What To Consider When Specifying Structural Glass
When looking to include structural glass on any project there are various elements of design, logistics and specification that you will need to keep in mind.
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.
Glass Performance
One of the main advantages of a structural glass installation is that it is frameless. This means that the glass is the only major factor when it comes to performance. You need to ensure that the glass specified for the glazing achieves all of your design criteria for thermal, acoustic, solar radiation and appearance.
Thermal Insulation
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.
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?
Acoustic Reduction
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.
Fire Rating
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.
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.
Loading
All structural glass installations should be designed by a specialist glazier with many years of experience in structural glass design. As there is no framing system or standard details each project will have to be considered and detailed on an individual basis. If these design details are not realised fully the glass installation may not withstand all the demands required.
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.
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.
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.
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
Glass Specification
In addition to the performance and structural needs of your installation you should also think about the additional visual elements of the glass. Specialist glass finishes can be achieved from structural glazing using a wide variety of coatings and decorative glass techniques.
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%.
You can find out more about the G Factor, solar control coatings and solar gain in the below technical articles:
How to control the increase of the temperature in a space or building as a result of solar radiation
What is Heat Gain and how can you control it?
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 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:
Why should I specify Low Iron Glass?
Laminated Glass
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.
For something different you can laminate any material you need into a glass unit that can then be used for any layer of a structural glass installation.
Electrical Technical Glass
Heated glass, privacy glass, electro chromic 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.
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.
In any case if you have a specific requirement for your glass installation it is best to speak to an expert. Your chosen glazier should have in depth knowledge about each of these glass options and they should be able to provide you with advice as to how to achieve the appearance you need.
Fixing Details
Even though the fixing details on a structural glass unit are hidden that doesn’t mean that they are any less important a factor in its design. In fact some could argue that they are the most important element of a structural glass project.
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!
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.
Installation and Access
Most structural glass installs will be utilising large panes of glass. How these large panes of glass get to site, how they are manoeuvred into place and how they are installed can be tricky.
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.
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.
And Finally…
Remember that not every company offering a ‘structural glass service’ will have the requisite number of years’ experience in the field of structural glazing so do not rely solely on them to consider all of your options.
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 hello@iqglassuk.com with your query.
Originally published at news.iqglassuk.com on October 17, 2017.
