How To Plan Your Glass Box Extension Like A Pro
Thinking About Getting A Glass Box Extension? ...Read this first


By Slimline on 19 April 2019
Posted in Property

Glass box extensions are an increasingly popular way to create more living space. Find out what you need to know to make your extension a success.

How To Plan Your Glass Box Extension Like A Pro
Thinking About Getting A Glass Box Extension? ...Read This First

Everywhere you look you will spot a traditional conservatory jutting from several properties along your street.

But there’s a new kid on the block, who is slowly taking over the town.

This new boy takes the form of a glass box extension, and he’s bold, bright and becoming more and more popular.

But why are glass box extensions becoming the new choice of outdoor room, and how exactly do they differ from conservatories?

If you are thinking about getting a glass box extension, but are confused as to exactly what they are, we’ve got it covered. Read on to find out why this particular new kid looks here to stay...

What is a Glass Box Extension?

Not to be confused with a conservatory, a glass box extension uses glass sides and a roof to create extra space in your home and can be thought of more as a glass outdoor room. They tend to be glazed with full glass panes to provide uninterrupted views and are built on a slim aluminium frame system to give a minimalist appearance. The strength of aluminium allows large, thin panes to be supported safely.

The doors are often bi-folding or sliding, again constructed from glass to maintain the uninhibited views to the outside, while allowing the area to be fully open to the outside when weather permits.

These extensions are seen as futuristic and modern and come in many guises and designs, but they also make a perfect match for traditional properties, acting as an anchor between old and new.

You can see examples of our glass box and structural glass extension solutions here.

What's the Difference Between a Conservatory and a Glass Box Extension?

Similarities, of course, exist between a conservatory and a glass box extension. Both provide extra living space to your home and are a central point between internal and external living. They afford plenty of natural light and extensive views to the outside while protecting inhabitants from the weather.

However, that is where the similarities end. Unlike a conservatory, they do not have any brickwork such as a low (dwarf) walls; instead, the glass extends from floor to ceiling, providing a transparent outlook into the outside world, and an illusion of a seamless connection.

Aesthetically, they differ from conservatories in many ways. Conservatories tend to have a traditional look to them which makes them easily recognisable, whereas glass box extensions can be designed to fit your home and space in many different facets, shapes and sizes.

The design and build process for glass boxes follows a made-to-measure technique which results in a precision product and an efficient and quick installation process. Conservatories can be more challenging to build; common issues include condensed water and problems achieving the required tightness gaps, which are not common with glass box extensions.

Conservatories also have temperature issues, fluctuating between hot and cold, dependent on the outside temperature. Glass box extensions tend to have a more ambient temperature due to the thermal properties and coatings nature of the glazing glass used.

Glass box extensions are not as expensive as you might think, but do tend to cost more than conservatories. However, this is reflective of the unique designs and the quality and strength of the aluminium frames. Maintenance is low, and longevity is high, resulting in a product that will last for many years with very little upkeep required.

Do You Need Planning Permission for a Glass Box Extension?

As it is an extension to the property, a glass box will need to comply with building regulations but it if meets certain criteria it won’t need planning permission. These include:

The extension does not protrude at the front of the property

The extension sits within 2 metres of the boundary of the property, the eaves must be less than 3m high, or 4m if further away from the border

For extensions at the back of detached properties, it cannot be more than 4m in depth. For semi-detached or terraced properties, it is limited to 3m

The width of side extensions must not be more than half the width of the building.

However, if in any doubt, contact your local authority for advice.

Do You Need Foundations for a Glass Extension?

Foundations are not normally required for a glass box extension, nor is damp proofing or other work that extensions usually necessitate. The aluminium framework is bolted to the existing property and to the ground so it will require a firm surface - but deep traditional footings are not required. They usually only take a few days to fully install, as they are manufactured off the property and designed to fit neatly to the existing structure when on-site. This affords a more flexible approach to location and reduces the time, cost and mess associated with traditional building techniques.

