what has been added. So we added wow factor to a home that was over 100 years old and kept local planners and conservation officers happy.

If you have space for a larger extension, we recently quoted for a glass extension to a home in South West London that would measure 7m in width and extended 4.5m out from the house. The supply and installation of this glass structure would be around £80,000 + VAT. Building work to prepare the site and interior design would be an additional cost but we can handle it all in-house to make your life easier. Let’s hope, post pandemic, we can move forward with this project and create a stunning entertaining addition to this home.

So, now you understand the costs… are you ready to add a glass box, rather than a traditional conservatory? Drop us a line to get in touch and let London Contemporary add that wow factor to your home. Imagine if your kitchen looked like this…!