August 27, 2021

Revised Datasheet on IGU visual quality

Revised Datasheet on IGU visual quality

The GGF is pleased to announce the launch of the revised GGF Datasheet 4.10, Appearance and Visual Quality for Insulating Glass Units (IGUs).

Data Sheet 4.10 details all of the appropriate optical and visual quality factors of the glasses used to manufacture the IGU, that influence the appearance of an installed IGU.

The most important criteria is the view through the IGU from the inside of a building, which is covered in detail. However, it is appreciated that the appearance from the outside of the building (i.e. in reflection) can also be important in certain applications and Data Sheet 4.10 also makes reference to this.

The origins of glass visual quality standards and why GGF Data Sheet 4.10 is the go-to document:

The standard for float glass in Europe in EN 572 Glass in Building – Basic soda lime silicate glass products.  Part 2 defines optical and visual faults and the relevant acceptance levels. The viewing distance for standard float glass is 4.5 metres.

A glass manufacturing float line typically produces around 700 tonnes per day.  The raw materials are mixed and melted down at high temperatures within a refractory lined furnace. The molten raw materials are then floated on a bath of tin and moved through the float line to create a continuous ribbon of glass.

Most glass installed within buildings is manufactured from float glass in accordance with EN 572. In many installations the glass requires additional processing to provide the correct performance in terms of safety, security, and energy requirements.

Glass can then be coated to provide a specified level of solar control or thermal insulation, screen printed, coated with ceramic frit or the surface altered, to provide decoration or privacy.

In addition to this the glass may undergo a heat treatment processes to add certain characteristics. It can be thermally toughened for increased strength and safe fracture behaviour, heat strengthened for additional strength, heat soaked to reduce the risk of spontaneous breakage when installed on site, or laminated for safety, sound attenuation and security. 

All of these additional processes involve changes to the original float glass product and usually results in varying amounts of alteration in the visual quality and appearance of the products. The visual quality rules in EN 572 are no longer applicable so we need to look elsewhere.

For Thermally Toughened Glass manufactured in accordance with EN 12150, the standard does not contain any visual quality limits but does stipulate that visual inspection should be included during the manufacturing process. However, the standard does mention the existence of roller wave, pitting and anisotropy, but does not define any limits regarding these characteristics. This is the same for Heat-Soaked Glass Manufactured in accordance with EN 14179.

For laminated glass the standard is EN ISO 12543 Glass in Building – Parts 1 to 6. Part 6 details the appearance and defines vents, creases and streaks, spots and linear defects and the levels of acceptance. The glass is visually inspected at 2 metres under normal daylight conditions.

Coated Glass in accordance with EN 1096 defines uniformity, stains, spots, pinholes and scratch faults and the acceptance levels. The glass is viewed from a minimum distance of 3 metres for no more than 20 seconds.

Heat Strengthened Glass in accordance with EN 1863 states that the processor is responsible for determining the visual quality standards to be used for their products. However similarly to EN 12150 and EN 14179, the standard does mention the existence of roller wave and anisotropy but does not define any limits regarding these characteristics.

As you can see depending on the products used, negotiating visual quality may not be as straight forward as it may first seem. This is where GGF Data Sheet 4.10 steps into a very important void. It covers all of the above-mentioned products, as well as visual phenomena’s that may be encountered with flat glass products. It is the only recognised visual quality standard within the UK for visual quality of installed insulated glass units. It is also widely used across Europe and the Middle and Far East. This mean 4.10 is one of our most important Data Sheets.

4.10 has been updated to incorporate the latest changes within BS, EN & ISO Standards so GGF members can continue to be the leading experts within the industry. The Consumer facing visual quality leaflets are also due to be updated in 2021.

The Data Sheet can be downloaded from the members area of the website within the glazing manual.  Click here to access

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