What You Need to Know About Glass to Glass Connections

Side Infill Extension with Glass to Glass Connection - IQ Glass

How Do you Create Minimally Framed Glass to Glass Connections?

What is a ‘Glass to Glass Connection’?

A glass to glass connection is an architectural and construction term that is used to refer to any connection between two elements of glass, meeting on a corner or angle, with no frame in between.

Glass to glass connections are used to create a wide range of architectural glazing installations including glass box extensions, glass links, oriel windows and eaves windows.

Due to the lack of frame, a glass to glass connection creates a very minimal finish to a glass structure and is most commonly seen on modern architectural design projects.

Glass Box Extension - IQ Glass
Camberwell – Glass Box Extension

How Does It Work?

The process of creating a strong and weather resistant glass to glass connection is highly technical and you should always utilise the services of a highly experienced architectural glazier to complete these types of structures.

Black structural silicone is used to join the panels of glass together at the corner. Generally, any overlapping glass will be back painted black to create a sleek and minimal connection, hiding any messy silicone and the black warm edge spacer bars that are placed between the double or triple glazed units.

In the case of glass to glass connections between vertical and horizontal glass, the vertical pane is usually slightly thicker to allow for the extra weight the glass unit will be bearing. In some cases, a strengthening glass interlayer might be used to increase the strength of that supporting glass unit even further. However, you must not confuse this additional strength within the glass units for structural glass i.e. glass that is put in lieu of supporting structure of a house. All it means is that the roof or horizontal glass can be loaded onto the glass below as it has been designed to take this additional weight.

frameless glass eaves window to house extension
‘Slot’ eaves windows to a modern extension project.

Glass Links

Glass links are often used to create a frameless link between two areas and are perfect for use on heritage or listed properties where a clean line between new and old is required. A glass to glass connection between the roof glazing and frameless glass walls will help to create a minimal, frameless solution suited to even the most delicate of buildings.

Glass links can be made with single, double or triple glazing depending on the thermal efficiency required. Opening elements can be integrated to provide movement between the spaces however additional steel supports may be required.

All building connections, joints and fixings, including the glass to glass connections, will need to be designed individually for each project to create a sleek glass installation.

 a structural glass link between two buildings
The Stables I a structural glass link between two buildings

This frameless glass link in Wiltshire is a great example of a glass link using a glass to glass connection. The glass link merges the old with the new between the traditional cottage and the homeowner’s new conservatory.

Here the vertical glass window and the returning glass roof of the glass links meet together with no frame, just a glass to glass connection.

The frameless nature of the glass link allows the beautiful brick home to be visible through the glass with no obstruction. The lack of frame also allows the maximum amount of natural light to pass into the new conservatory space and creates the illusion of a merge between the internal and external living spaces.

Green Barn Glass Link - IQ Glass
Green Barn – Glass Link

Structural Glass Roofs

Frameless glass roofs are commonly used in spaces where there is a lack of window space or places where more natural light is wanted. A simple flat glass roof wouldn’t require a glass to glass connection but more complicated glass roof structure might.

Any multiple glass units within a glass roof will be connected together using structural silicone. If this silicone joint is very long (normally over 1.2m) then internal structural supports will be required whether this is frameless glass beams or steel supports.

Where the glass roof has a 3D shape or is more complicated in its design, multiple glass to glass connections will be required anywhere that two pieces of glass meet. A good example of this would be a frameless lantern roof light or a boxed roof light adding height and light to a space.

3D boxed rooflight
3D boxed rooflight on Crouch Hall Road

At the Vineyard, a 3D structural glass roof was used as part of the contemporary extension being built onto the rear of the home in Richmond, London. The structural glass roof was installed to provide natural light into the property whilst also providing beautiful sky views from the new living area.

