Glass Extensions: Planning And Designing Your Own

Concrete house glass extension

When most people think of a glass extension they immediately picture a conservatory. Although these are a lovely addition, they tend to become incredibly hot in the summer and too cold to use in the winter. This means they become a dumping ground for storage or worse, wasted space.

A glass box extension is the modern version of a conservatory. They look fantastic, are heated just like a normal extension, and are valuable extra space you’ll get use of all year round. If you’re thinking about building an extension in London, let’s take a look at why you should seriously consider a glass box over a conservatory or conventional addition. 

How Much Does a Glass Room Extension Cost?

The average cost of a medium-sized glass extension in the UK is between £24,000 and £37,500. When it comes to London, that price can go up to £72,000 or more depending on the size and quality of the build.

If you’re thinking of having a traditional roof and just glass walls, you might be wondering what do glass walls cost? They will set you back around £2000 per metre squared. 

Building Regulations for a Glass Extension

Most small to medium-sized glass extensions tend to be covered by UK Permitted Development Rights. However, it’s always best to contact your local planning authority in London to check if there are any restrictions. This is especially important if you live in a conservation or heritage area. 

A large-scale glass box building may be subject to Part L limits on construction. This limits the number of glazed elements or openings to 25% of the floor area. These limitations help to reduce heat loss and increase energy efficiency. 

Glass roof seen from the inside of a house

Large glass extensions are known as “over-glazed” and your design plans may be rejected by planning authorities if they fail to meet regulations. 

When working with an extension contractor, they’ll ensure your glass box is compliant so your project isn’t stalled.

How to Make a Glass Box Extension

There are many stages of a glass extension. Here is a rough timeline of what you can expect:

Week 1: Hire a contractor

Your contractor will oversee the project, organise materials, order glazing, and give input on aspects of the design. 

Your contractor should be familiar with the build of glazed extensions and have connections with a glazing specialist who can provide the materials for your project. They’ll also be able to advise you on how you can save money on your extension

Week 1-6: Hire an architect & get planning permission

No matter how well you think you can design this yourself, it’s always best to hire a professional architect to draw up plans for your glass box building. They will address any issues with your designs, make use of every inch of available space, and ensure the structure is sound.

Hiring an architect will also help your plans get accepted by planning authorities much more quickly. But it can still take around 8 weeks to get planning permission in London. 

Glass extension near pool

Week 9: Building the framework

Once planning permission has been granted, your build team will begin with the framework. The “box” needs to be connected to your exterior walls. If you’ve opted for a frameless design, this frame will be hidden in the building finishes as much as possible to give a seamless look. 

Week 10: Installing the roof & walls

Depending on the size, the roof may be one solid piece of glass or may be broken up into sections to reinforce the structure. 

When it comes to how to build glass walls, they are fixed in place using a high-grade silicone sealant. These glass panels are incredibly heavy, so this is a slow, steady process.

Glass Extensions to Inspire Your Project

If you need of some ideas for your glass extension, here is some inspiration:

Glass extension with high ceiling

The timber framing used here gives a more rustic vibe. If you love the idea of incorporating wood into your glass sunroom, this is a great way to do it.

Modern glass extension

This one is much more modern. The pitched roof not only looks great but also gives additional ceiling height inside the property. And the anthracite framing is a popular finish. 

Classic style glass extension

This conservatory-style glass sunroom floods the room with light, making it the perfect spot for a dining table. And the tall french doors give the room connection to the garden.

You can just about make out the scale of this glazed structure in the reflection of the glass. The sloped roof and square pattern of the glass make this ultra-modern yet industrial. The thin grey framing looks great and is a nice idea if you don’t want a frameless extension. 

Love the idea of a glass extension on your home?

Glass extensions make for a lovely addition to any house. Reach out to us today and let’s plan and build a room flooded with natural light.

Leave a Comment