What is a glass extension?

Glass extensions are increasingly popular for several reasons – they are thermally efficient, aesthetically beautiful and flood your home with natural light.

There are lots of choices when you come to design your glass extension. A glass box extension is as it sounds; this is a frameless extension with no visible supports. Glass framing creates invisible joins between panes, or a sleek metal framework provides a stylish finish.

Other options include:

  • Glass walkways
  • Roof lights or skylights
  • Glass walls
  • Glass roofs

How much does a glass extension cost?

The cost of your glass extension will depend on lots of factors, including:

  • Where on your home this is built
  • How easy the site is to access
  • What type of glazing panels you choose
  • How large your extension is
  • Whether you need foundations

Typically, a single panel of reinforced glass will cost from £1,000. If you are looking to create a glass-framed extension, the average total build budget is from £20,000 to £80,000.

Should you be considering a more straightforward conservatory construction, these can cost as little as £3,000 and up to £20,000 for more elaborate designs. Why not use Refurbb to get a quote for extension.

How long does it take to build a glass extension?

A glass box extension can be relatively simple to build since the panes are quicker to install than manually building brickwork. You should expect the average construction time to take at least eight weeks, and usually closer to three months.

Larger or more complex designs can take closer to six months to erect.

It is worth remembering that most glass extensions will require planning permission, so you need to factor in additional time for this process. Usually, a timescale of between six and twelve months is necessary to complete an extension project from start to finish.

Why do homeowners choose glass extensions?

Glass is a modern and elegant material, and with new technologies and sturdier reinforced panels is a viable external building material.

Benefits to choosing a glass extension include:

  • Bringing a modern and contemporary feel to your property
  • Using a stylish material for your extension
  • Significant increases in natural light
  • The expansion of your home to appreciate your outside views
  • Thermal efficiency with thermal panes designed to reduce heat loss on winter

Treated glass panels prevent glare and excessive heat, so are alternatives to the traditional conservatory and are built to withstand the elements and provide comfort all year round.

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Will I need foundations for my glass extension?

Glass box extensions do not always require foundations – although more significant extensions will. Glass conversions are usually built from an aluminium framework that is bolted onto your property, as well as secure footings. There may be some groundwork needed to make sure there is a firm and stable surface to attach these fixings to.

One of the advantages to a glass extension is that they are very fast to build, and do not require any damp proofing that is necessary for a traditional brick extension.

The panes are built off-site, whether standard size or created bespoke, and then are delivered to site to be fixed to the structure.

How are glass extensions built?

Glass extensions are made to measure. When the glass panels are delivered to your home, they are ready to fit.

Therefore, many homeowners choose a glass extension over a conservatory since the precision fit nature of the panels avoids any issues with condensing water or gaps in the structure.

The ambient properties of glass with coatings to reduce glare ensures that the temperature remains stable, so glass extensions do not overheat in summer or become too cold in winter.

While a glass box extension is usually a little more expensive than a conservatory, it offers improved energy efficiency. It is a durable structure owing to the strength of the aluminium frame.

What can a glass extension be used for?

Glass extensions are more versatile than conservatories, and can be used in any number of ways:

  • As an extension to your kitchen, living space or dining area
  • As a reading room, additional sitting room or sunroom
  • As a playroom or home office
  • As a hot tub or swimming pool area

A glass extension can either be a standalone room, or an extension to an existing space where the internal walls are knocked through. This means that you could transform your kitchen by extending outwards, with an entire glass wall to enjoy the view of your garden.

How energy efficient is a glass extension?

One of the primary concerns with a glass extension is around energy efficiency. Energy usage is increasingly important given the cost of utilities and is an essential factor when selling your home.

Glass box extension plans need to demonstrate that they can meet targets for energy efficiency of the property, which is governed under building regulations. There is a common misconception that glazing is not permitted at over 25% of the total property floor area, but this is a guideline rather than a hard and fast rule.

The basis of this rule is about thermal efficiency, not percentages, so there are many ways to make sure your glass extension is compliant with building regulations without compromising on the size of your extension or the amount of glazing it incorporates:

  • Choosing e-coated glazing which is high performance
  • Avoiding cheap glass extensions and choosing triple glazing
  • Upgrading your insulation
  • Replacing your boiler with an energy-efficient model
  • Adding more loft insulation or cavity wall insulation to your home
  • Upgrading your windows elsewhere in your home with energy-efficient designs
  • Installing low heat (LED) lighting

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How do I design a frameless glass extension?

Frameless glass is a striking extension to choose, and using triple-glazed or coated glass ensures that your extension is warm and energy-efficient. This also assists in meeting building regulations.

Your glass extension can incorporate any kind of doors, depending on where in your property it is located and how you wish to use the space:

  • Slim framed sliding doors
  • Bifold door sets
  • Flush glazed hinged doors

Without visible metal framing, choosing wider doors with sliding mechanisms makes your home feel truly spacious, and avoids breaking up the line of sight.

