Frameless Structural Glass Balustrades
The first option and the preference for the majority of projects have been frameless balustrades (also known as frameless structural glass). Frameless structural glass provides the means to achieving an uninterrupted view from the balcony itself, with a minimalistic appeal when looking from the ground up.
There are three core parts to frameless structural glass balustrades; the base fixing, the glass, and the handrail (or Capping). These sections explore each in turn.
The design of the Cassette® balcony system makes for a rigid base fixing to be achieved simply, whichever specification of structural glass is specified.
The second critical design consideration is the selection of glass itself. This needs to designed to perform to structural requirements for deflection, loading and impact, whilst providing optimal safety to users on the balcony and persons below.
Glass can also be used decoratively to create effects or to introduce more privacy for users and prevent wind on balconies.
In the UK it is currently banned by the fire regulations if using a laminate glass interlayer. To find out more and understand if it is a safety issue or a safety benefit view our laminate glass whitepaper which was written for the UK government. Alternatively, you can view a video recording of UK glass experts debating the use of laminate glass in structural glass balustrades on balconies. It is available to view at www.resi.build
The base fixing of frameless structural glass is the first of the three considerations for the balustrade design.
Whilst the glass choice and the base fixing need to be considered together, rather than isolated, we start with the base fixing choices. These govern how the balustrade will be connected to the Cassette® and is the part of the balustrade which will most affect the aesthetics. Primarily because the fascia options stem from which base fixing method is chosen.
Using a mechanical fixing which has bolts going through the glass and into point fixings (or Bobbins) behind is the most common solution in our experience. This is because of its simplistic nature with neat aesthetic appeal.
A neat fascia can be connected to the front of the base clamp using a hidden clamp plate, which offers a neat line to finish the balcony. Alternatively, a band of ceramic print can be applied between the two layers of glass which hides the detailing behind. Discs on the front would typically be powder coated to match with the band. This solution typically offers cost savings compared to the fascia option.
When a balcony has a fascia, the mechanical base fixings still uses point fixed ‘Bobbins’ behind the glass, but in front of the glass, a special clamp plate is used.
These plates sit in front of the glass and span between the two point fixings, clamping the glass to the point fixings. The fascia’s hook around these special clamps and have bolts screwed in from above the clamps.
The fascias have drainage slots at the rear face so that any water which collects inside them can drain out.
Wedge fixing of glass can often be an expensive solution for balconies when compared with mechanical fixing.
Sometimes it is chosen by clients when using a heat strengthened glass. This is often because heat strengthened glass isn’t as strong as temper toughened glass, and by wedging the glass, less pressure is applied than with point fixed “Bobbins”.
We have also developed a wedge fixed channel profile, which provides a fixing channel and a fascia incorporated into the same extrusion.
Glass overview and Balustrade Design Choices
The second key choice with frameless structural glass is the glass itself.
Both monolithic and laminated glass must always be toughened to comply with regulations.
Whilst either monolithic or laminate toughened glass can be used, toughened laminate has fast become the most popular choice for balconies, primarily because of its safety benefits. (I.e. if one pane smashes the other stays in place and will captivate most fragments in-situ. BS 6180 requires two forms of guard which are capable of withstanding the same load, however allowance is made for using laminated glass which enables slim cappings to be used instead of larger handrail profiles.
One of the aesthetic benefits of using laminated toughened glass is that the interlayer can be used to create solid or translucent effects. Whether for privacy or as part of the building’s architectural appeal.
The most common type of interlayer for balcony glass is PVB often chosen for its balance of cost and performance. The use of obscure laminates typically provides a more consistent, durable, and cost effective solution than films, which are applied to the glass after installation. Unlike films, the interlayer is protected between the two layers of the glass.
In addition to using laminate interlayers, there are other choices which can be made to enhance the glass, or to create privacy.
Float glass can also be processed from specialist raw materials including; pre-tinted glass, pre-etched satin glass or low Iron glass. All of which are typically expensive. Iron in glass is typically what gives it a slightly green tint, most visible around the edges. Low iron glass is an extra clear version which can usually be identified by more blue coloured edges. Printing is also an option either as solid, frit or bespoke patterned using screen print, digital print, roller print or back painting.
When using monolithic glass, a handrail needs to be specified to perform a second guarding in line with BS6180. Capping’s an only be used with laminated toughened glass as they don’t perform a structural duty.
By far the most common option is the square aluminium capping. The advantages are, firstly that they can be extruded in a single 6m length, unlike bespoke metal cappings which are made from a sheet. Secondly, the aluminium extruded sections have special groves built in, these allow innovative locking joiners, and end caps to be slid into place.
Extruding is more accurate and consistent than sheet metalwork, which need more tolerance because of material variance, tooling, settings, etc. Aluminium cappings can be powder coated or anodised, however, the most common choice is to use a brushed anodised finish to look like stainless steel.