What is LowE Glass?
LowE is coated glass. The ‘E’ stands for Emissivity, think of this as non-sun heat transfer through the glass. If it is a low heat transfer, then there is something special about that glass that stops this heat going through it. There are 2 types of LowE; traditional Hardcoat LowE or more modern Softcoat LowE.
What is the difference between Hardcoat LowE and Softcoat LowE?
Hardcoat LowE has been around for a long time. It is techcnially called a Pyrolytic LowE and uses a Chemical Vapour Deposition (CVD) process to spray on the coating when float glass is being made. While glass is still red hot the mixture is sprayed on and becomes part of the annealing process and embodied in the glass itself, hence the term Hardcoat. The main performing metal in a Hardcoat LowE is Indium Tin Oxide (ITO) and this LowE can be used single glazed with the coating exposed to the inside of the building. This boasts some of the best possible performances for a single glazed glass product (ie. U-Value and SHGC). Note that this also comes with challenges though as the coating can be touched, scratched and affected by cleaning products. Care must be taken for this application and note there is a risk of a haze appearance with such product.
Softcoat LowE is techcnially called Sputter Coated LowE and uses a Physical Vapour Deposition (PVD) process to sputter atomic layers of metals and metal oxides onto already made flat float glass, hence the term Softcoat. The main performing metal in a Softcoat LowE is Silver (Ag) which can allow a clean clear look without the risk of Haze and also higher performance compared to a Hardcoat LowE. Note however that a Softcoat LowE cannot be used monolithically (single glazed) and must be used in an Insulated Glass Unit (IGU) like a Double Glazed Unit (DGU). This way the coating is protected inside the air gap and not exposed. Softcoats can be further broken down into 3 main categories; Single Silver, Double Silver and Triple Silver (referring to how many layers of Silver are in the total coating layer stack. Single Silvers are generally used for residential buildings with higher Visible Light Transmittance while Double and Triple Silvers are for more advanced performance and Commercial buildings.
What is regular float glass made of?
The main way common glass is made is by the Float Plant method that sees glass float on molten tin during the manufacturing process. This allows flat glass that we know as todays regular glass. It has a several names also; Float, Float Glass, Clear, Clear Glass, Clear Float Glass, Annealed Glass… the key ingredients to regular float glass are:
- Silica Sand
- Soda Ash (Sodium Carbonate)
- Salt Cake (Sodium Sulphate)
- Cullet (broken glass)
What is Heat Treated glass?
Regular float glass is also known as annealed glass. This can break into very sharp and dangerous shards. Heat Treating this type of glass is conducted by a glass processor and can be either;
- Heat Strengthened
- Toughened (aka Tempered)
- Heat Soaked
What is a Grade A Safety Glass?
Grade A Safety glass can only be either Toughened Glass or any type of Laminated Glass that is certified to AS 2208. Laminated glass can use either regular annealed glass, heat strengthened glass or toughened glass as it is the interlayer that makes it Grade A Safety.
What is U-Value?
The ‘U’ is the thermodynamic symbol for Internal Energy. Think of this as a measure of Insulation – how much heat escapes through the glass per m2 when it is colder outside than inside, as heat wants to move from where it is hot to where it is not.
The bigger the temperature difference between outside and inside and the bigger the glass m2, the more heat will escape. This also measures non-sun heat from outside that enters in. This occurs at night after a long hot day as materials like the roads, footpaths, bricks and stone absorb the heat and when the sun goes down, this heat re-radiates and wants to enter your building (where it goes from hot to not).
The lower the U-Value, the better the Insulation and note that there is glass-only U-Value (Ug) and there is Total System U-Value (U-Valuew) = glass + frame + sealants. The NCC codes dictate Total System U-Valuew.
What is SHGC?
Solar Heat Gain Coefficient. This is a measure of Solar Control – how much heat from the sun enters inside the building through the glass. You can think of this as a % so an SHGC of 0.84 is 84% of heat from the sun enters inside (therefore 16% is blocked) while an SHGC of 0.27 is 27% of heat from the sun enters inside (therefore 73% is blocked).
The lower the SHGC, the more passive heat from the sun is blocked from coming inside. The higher the SHGC, the more passive heat from the sun enters inside your building (which can be beneficial in colder climates).
Note that there is glass-only SHGC and there is Total System SHGC (SHGCw) = glass + frame + sealants. The NCC codes dictate Total System SHGCw.
What are the most common AS glass standards?
- AS 1288 – Glass in buildings (covers general glass factors)
- AS/NZS 2208 – Safety glazing materials in buildings (covers both Toughened and Laminated Safety glass)
- AS 4666 – Insulting glass units (covers IGU’s including Double Glazing)
- AS/NZS 4667 – Quality requirements for cut-to-size and processed glass (covers quality and inspection factors)
- AS 4055 – Wind loads for housing (covers wind load factors for common residential buildings)
- AS/NZS 1170.2 – Structural design actions: Wind actions (covers wind load factors for commercial buildings)
- AS 3959 – Construction of buildings in bushfire-prone areas (covers Bushfire Attach Levels – BAL)
- AS 2080 – Safety glass for land vehicles (covers safety glass used in land vehicles)
- AS 2047 – Windows and external glazed doors in buildings (covers deflection, operating force, air infiltration, water penetration and ultimate strength testings of Total System glazing suites)