Where can I get design inspiration for my glass extension?

Structural glass is cut and fitted to mould to your home, so it is very flexible in design. There are a number of ways to help decide what your extension should look like:

  • Consider how large your extension should be, and the best place around your property for this to be located.
  • Think about what you want to use the room for, and therefore what sort of utilities and doors it will need.
  • Take a look at the roofing options available and how this can fit in alongside your existing home.
  • Have a walk around your home to consider what outdoor spaces you don’t use, and to decide how much garden space you are happy to sacrifice in order to create your extension.

Glass extensions by their nature have much slimmer walls than a traditional brick-built extension, so one advantage is that you will enjoy a larger footprint without as much capacity taken up by the external walls, insulation and plasterwork.

If you are working with an architect, they will be able to help with advice and suggestions about the best design options for your property and your budget.

You can also have a look at other glass extensions – either in your area, or built onto similar period properties – for ideas about how these have been made, and what sort of designs you like!

If a glass extension is too costly and you have a garage why not find out more about the cost of garage extensions.

Glass is a modern and elegant material, and with new technologies and sturdier reinforced panels is a viable external building material.

Frequently asked questions

How is a glass extension different from a conservatory?

A conservatory is a similar construction to a glass extension since both are mainly glazed, bring in lots of natural light and connect your garden to your interior.

However, most conservatories are constructed from brick, usually featured dwarf walls that come up to waist height with the remainder glazed.

A glass extension offers floor to ceiling glazing and can be designed and built in any shape or construction. This flexibility makes a glass extension more versatile, rather than a standard shaped conservatory.

Do I need planning permission for a glass extension?

Whether you need planning permission depends on a lot of factors. Some extensions can be erected through permitted development, which means that you do not need to apply for planning permission.

However, your extension will need to comply with building regulations so you will need to factor in this time.

In order to be built under permitted development, your glass extension:

  • Most not extend outwards from the front of your property past your existing home
  • Must be no taller than 3 metres if within 2 metres of the property bounders, or 4 metres if outside of this proximity
  • For a rear glass extension, the conversion cannot be more than 3 metres deep for semi-detected and terraced homes, and 4 metres deep for detached properties

If you are in any doubt as to whether you need planning permission, it is always wise to contact your local planning authority.

What sort of builder do I need for a glass extension?

Conservatories are a simple build and can be constructed by general builders or conservatory companies. A glass extension is more specialist and usually designed by an architect.

The precision nature of the manufacture of the panels means that they are made to measure. Specific equipment is needed to transport and lift each panel to instal them, so this is not something a general builder would be able to provide.

Ideally, the fitting and manufacture of the frame and panels are carried out by the same contractor, or by tradespeople working together. Sometimes this is managed bu your architect who will oversee the design and build process from start to finish.

The contractor fitting the panels will need to understand the framework, particularly if you choose a glass frame, to ensure that the fitting is accurate.

How else can I use structural glass in my extension?

If you aren’t sure about a complete glass extension, there are lots of ways to incorporate this contemporary material into your extension.

Glass walkways are a unique focal point and are often used as a roof light for a basement extension. This has multiple benefits:

  • Bringing in more light to the basement extension
  • Providing a focal point for the walkway above
  • Easy flat installation to maintain a smooth walking space
  • Aesthetically pleasing toughened structural glass

Skylights or roof lights are a simple way to include more glass in your extension. They bring in natural light to areas that do not have many windows, are in a darker position in your home or are located at a side return that does not experience sunlight during the day.

Glass walls are another contemporary design, and similarly to a full glass extension are a complete sheer panel of glass that provides a spacious feeling.

Another option is to consider a glass roof. These are made from the same structural glass to withstand the elements, and add a different dimension to the room. This type of roof is energy-efficient, cheaper and easier to maintain than a flat roof, and provides access to natural sunlight during the day and the night stars in the evening.

What is over-glazing in glass extensions?

A term you might hear when planning your glass extension is over-glazing. This phrase means that the extension has too much glass and does not meet the building regulations for energy efficiency.

In a nutshell, homes must have a minimum energy-efficiency rating of C. The guidelines state that an area equivalent to no more than 25% of the floor area of the property should be glazed, because constructions such as cavity walls are more thermally efficient than glazing.

However, if you choose to upgrade your glazing, improve the energy efficiency of your home elsewhere (for example with an efficient modern boiler, LED lighting or triple glazed windows), you can still meet the minimum requirements with a fully glazed extension.

Rich Crossley
Having spent 30 years working all over the world for top-tier investment banks, I’ve owned and developed houses all over the world – Europe, the US and Asia. I’m now based back in the UK and involved in the property industry – oh, and I’m a keen DIY enthusiast!
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