There are many types of infill panel available for your balustrade, such as mesh, perforated aluminium sheets, vertical bars or timber. However, the type of infill panel we’re most interested in, and focus of this article, is glass.
Glass Infill Panels
Typically, glass infills provide a more cost-effective solution than other panel infills like mesh, perforated or vertical bar panels – despite giving a high perceived value and a more desirable aesthetic appearance. Glass balustrades are discreet and offer unimpeded views, let light in and give a high-class appearance. Click here for a deeper dive into the different types of glass, and their uses in balustrading.
Timeless and elegant, glass offers the perfect balance of light, visibility and safety. We offer a range of thicknesses and variants, including privacy, tinted, self-cleaning, low-iron and laminated glass, plus coatings and films for enhanced performance. These options are available for both framed and frameless glass balustrades.
As required by BS 6180: 1999, glass in freestanding barriers needs to be either toughened, or toughened and laminated, both conforming to BS 6206.
Toughened Glass
Toughened glass is four to five times stronger than annealed glass of the same thickness and is ideally suited to most safety critical applications. However, its use at high level must be subject to careful consideration because if it is broken, the glass will shatter into tiny pieces and will no longer support a load or act as a barrier. (Toughened glass should fragment into small, non-injurious pieces, quite unlike the razor sharp shards of broken annealed glass.) Since the devastating Grenfell disaster, there have been various changes to the regulations regarding use of fire resistance materials at heights of over 18 metres. Click here for more information regarding whether glass is a combustible material.
Toughened & Laminated Glass
Toughened & Laminated glass consists of sheets of toughened safety glass bonded together with a tough plastic interlayer which enhances safety and security as well as retaining glass fragments in the event of breakage. It normally consists of two panes of glass and either a clear:
- PVB Interlayer (Poly Vinyl Butyral) is the most common type and is suitable for most applications or
- SGP (SentryGlas Plus, a registered trade mark of DuPont) could be specified for exposed or potentially ‘dangerous’ environments; this may be up to 5 times stronger than a PVB interlayer.
The principle benefits of toughened & laminated glass are its strength and performance under impact. It is capable of withstanding very large loads and in the unlikely event of being broken the resulting fragments will be retained by the interlayer. When properly glazed, it will normally remain in place until replacement is convenient.
White Metal recommends the use of a capping with large units of laminated glass, as panels can occasionally be mis-aligned leaving unsightly edges. There is an allowed tolerance of misalignment during the manufacture process, and this is regulated by the GGF.
Clear toughened laminated glass has a slightly lower light transmission than ordinary glass of the same thickness. It is thermally safe and will resist high temperatures without breakage. Toughened & laminated glass is available in a wide range of glass, interlayer and thicknesses and can be used to satisfy all safety glazing requirements of Approved Document N of the Building Regulations and BS 6262 part 4. Subject to calculation it can be used to form full height barriers, infill panel barriers as well as free standing barriers (structural balustrades) in compliance with Approved Document K of the Building Regulations and BS 6180.
Heat Soaking
For additional safety, glass can also be heat soaked which reduces any possibility of spontaneous fracturing caused by nickel sulphide inclusions.
Nickel sulphide inclusions are formed when a minute nickel rich particle mixes with sulphur during the melting process. These inclusions tend to be smaller than 0.3mm and are not readily visible. It is estimated that in a normal glass production run, nickel sulphide inclusions occur at a rate of one per eight tonnes of raw glass produced. Nickel sulphide is impossible to eliminate and all glass has some present.
Nickel sulphide spontaneous breakage of Annealed or Heat Strengthened glass is highly unlikely do to very low stresses in Annealed Glass and a controlled stresses in Heat Strengthened glass.
However in toughened glass, the heated glass is cooled at a much higher rate, to achieve the required internal tensile and surface compression stresses. Because of this high cooling rate these inclusions do not have time to return to their original state but remain in a high–temperature state within the glass. Over time these inclusions will return to their low-temperature state, and in the process they increase in volume causing additional stresses within the glass and eventually causing a spontaneous breakage.
Heat Soaking is destructive process where toughened glass is subjected to a temperature of 290 degree Celsius for several hours in a “Heat Soaking” oven. During this time, the nickel sulphide inclusion undergo a phase change and reverts back to its original low-temperature state. This basically means that any nickel sulphide inclusion expands in volume. If this inclusion is near the central tension core of the glass, the change in volume will generate sufficient stresses to break the glass.
It is estimated that up to 95% of nickel sulphide contaminated panes of glass are usually destroyed by this process reducing the chance of on-site spontaneous breakage.
Special Design Applications
Special interlayers include sound control, privacy and decorative effects. Patterned and tinted glasses can be laminated and materials such as film, wood, fabrics and metal can be bonded between the panes to create unique finishes.
However, specialist interlayers are more costly, and usually have longer lead times than standard laminated glass. It can be very difficult to match existing colours and finishes with toughened & laminated glass, so it may be that we require a sample of the glass to be approved before proceeding with the whole order.
