Design Options for Structural Glass Roofs

Brook Bar: Large glass roof to country house renovation

Flat structural glass roofs and rooflights are a popular and timeless element to modern architectural designs. The bespoke nature of these frameless installations means that glass roofs can in any number of shapes, sizes and designs.

Structural glass roofs and roof lights are designed with no integral frame; instead, they are supported using structural angles enabling designers to seamlessly integrate these roof windows into any building construction minimally.

The overall look and feel of a structural glass roof will be determined mostly by its size and length of glass joints within the glass roof design.

Frameless Rooflights

For smaller roof installations a single pane of glass may suffice. These singular glass roofs are often known as ‘roof lights’ and offer a frameless window through a solid roof structure. The structural pane of glass will be installed onto a solid upstand that is created by the builder.

Whereas in the past these rooflights would be created using simple steel or aluminium angles are to fix the piece of frameless glass into the building we can now offer the new thermally broken rooflight system from Sieger Systems. This new rooflight solution uses a unique thermally broken angle to support and fix the glass rooflight into the upstand. The use of a thermally broken connection increases the thermal performance of the rooflight and eliminates the cold bridging effect that is apparent with standard rooflight details.

This new solution for frameless rooflights offers architects and specifiers improved thermal performance whilst maintaining the frameless design of a standard rooflight. These rooflights are often finished with a back painted band around the edge of the rooflight which is visible externally. This area of the opaque glass around the external edge hides all the structural fixings and offers a neat external view to the roof glazing.

The below roof light was installed onto a new rear extension to a home in London. The roof of the extension was overlooked by the upper bedrooms so it was important that it looked visually appealing. You can clearly see the stepped edge of the structural glass pane which is back painted, hiding all fixings and silicone neatly.

three frameless rooflights
Hazewell Road: Above the casement sliding folding door openings lie three frameless rooflights

Internally these rooflights can be finished frameless as you can see from this large rooflight installation to a home in London. The large rooflight was positioned at the top of a multi-floor staircase and bathed the stairwell in natural light throughout the day.

large frameless rooflight over the stairwell.
Edis Street: large frameless rooflight over the stairwell.

The Sieger Rooflight System is only suitable for single panes of glass. If you want a larger rooflight or are including multiple panes of glass into the roof design then a supported glass roof or strip light would be the better solution.

Supported Glass Roofs

As structural glass installations do not use a frame any multiple glass units are sealed and connected together using structural silicone joints. When a silicone joint is used in a glass roof it will need supporting if it is over 1.3m in length.

There are various ways in which you can support a structural glass roof installation. The method you ultimately choose will depend on the internal design of the space as well as the budget.

A Glass Beam supported Glass Roof

glass beams to side infill extension roof
Onslow Avenue: glass beams to side infill extension roof

Glass beams can be used to support large glass roofs maintaining a clear, all-glass design. The clear and frameless nature of a glass beam design creates a completely frameless glass roof design maximising the amount of light that comes through and offering unbroken views out.

When specifying a structural glass beam for your roof Low Iron Glass is always recommended. This is because natural clear glass has a green tint to it. When layered in thick units (like those used in a glass beam) this can create a strong green tint to the glass structure. Low Iron Glass will give you a much clearer overall finish to the glass pane which can be layered multiple times whilst maintaining clarity.

The glass beams sit below the glass joints on glass roofs with larger spans and support these structural joints along their length.

The below basement renovation and extension in London used structural glass beams to support the glass roof which covered the entire extension. The left-hand side fixing of the glass beam was completely hidden by the building finishes with only a minimal stainless steel fixing on show to support the beam on the right.

Prebend Street basement extension by Guttfield Architects.

A Steel Section supported Glass Roof

Similar to glass beams, a steel section can be used to support the underside of a larger glass roof creating a different internal design. The steel section can be powder coated to suit your design but is generally a dark grey or black colour to match the structural silicone and spacer bars of the insulated glass unit.

Steel supports to a structural glass roof creates a minimal supporting frame. The resulting glass roof design is very in keeping with loft style projects or industrial design schemes.

This steel framed glass extension in Buckinghamshire utilised steel sections to support the glass roof. This supporting method was perfect for this extension design as an industrial design was desired. Thermally broken steel doors were used as the rear access doors to the garden and the steel supporting structure for the glass helped to maintain that design aesthetic.

Rowood Farmhouse: An industrial house extension using steel framed doors.

Other Supporting Options

Although glass beams and steel sections are the most popular ways to support a structural glass roof there are plenty of other ways and materials that can be used. It will really depend on the design of your building as to what is best.

If you are using timber or composite windows and doors why not use Timber beams to support the glass roof. For a metallic finish in a unique design why not opt for a Stainless Steel T section or box below the glass roof?

Strip Rooflights

Where roofs are slimmer (with glass joints under 1.3m) then the structural glass roof will be silicone jointed together as normal but no other visible support is necessarily needed. The resulting glass roof design just contains horizontal black lines where the glass units meet.

These structural glass roofs tend to be referred to as ‘strip rooflights’ as they are in line and thin, creating a ‘strip’ of natural light through a space.

A strip rooflight can be used to great effect over a hallway or staircase like the below new build home in Exmouth. The house was designed by Stan Bolt Architects and utilised many clever punches of structural glass throughout the building.

a strip rooflight over the staircase on this modern new build house.
Exmouth: a strip rooflight over the staircase on this modern new build house.

Another popular use of a strip rooflight is at the connection between a new extension and the existing building. The below residential extension used a thin structural glass rooflight to mark the division between the new and old space. This strip of glass in the roof also helps bring natural light further back into the building.

Totteridge Lane: strip rooflight to the rear extension

 

Eaves Windows

These structural glass installations are used to create ‘up and over’ glass elements that form part of the wall and then continue upwards, following the line of the roof. In most cases you get a simple glass to glass connection between the vertical glass and roof glazing. All external angles and fixings can be hidden by the building finishes which creates a frameless glass design.

Eaves rooflight designs are well suited to projects that have a sloping roof. The ‘slots’ of glass can create an impressive visual as it appears that slithers of the building have been cut away, bringing in light and allowing a snapshot of the outside. If you don’t have a good view outside you could use translucent glass to the bottom vertical pane of glass. This will maintain light coming in but block unsightly views.

frameless glass eaves window to house extension

 Further Reading

If you would like to find out more about the roof glazing options shown here just visit the IQ Glass website where you will find more technical information and image examples.

Structural Glass Rooflight Designs

The Sieger Thermally Broken Rooflight System

Structural Glass Roofs

Strip Rooflights

Eaves Windows

Safety of your Roof Glazing 

Solar Control Options for Structural Glazing 

Structural Glass & Glazing – What is it? 

See all of these glass roof solutions at the IQ Glass showroom in Amersham. View our 3D Virtual Tour below.

 

 

 

 

 

 

 

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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.