With Glass selection there are several key factors that determine what glass to use:
- Mandatory minimum performance factors
- Other mandatory compliance factors
- Personal preferences
The first two factors are required by law via Building Codes and referenced Standards. The personal preferences can include the aesthetic look or colour of glass, high clarity seeing through the glass or privacy, further acoustic desires or protection from intrusion. Below we look at these three main factors in greater detail.
1. Mandatory Minimum Performance
The National Construction Code (NCC) dictate a buildings Total System U-Valuew and SHGCw for its Glazing. The Glazing refers to Glass + Frame + Sealants. U-Valuew focuses on the Insulation factors of the glazing (how much inside-heat it can stop from escaping out when it is colder outside). This therefore relates to the required Heating Load energy used by a building when it is cold to keep the inside temperature a warmer, healthier and more comfortable level. SHGC (Solar Heat Gain Coefficient) focuses on how much heat from the Sun enters inside through the glazing when it is hot and sunny outside. This therefore relates to the Cooling Load energy used by a building when it is hot to keep the inside temperature a cooler, healthier and more comfortable level. The requirement to meet these minimum performance factors is our first point of call when selecting glass and glazing. For proven Total System performance values using our glass types, see our AGG Estimated Total System Performance Data document, or our Speckel Glazing System Calculator, or our WERS section.
2. Other Mandatory Compliance Factors
Other required performance factors include:
- For where additional Strength is required
- To minimise the risk of Spontaneous Combustion
- To minimise the risk of Thermal Stress
- For when Grade A Safety is required
- For where additional Acoustic performance is required
Additional strength may be required in glass due to sizes of units, wind loads and human impact factors. Regular annealed float glass can be heat treated for this by either Heat Strengthening (HS) or fully Toughening (TGH), which is also known as Tempering. If you line up the three types of glass types as per the images below, you may be able to break the Annealed Float glass by throwing a stone at it with minor strength and if it breaks, it will break as very sharp and dangerous shards of glass. The Heat Strengthen glass can be 2x stronger and so now that stone may need a lot of force behind it to break, and if it breaks it will break into larger pieces that are not as sharp but still dangerous. The Toughened unit can be up to 5x stronger than the Annealed glass and may require a brick thrown at a lot of force to break it, and if it breaks is shatters into thousands of small, unsharp, safer pieces of glass.
Spontaneous Combustion is the explosion of Toughened glass due to an inclusion, like Nickel Sulphide. These inclusions can exist in the glass from its original raw materials (eg. sand) and gets primed/enlarged during the Toughening process. This can result in the Toughened glass exploding at any future point in time, even years later.
If the glass remains intact (seen in Toughened laminate) you will see a noticeable ‘butterfly’ pattern of the break style that centres around the inclusion that can be seen as a dark dot with the naked eye (see image below).
Thermal Stress is where annealed glass can crack in any future time period due to extreme temperature stress contrasts in the same piece of glass. Most commonly seen after a cold night and then strong morning sun heating up only part of the glass while the other part remains cold due to shadowing from the sun heat (eg. a tree or building casting a shadow on the glass). The risk is seen most in high solar heat absorbing glass – eg. tinted glass, tinted laminate and some dark/tinted coatings.
If the glass remains intact you will see a noticeable pattern of the break style that starts at one edge and then runs off to a 45 degree angle (see image below).
To minimise this risk, you can strengthen the glass by either Heat Strengthening or Toughening.
(For more information on see our White Paper: Heat Treatment of Glass: Spontaneous Combustion and Thermal Stress)
Grade A Safety Glass
Certified Grade A Safety glass in line with AS 2208: Safety glazing materials in buildings is ether Toughened glass or Laminated glass. The Laminate can be with either annealed glass, heat strengthened glass or toughened glass. This includes standard laminates, white translucent laminate, acoustic laminate like Audioshield®, security laminate like IntrudaShield® and IntrudaShield Ultra® or structural laminate like SkyGlass® and SkyGlass Ultra®.
Where a building will be next to a permanent noise offender (eg. Train Station, Motorway or Airport) an acoustic consultant may find it necessary to impose a minimum acoustic performance of the glazing. This is usually depicted as a minimum average weighted sound reduction decibel blocking value (Rw). When it comes to noise, you want to make sure you know what type of noise you want to block. Low base type noise is low frequency hertz (Hz) while treble type noise is high frequency. Mass (thicker glass make-up) is good for blocking low frequency noise while acoustic laminate is ideal for blocking mid-high frequency noise. Combine the two if needing to block a full range of different noise types. So Weighted Average Rw figures alone can be misleading if you do not identify the noise type and look at the dB blocking factor in that frequency range. See our Audioshield® brand of high performance acoustic laminated glass for more detail.
3. Personal Preferences
A specifier or owner of a building may also have their own preferences with the glass and glazing used. These include:
- Wanting as Clear looking glass as possible with high Clarity to either see a view from inside or be able to see inside a building without disruption – but you must also be mindful of the effect such glass has on the sunlight/glare factor coming into the building for those working and living in the building as well as unwanted results of curtains/blinds being drawn either completely or staggered across a larger building
- Coloured glass (toned or tinted) to have a desired look from the outside – but you must be mindful of the effect on Visible Light Transmittance (VLT) that coloured/darker glass plays and the resulting outcome on health and comfort levels for those inside
- Darker Coloured glass for privacy reasons – again being mindful on the effect on Visible Light and be prepared of the opposite privacy factor at night when internal lights are on
- Further Acoustics for any noise sensitive people that may live or work in the building or a known noise offender that may cause discomfort – here thicker glass and/or acoustic laminate can be an effective solution (see Audioshield® for more details)
- Protection from fading factors from harmful UV from the Sun to protect; timber floors, carpets, important documents, books, certificates, diplomas, paintings on the wall and other artwork – here any laminated glass product would be an effective solution (see AGGLam® for more details)
- Further Security from intrusion – here an advanced laminated product may be an effective solution (see IntrudaShield® and IntrudaShield Ultra® for more details)
It is also important to note that sometimes personal preferences may not be allowed due the mandatory requirements that must be met. A common example here is wanting very Clear glass with High Clarity and High Visible Light and yet the minimum Total System SHGCw value required is so advanced that such a desired glass cannot satisfy.