Useful Information about Architectural Glazing

A guide on how to maximise full height glass extensions

A full height glazed extension to London dwelling with the front elevation roof being taller than the side connected to the building.

Taking the complexity out of complex full height glass extensions to maximise height and light. 

How can you maximise the height of a structural glass extension to create a full height glass extension? Read our guide for some insight in to how you can design a glass box extension to make the most of height and space.  

Glass extensions are a popular way to extend properties, offering a clear and minimal way to add space and more natural light to any type of property. But when it comes to designing a full height glass extension there are various ways you can maximise the impact of these all-glass designs.  

The team at IQ, are experts in the design and creation of structural glass extensions. For the best advice, contact the team with your proposed designs and we can assist in ensuring that the new glass space offers the best design and performance.  

Read on below for some of our top tips to create a full height glass extension.  


What is the typical height of a full height glass extension 

Structural glass extensions are bespoke so they can be designed to any height required of the architectural brief. Double height glass extensions are popular as well as glass extensions that encompass mezzanine floors.  

When it comes to the height of an extension, it is ideal to maximise this to create a full height glass extension design. If you are creating a full height glass extension to an existing property, there may be existing structural limitations on the height of the glass extension such as existing ceiling heights or first floor windows.  


Double height frameless structural glass in Kew Road extension.


How can I maximise the height of a glass extension 

When working within an existing building structure, you want to ensure that the height of the full height glass extension is maximised.  

Very often, we will see glass extension designs with the glass roof pitched away from the existing building towards the glass doors of the glass extension. Typically, the point where the glass roof of the extension connects with the existing building is predetermined due to existing ceiling heights, existing supporting steels or the location of upper floor windows. The glass roof then falls away from the building until it meets the glass doors or furthest glass elevation.  

This is a logical approach however, internally, when looking out to the extension, the front end of the glass extension will naturally be slightly lower to facilitate the fall of the glass roof.  

Creating a glass extension this way can make the garden doors within the glazed extension short or smaller than you would prefer.  

However, the simple change in the direction of the glass roof fall can have a massive difference on the feeling of space and height in the glass extension.  

Taking the above example where the glass roof must connect to the existing building at a specific location; if you angle the glass roof back towards the building (instead of away) then the glass extension gets taller as it spans away from the existing structure. The highest point of the glass extension will then be the front elevation or the glass doors. The glass wall or glass doors of the extension can then be full height, maximising views, and space at this important elevation.  

Where the glass roof then meets the wall, IQ can use a discreet structural gutter to both support the glass roof and collect any water run-off. This structure can be hidden by the building finishes so it is not visible.  


Illustration of both variations of glass roof drainage


Inset illustration of both variations of structural glass roof drainageThe left shows a typical drainage solution where the roof angle drops towards the front of the glass extension and dissipation falls to the front of the glass extensionThe right shows the opposite where the front elevation of the glass extension is taller than the connected side of the extension to the building where a structural gutter meets the wall and forms an intrinsic part of the building supporting the glass roof while acting as a gutter. 

Below examples of glass extensions with drainage channels at the front of the roof. 

Typical height glass box extension

Examples of drainage at the front of a glass extension.

Bifolding doors to rear extension with roof drainage to the front of the glass box extension.


Even though this is a small change in the approach to a glass extension design, the results offer a far cleaner finish to the glass elevations with all drainage hidden away. The height of the glass extension at its critical location is maximised whilst not interfering with any existing structures or changing the footprint of the extension in anyway.  

The ‘hidden benefits’ include a minimal design to the front of the glass extension.  From the outside and inside perspective, there are no visible downpipes and guttering that appears to ‘teeter' over the edge of the glass extension. 

When maximising the roof height of the front elevation, from an internal perspective, looking out, the sense of space and height increases significantly creating an airy and inviting ambiance with enhanced views of the outdoors. 

A full height glass extension with taller glass at the front compared to the adjoining building height of extension.

Double height structural glass extension increases the space and light within the property


Creating a Double Height Glass Extension  

When creating a double height glass extension to increase useable space, natural light and to deliver the ultimate visual impact, combining structural glass with minimal framed oversized sliding glass doors can achieve the ultimate double height glass extension with seamless connection to the gardens.  

Double height glass extensions are growing in popularity, particularly where expansion in footprint is limited. Gaining space through double height structural glass for atriums or ultra slims double height sliding glass doors enhances a sense of internal space while maximising the amount of natural light into the deepest and most narrow of properties. Typically, London period properties have limited space, and in order for architects to reconfigure the layouts, the addition of double height rear extensions and side return extensions into redundant living space is a clever way to reclaim dead space.  

Contemporary full height glass extension designs with sliding doors facilitate the connection between the building and garden.  However, by creating a double height glass extension, it then allows the architects to use the structural glazing to highlight other key features such as a beautiful spiral staircase or sculpture while adding drama to the building.    

Double height glass extensions can create the most stunning entrance spaces where the original layouts were reconfigured to match the requirements of modern day living and enhance flexible space for entertaining family and friends.  

A fine example of a double height glass extension to maximise space is our Gloucester Walk project where clever design turned redundant space into a bright double height glass extension. The IQ team worked with architects,  ATELIERwest on this prestigious Kensington terrace renovation using full height structural glazing for maximum visual impact and vastly improved space. A side glass glass infill with double height glass doors formed part of this eye catching  ‘up and over’ extension.  

The double height glass doors stand at 5.7m tall and meet with the double height glass roof. The IQ team designed all the steel beam elements connecting the double height glass doors via the steel roof.  Despite the weight of the double height slim framed sliding glass doors with 20mm slim profiles, the precision engineered sliding mechanism within this high performance system can be opened manually with little effort.   

The first floor piano room benefits from the light that the double height glass extension provides with views out to the garden .   

The result being a cohesive and light filled design.  

Double height glass extension at Gloucester Walk.

Gloucester Walk Double height sliding glass doors

Double height glass to London property


Another narrow multi-storey London Mew property, Grosvenor Crescent, created a double height glass extension designed with a 2/3 storey void allowing natural light to flood through all floors of the dwelling. A structural glass rooftop extension provides much need space for its occupants to enjoy all year round. The existing first floor windows in this double height glass extension were integrated to create the double height aspect which provided much need light and fantastic views of the cityscape.  


Double height glass roof to multi storey Mews property integrating existing windows with new glazed structural addition to achieve a double-height aspect with views out to the City.


If my Glass box extension is south facing, is it a bad decision to want to increase the height of the front of the extension? 

At IQ Glass, we offer structural glass and glazing solutions to suit the demands of the building’s performance, Building Regulations, orientation and location.  

A south facing full height structural glass box extension with sliding glass doors of high performance low e-thermal coated glazing and solar control ensures that the occupants can enjoy the space in the warmer months as well as the winter months.  

With IQ’s innovative glass, there is no ‘trade -off’ in the desired outcome. Many of the most prominent and highly regarded architectural practices from all over the world work with us   

Are you looking to incorporate a full height glass extension?  Contact our technical team today!  


Further reading 

A beginners guide to glass box extensions

6 Examples of Double Height Glass to Narrow London Properties 

Glass in listed buildings

Glazing for double-height windows

Architectural glazing, wind resistance and wind loading 

How to use structural glass and slim framed sliding glass doors together