October 17, 2017
What To Consider When Specifying Structural Glass
Written by Rebecca Clayton
October 17, 2017
Written by Rebecca Clayton
The design and installation of structural glazing is not a simple process. Each installation has to be painstakingly detailed and designed. The glazing company you choose should have an in-house design team that will detail every glass fixture and junction for you – this is imperative! Below are some additional key points of consideration when looking to include structural glass on your project.
The thermal performance of a glass unit is denoted by a Ug value. This is the ‘centre pane’ thermal performance of a glass panel. You should not be using insulating glass with a Ug value of less than 1.2 W/m2K. Typically most modern double glazed units would have a Ug value of 1.1 or better but you should check with your glazing supplier what the actual Ug value for your glass specification is for each project.
A pop out structural glass window to a kitchen extension.
An advantage of structural glazing, thanks to the removal of a framing system from the glass elevation, is that there is no restriction or limit to the glass thickness you can use. This means that structural glazing is the perfect application for very deep and highly insulating triple glazing for higher levels of thermal performance.
As structural glazing is entirely frameless you do not have to consider a Uf value when calculating the overall Uw value for a glass installation.
Read More: What is a U Value?
Each glass unit will have a specific acoustic insulation value. This is denoted by an Rw value. Acoustic calculations and specifications for glass can be very complex. We go into this process in a little more depth here: Sound Proof with Glass.
Specifying acoustic reduction glazing is actually a little easier in a structural glass installation as you don’t have any set glass unit depths from the framing system. This means that you can use whatever thickness, specification and layering of glazing that is required to get the Rw value to the glass that you need.
A structural glass box extension to a central London coffee shop.
Does your structural glass installation need a fire rating? If so then you need to be very precise in your specification. You will need to work with a glazing company that is fully qualified and certified to design with fire-rated glass. The glass itself obviously has to be fire rated but so do the fixings and any associated ironmongery.
A fire rated structural glass floor.
There may be a restriction on the maximum glass sizes that you can use when specifying a fire rated glass structure. This is due to the strict legislation around fire safety in buildings. You cannot install a piece of fire-rated glass that has not been tested to that exact size and installation.
Fire rated glass has been fully tested to be used as part of a structural glass wall, glass façade, structural glass roof or a glass floor.
Due to the lack of frame used and the bespoke nature of each structural glass installation you need to ensure that all loading requirements for a piece of structural glass have been considered.
The Line Load
A vertical glass installation of any kind will be required to be designed to withstand a certain level of line loading. This is the load of a person or people leaning on the vertical glass elevation. It is most often a major design consideration for structural glass balustrades. These frameless structural glass installations tend to be one fixed at the base, thus creating a cantilevered glass construction. It is imperative that both the glass fixing and the glass specification be designed to withstand the correct level of line loading for the project type (residential, commercial or public) as well as the height of the cantilevered balustrade.
A frameless glass balustrade to office and residential development.
The Maintenance Load
If utilising a horizontal glass structure on a project, such as a structural glass roof, you should ensure that it is designed for maintenance loading at a minimum. This means that the glass roof is designed for ad hoc access for fixing, cleaning and general maintenance.
Designing structural glass roofs for maintenance loading is not a building regulation requirement but it is highly recommended so ask your glazier to ensure the right loading has been allowed for.
A 3D structural glass roof to a prime residential development in London.
The Wind Load
Bespoke structural glass walls and facades will have to be designed to withstand both line load requirements as well as external wind loading. This is to ensure that the glass wall doesn't bow or break when exposed to high-level winds.
Building regulations require all facades be designed to withstand a wind load of at least 0.5kN. For comfort and security IQ Glass recommend designing all structural glass walls to withstand a wind load of 0.65 kN as a minimum. Areas by the coast or at higher altitude (such as penthouse or roof glass box extensions) may be required to be designed to a higher wind load. This can be investigated for each individual case.
Structural glass wall on a residential new build in Buckinghamshire.
On any structural glass wall or facade design, you have to ensure that both the glass and the fixing to the building is designed to withstand this load.
Find out more: Designing for Wind Loading
Solar Control Coatings
As structural glass installs tend to be large elements of a buildings external skin solar shading and overheating from solar gain is a large area of consideration.
The easiest way to protect a structural glass façade from excessive solar radiation is with the introduction of a solar control coating into the glass unit. These coatings are transparent and are designed to reflect solar radiant heat away, stopping it from penetrating the glass elevation.
The appearance, performance and any colouration resulting from a solar control coating will depend entirely on the coating strength that you need. The structural glass box to the IQ Glass sales office includes a 70/35 solar control coating to all the glazing. This means that the light transmission through the glass stays at 70% but the G Factor is reduced to 35%.