Due to neighbouring properties and ‘right to light’ requirements the party wall to the side of the extension couldn’t be any higher. The 3D glass roof structure lifted the roofline of the side infill extension whilst maintaining light to the extension and neighbours. A glass to glass connection was used between the vertical side of the roof light and the horizontal returning panes to ensure this roof light was as minimal as possible with a clean modern finish.

3D Structural Glass Roof - IQ Glass
The Vineyard – 3D Structural Glass Roof

Oriel Windows

Oriel windows are another stunning architectural glazing element that uses a glass to glass connection. An oriel window sometimes referred to as a 3D window, is perfect for creating a fully glazed window seat within the home. This style of the window provides an interesting design to your property whilst creating a bright relaxation space.

By using frameless structural glazing to create an oriel window and connecting the glass together with high specification structural silicone no framing is required.  The resulting window design is minimal, sleek and frameless; perfect for modern architectural design projects.

The 3D window at Thornton Road in Richmond is a good example of a very large Oriel style window. The large frameless window design allows natural light to pass through into the rear extension as well as providing stunning views of their external living spaces.

There is multiple glass to glass connections here with the vertical glass meeting the glass roof and the glass windows meeting at the corner. You can see the minimal back painted bands on each edge of the frameless glass panes which hides the structural silicone and spacer bar edges.

Oriel Window - IQ Glass
Thornton Road – Oriel Window

Eaves Windows

An Eaves Window is a 3D structural glass element that integrates a vertical pane of glass with a returning glass roof, often following the eaves line of the roof, hence the name.

Where the vertical pane of glass and glass roof meet you can create a completely frameless junction using a glass to glass connection. Often the roof glazing is stepped over the edge of the vertical window to create a slight lip for water to run off. High specification structural silicone and strategic use of black painted glass will provide you with a minimal joint between the two planes of a building.

Specialised strengthening interlayers are normally used within the vertical glass, allowing the glazed panels to carry the load of the above glass unit, creating a glass boxed roof light with no visible supports of the frame. The only sightline on view is where the glass unit meets at the horizontal connection, showing the spacer bars and a slim structural silicone seal. This silicone seal provides weather sealing and an adhering for the glass to glass connection.

Frameless Eaves Window
Frameless Eaves Window on Kew Road

If there is only a slight slope for this glass to glass connection then a drip off ledge can be designed into the glazing to reduce water marks and pooling. A specialised structural gutter can be utilised if the slope is directed back towards the connected building. This will connect the Eaves Window to your building and support the building edge of this structural glass roof light.

Multiple glass panels can be assembled to create longer Eaves Windows. More often than not, if the windows are smaller than 1.3m wide, no visible supports are necessary. However, if the width is over 1.5m then it is recommended to integrate either slim steel supports or glass beams to support the structural glass assembly.

An Eaves Window was created in this new build home in Barnet. Structural glazing was combined a partly glazed wall and a structural glass roof. The frameless structural glass used for our High Acres Barnet project creates a completely glazed corner to the roof of the building. This Eaves Window allows natural light to pass through the space and into the hallway, to keep it naturally lit throughout the day.

The only visible sight line for this Eaves Window is the slim black silicone seal used to adhere the glass to glass connection.

Eaves Window - IQ Glass
High Acres Barnet – Eaves Window

Glass to glass connections is an important part of frameless structural glass design. They help architectural projects to create minimal designs to the glass elements and facilitate the passage of natural light and energy. These areas of architectural glazing are complex and installations should be carried out by highly experienced architectural glaziers.

For more information on any of the architectural glazing products or projects mentioned or to speak to a professional about your project and requirements, please contact us. Visit our Contact Us page for all the ways you can get in touch.

Contact IQ Glass 

The following two tabs change content below.
Rebecca is Head of Marketing at the IQ Group and has worked in glazing specification for many years. She has a broad range of technical knowledge about all our glazing products and offers technical advice and guidance to architects for specification. Her easy to digest technical advice is often quoted in magazines and publications. You might also recognise her as one of the IQ Glass CPD presenters.