What you need to know about glass extensions

Apart from the obvious ‘wow’ factor that a glass box extension brings, there’s also something very glamorous about a room built (mostly) from glass. And of course it can also be used to connect two or more areas of a home instead of just serving as an extra add-on space. 

But the best thing about a glass extension has to be the views that come flooding into your home. Your garden, a stretched-out landscape, the beach and ocean, your adjoining patio… whatever lies outside becomes part of your indoor décor, as you get to relish in its beauty all day long. 

If your house is listed or located in a conservation area, Planning Permission will be required. However, most small extensions are covered under Permitted Development Rights, but remember that even this has a few rules and limitations (like the fact that your glass extension can’t be higher than your house’s roof or four metres).

Best contact your local council to get all the details before you start planning!

As you’re going to want that extension to flow from the rest of your house, it may mean compensating for the glass surfaces by increasing insulation levels elsewhere or opting for other energy-saving measures. These extra costs (like high-specification glass and structural solutions and alterations) are going to work out pricier than if you had opted for a more conventional build. 

Keep in mind that the fees can also be higher for the architect, designer and structural engineer, seeing as more work will be involved. But the final price will vary greatly depending on various factors such as the size of your glass extension, the manufacturer, the architect, etc.

The rule of thumb is to budget for a minimum of £3,000 per m².

Always consider the age of your property, the location of the structure and what you want to use the new extension for. For example, a south-facing glass extension will be privy to more sun and risks getting very hot on the inside. On the other hand, a glass extension which faces north and has underfloor heating can be quite perfect. 

If that extension is meant to increase your kitchen size, ensure that the units are positioned in the centre – placing them against a glass wall will, obviously, be impossible. 

You might use specially formulated glass in double- or triple-glazed systems, but even then more heat will get lost through the glazing than with a solid structure. When it comes to modern building regulations, high levels of thermal efficiency are required, and it can be tricky to get a completely glass extension to comply.

And don’t forget about the glare of the sun, even here in the UK! 

If it’s the cosy factor you’re worried about, consider timber framing. Similarly, pure glass walls beneath a solid roof (or even a solid roof with some openings) as opposed to one that’s made of clear glass can more easily conceal curtain tracks or blinds (for added privacy, shade or warmth) recessed into the ceiling. 

A glass box extension will usually require specialist design detailing. You and your architectural designer may come up with its layout and elevations, but it will be up to a designer, manufacturer or contractor to assist with crucial details like door systems and glazed walls. 

Of course this also depends on what you want to achieve with your glass box. One that’s constructed entirely out of glass, including the load-bearing structural glass beams and columns, is a very specialised project that is not carried out by all companies. 

A less complicated design would be a contemporary glass extension built with a more conventional structure (like a steel frame, but with floor-to-ceiling glazing and sliding doors). For this type of project, most professional residential architects and structural engineers can be right for the job, as long as they work with a glazing specialist or door supplier.

Glass might be the major element of that extension, but you still have plenty of design options to make it as unique as you want it to be. Those walls of glass will probably be placed in a frame, which you’ll likely want to be as thin and subtle as possible. Powder-coated aluminium is usually chosen where the paint colour is applied in the factory, ensuring a wide range of shades. 

Also remember that the glazing can sport different coatings to influence the look of your extension, from completely transparent to uniquely reflective. 

If you opt for a solid roof above your glass box, its supporting structural element will be a key part of the design – possibly even overhanging to protect the glass from the sun. A brise-soleil or sun shield can then be added, which will make the entire design become much more contemporary.

Let’s see how you can go about Improving a home without planning permission.