Multiple Functionalities

A glass box extension is more than just a "sunroom". It’s a versatile and functional space that can be used in many different ways. They open up any room and allow natural light to flood through into the darkest corners while transforming it with extensive panoramic views that are normally hidden behind brick walls.

Because of the flexibility they offer to designers and architects, they glass box extensions can be are typically favoured utilised to when joining existing aspects sections of your property, or extend your kitchen or living area. Think break- out or relaxation area, or a place to socialise and party. They can even house your hot tub or swimming pool!

Who Can Build a Glass Extension?

Unlike some conservatories, which can be built by general builders, glass box extensions require an experienced specialist to construct them. They are often architecturally designed and large panes of glass are made to measure. These take careful handling and specialist lifting machinery, and an understanding of fitting of the framework is also a necessary requirement for anyone undertaking a glass box buildboxthis build.

Thermal Efficiency is a Must

To comply with building regulations, glass box extensions must demonstrate they meet Part L of the planning regulations, which outlines targets for the energy efficiency of the building envelope. This limits the total amount of glazing within the building to 25% of the total floor area.

Glass box extensions can easily go over this allowance. However, it is possible to  negate this problemget around this by using high-performance low e-coated glazing ss to help lower the u-value. This will then allow you to install more glazing, as building regulations are only concerned with the total u value of the property.

Quality glass extensions usually meet these specifications, whereas cheap glass extension will result in heat retention in summer (solar gain) and heat loss in winter, and are less likely to be approved by building regulations.

What other kinds of structural glass extensions are there?

If you are not in a position to install a full glass box extension but love the idea of creating more light in your home, consider these alternatives.

Glass Roofs

Rooms that lack in light can benefit from structural glass in roofing areas, as well as affording a pleasing visage. If planning restricts the installation of new windows, glass roofs can add a new dimension to your room. With new advancements in glass properties, glass roofs can now help stabilise the temperature, regardless of external conditions. Surprisingly, they are an energy efficient choice, as well as being lower in maintenance than other types of roof, including flat roofs.

And who doesn’t love the sound of pattering rain on a glass roof, while sitting warm and cosy inside!

Glass Walls

There’s something special about glass walls, unharboured by frames or brick. Aesthetically appealing, they open up any area and bring the outside in, while still protecting you from the elements via a transparent barrier. Create a feeling of space or open up north facing, dark rooms; or bring warmth to large cold rooms. , or tTransform a bathroom into a place where you can lounge in the bath and enjoy the vista.


Perhaps a glass wall or roof is not an option, but with a roof or skylight, you can still bring natural light into much-needed areas - just on a smaller scale. Contemporary designs work well on both modern and traditional properties while providing extra ventilation and light whenwhere needed.

Walk on Glass

In city centres where space is at a premium, many people are looking at basement conversions to create extra living areas. Walk on glass rooflights are designed for flat installation, perfect for basement ceilings that extend into garden areas, or sunk into a patio or decking or incorporated into the floor between two levels within your property. Specially toughened glass is designed for structural safety while offering an aesthetic option for lighting up otherwise dark, inaccessible areas.

So in Summary...

The benefits of glass box extensions are numerous. They are not limited to one type of property but suit all sorts and sizes, from modern build to traditional cottage. Designs are flexible; don’t just think square box on the side of your property as they can be planned to fit any aspect or area.

Strength and durability come as standard, and low maintenance gives you more time to sit and enjoy your new extension instead of painting and repairing.

Large panes and subtle frames allow for expansive, uninterrupted views that allow the outside in, without the side effects of coping with the unpredictable British weather. Let natural light flood into any area of your property, while adding extra footage for a multitude of uses.

Compared to conservatories, glass box extensions provide an attractive alternative and uniquelyuniquly customised e space that focuses more on bringing the outside in.

There is always a place for the traditional extension -, but don’t dismiss the new kid. They’reHe’s full of surprises that will make you wonder how you ever managed without your new glass box extension.

We’d love to discuss your structural glass extension requirement and give you a few options. Please feel free to give us a call, drop us an email or pop in to our showroom in Surbiton, Surrey for a chat.

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