The Glass Box Extension to the IQ Glass offices in Amersham uses a solar control coating.
You can find out more about the G Factor, solar control coatings and solar gain in the below technical articles:
Low Iron Glass
When looking into using structural glass you must consider that the actual glass unit you will be using in the installation will be a little thicker than a similar framed installation. This is because there is no frame to support or hold the glass so it has to be a little stronger all on its own.
In some cases, the increase in thickness of glass can result in a visual increase in the slight green tint visible in any glass unit.
To remove this green hue to the glazing you can specify your structural glass to be low iron glass. Low iron glass is a purer glass product that has been manufactured with a lower iron oxide content. This creates a much clearer glass product that can be used in very thick panes and layered together with other glass whilst maintaining the clarity you want.
Low iron glass used in Drax Avenue to provide clear views of the garden.
Low Iron Glass should always be used for structural glass floors, structural glass fins and structural glass beams. It is recommended for frameless glass balustrades but not required.
Find out more about low iron glass and why you should use it here:
Elements of a structural glass installation may have to be laminated in order to achieve the correct loading requirements but laminates can also be used for a decorative purpose.
A coloured interlayer can create a structural glass wall with a bright hue. A printed interlayer can create a logo or image within a structurally glazed façade that is UV stable and safe from interference.
A green coloured interlayer to the structural glass box at the IQ Glass offices.
For something different you can laminate any material, you need into a glass unit that can then be used for any layer of structural glass installation.
Electrical Technical Glass
Heated glass, privacy glass, electrochromic glass and LED glass are all electrical glass products that can all be easily integrated into a structural glass installation. These latest advances in glass specification and technology bring additional levels of performance and versatility to a glass structure.
Heated glass can be used within a structural glass roof to remove any snow or ice load. It can be included in a structural glass wall to provide the heat source for a space. It could be incorporated into a glass roof over a pool to stop condensation building up on the inner glass face.
Structural glass walls with heated glass to swimming pool house in Cheshire.
Similarly privacy glass can create large installations of structural glass that turn transparent at the flick of a switch. Electro chromic glass is perfect for structural glass roof designs where solar gain and overheating are large concerns.
As each installation of structural glass is bespoke there are no ‘typical’ fixing details available for architects to include in their drawings. Instead, you need to speak to a specialist glazing designer.
You want to consider how the fixing detail will both connect to the building but also how they will be hidden. If your building finishes don’t allow for the concealment of fixings (if you have a brick skin or stone external finish) then clever structural glass design details can be used to ensure that the glass fixings are hidden and minimal.
On this extension to a private home in the Cotswolds, for example, the head fixing of the structural glass could not be hidden in a traditional fashion due to the light stone exterior. Instead, the glass was elongated and the structural glass fixings were pre-bonded to the inner face. This allowed us to fix the glass back to the building whilst maintaining a flush finish from the glass to the stone!
Structural Glass Wall to large home extension in the Cotswolds. The structural glass created the appearance that this large cantilevered roof is floating.
No structural glazier will give out design details before in-depth design is done, however if you meet with one of their technicians in person or visit their showroom rough ideas or sketches should be able to be produced that will help you to integrate this glass into your building. If detailed structural glass design is required before the glass is ready to be ordered the client could pay a deposit or design fee to allow the glazier to produce in-depth design details. This is often done for listed or sensitive buildings where full design details are required early on.
First of all, you should ensure that your structural glazier has an in house installation team. This means that they will be responsible for the glass installation and lifting on site so you don’t have to worry about it.
The IQ install team install frameless glass to a commercial building in Covent Garden.
On most sites the will be lifted manually with the help of specialist glass lifting equipment (make sure that this has been included in your original quotation). There may be some instances where the glass units cannot be lifted manually and a crane may be required. Such instances include large elements of roof glazing, projects using large panes of glass to the rear of a building or projects with limited access. But realistically if a crane is needed for the glass there will be other materials requiring a crane lift too. Your glazier can organise glass delivery to coincide with this to reduce crane costs.
Another major component of a structural glass install is the structural silicone. This is the element of the installation that weather seals the structure together so is vital for external glazing. Structural silicone should only be applied by experts. If the structural silicone joint on a glass install is messy, uneven or patchy then the entire glass installation will do so.
Your structural glazier should have a dedicated silicone or mastic team. This will be a separate division within their in house installation team that’s sole purpose is to visit projects and apply the structural silicone. This will ensure that adequate time and attention is spent in applying the silicone resulting in a properly weather sealed glass structure that looks great.
If you keep all of these important factors in mind you can ensure that your structural glass installation looks and performs fantastically.
For ease of mind make sure that you speak to an experienced structural glazier like IQ Glass for all of your structural glass projects. You can call the team on 01494 722 880 or email email@example.com with your query.
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