GLASS BALUSTRADE

Glass is generally considered the best material to use for balustrade on balconies due to a number of reasons as stated below:

Relatively low cost

Long life span

Low maintenance

High strength

Wide range of colours

Easily customised/printed.

Regulations and standards for glass used in buildings can be considered to fall within three categories. Each of the glass types of barrierrequires differing design loads and therefore, differing glass specifications:

• Freestanding glass protective barriers

• Barriers with glass infill panels

• Full height glass barriers (not usually applicable to balcony design)

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The forces the glass must be designed for are: Line load (Horizontal UDL) kN/m2, uniformly distributed load (UDL) kN/ m2, concentrated load kN and Impact Force. With a framed balustrade containing glass infill panels the balustrade frame, rather than the glass, needs to meet the line load.

Tempered glass, or toughened as it is typically called, tends to be the most popular choices for balcony balustrades whether framed or frameless. Tempered glass and heat-strengthened glass are relatively similar in the way they are processed.

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The main differences are typically:

• Impact resistance  Tempered glass has an accelerated cooling process which creates a higher surface compression. This makes the surface around four or five times as strong as untreated glass. The heat strengthening process is slower, meaning compression strength is lower and making it twice as strong as untreated glass.

• Manufacture  Because of the slower cooling process of heat-strengthened glass, it requires more control and is therefore typically harder for glass processors to get right than tempered (toughened) glass.

• Fragmentation  Typically the higher the surface compression, the more pieces the glass will fragment into (if it is laminated this can significantly change the fragmentation pattern). Therefore temper toughened glass will fragment into smaller particles whereas heat strengthened glass will fragment more like annealed/untreated glass.

• Vulnerability to NiS breakage  nickle sulphide can occur in both tempered toughened glass or heat strengthened glass. However, because the surface compression of heat-strengthened glass is much lower than temper toughened glass it makes NiS much less likely to cause a spontaneous fracture in heat strengthened glass.One way to reduce the risk of NiS is though heat soaking (takes place after the glass is strengthened. Heat soaking involves exposing the tempered glass to elevated temperatures for some period of time. A typical heat soak process elevates the glass temperature to 550ºF (290ºC) for two hours. Reference BS EN 14179-1 standard. The obvious objective of the heat soak process is to achieve a “break now, not later” result, based on the assumption that any glass panels with inclusions will break during the heat soak process. While there is general agreement on the concept and intent of the heat soaking process, there is not agreement on the outcome. Most agree that heat soaking can eliminate (by destruction) some of the problem panels, but not that heat soaking will guarantee 100% elimination of potential spontaneous breakage due to inclusions

Greening: Sometimes you may see glass with a green tint to it (unintentional) this occurs naturally and caused by iron oxide. This often happens due to using low quality sand in the production of the glass.

What is laminated glass?

Two layers of toughened glass are joined with an interlayer providing the benefit of a second form of guarding preserved by the remaining panel until a full replacement can be made. This enhances both the safety of the balcony it is guarding and the balconies or areas below. Laminated Glass is typically considered to offer the best panel security for glass balcony balustrades.

It is important to note that what is typically referred to in the industry as “laminated glass”, is usually temper toughened glass which has also been laminated, not normally untoughened laminated glass.

Heat strengthened and laminated glass is less common for balustrades, but more common in glass floors (chosen for its larger fragmentation pattern if broken). Untoughened or annealed glass which has been laminated together is rarely used for balconies, occasionally it will be used for special scenarios (e.g. where the glass forms a tight curved radius).

Why use laminated glass on balconies?

One of the main benefits of using laminated glass (as noted in BS 6180:2011), is that when monolithic glass breaks it will smash into small particles which are not contained, whereas the interlayer of laminated glass will hold the majority of particles in most typical breakages.

Another benefit of using toughened and laminated glass is that BS6180:2011 8.5.2 states that a handrail should be used unless a laminated toughened glass is used. This allows a minimalistic aesthetic appearance to be achieved.

What are the types of interlayers?

• PVC (Poly Vinyl Butyral) is the most commonly used interlayer in glass balcony balustrades. This is because it offers a good balance between being cost-effective, offering a relatively good edge detail, performance and durability. PVB is available in a very extensive range of colours and designs enabling glass to be coloured, tinted, obscured or patterned very effectively.

• CIP (Cast in Place) is not a laminated interlayer sheet, but rather a poured resin. Sapphire does not recommend the use of CIP panels because the edge finish typically looks messy and requires concealing the edges strips due to the tape used around the holes and edges to contain the resin.

• SGP (SentryGlas Plus), a registered trademark of DuPont could be specified for exposed or potentially ‘dangerous’ environments; an SGP interlayer may be up to 5 times stronger than a PVB interlayer. In our experience, it is typically a very costly option. It comes in sheets rather than rolls like PVB often meaning there is high waste for balustrade glass production.

• EVA (Ethylene Vinyl Acetate) is not as common as PVB and is from our experience more expensive. It is typically used to encapsulate other components, such as LED lighting, into glass and offers the benefits of being less water absorbent.

Despite Laminate glass being in our opinion the best glass for balcony balustrades, it is currently based under the combustible cladding ban. (BS EN 13501-1)

 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.

Mechanical Fixings

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

Mechanical fixings with fascia's

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 fascia's 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.

Handrails/Cappings

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.

Whilst we do a number of different profiles (square, round etc) our most common is a rectangle handrail which slopes inwards. This is a safety feature we developed to ensure if anything rested on the handrail is knocked, its more likely to fall within the balcony.