Different window glass types

At its most basic level, all glass is made by heating sand until it melts and turns into a liquid. By changing the ingredients or process, or adding different coatings, the colour, strength and other properties of the finished glass can be altered, making it useful for a range of situations.

Most window glass is made using the float glass process. A sheet of molten glass is ‘floated’ on a bed of molten metal to create glass that is smooth and flat with a uniform thickness. The colour of glass can change depending on the mix of raw materials used. Low iron content, for instance, will produce extra-clear glass.

This guide introduces the most common types of glass used in windows and doors in New Zealand.

Low E glass

Low E Glass is low emissivity glass. Emissivity is the rate at which heat leaves a building, therefore, Low-E glass has a lower rate of heat-loss compared to glass that is not Low-E.

The main difference between a Low E glass and an ordinary glass is that Low E glass has extremely thin layers of silver or other low emissivity material applied to one side of the glass. This enables a reduction in the transfer of heat or cold through the glass. Think of it as an invisible insulation barrier for your windows. Just as wall and ceiling insulation provides protection to those areas, Low E glass does the same for your windows. Low E coated glass helps provide a more comfortable temperature in a room, more window area can be designed into your home, and heating and cooling costs are reduced.

Due to its sensitivity, Low-E glass needs to be created within an insulated glass unit.

Considerations for Low E glasses include:

  • Low E glass needs to be enclosed in a double or triple glazed unit to protect the coating, but the benefit is that you get a better performing product. So, you can have bigger windows with more energy efficient outcomes.
  • Double and triple glazed units must be installed a certain direction to support their performance, your window installer or glazier should ensure this when building your windows.
  • Some Low E glass has haze characteristics (hard coat vs soft coat), so if this is a concern discuss your needs with your glazier.
  • Low E glass is available in a range of thermal performance levels, so discuss the needs of your project with your glass supplier.

Glazing with lead lights

Lead lights are a popular traditional form of decorative glazing that adds character to windows and doors. The New Zealand Building Code allows lead lights to be used wherever annealed or safety glass can be used; there are, however, some limitations around the maximum individual pane size and total area of the lead-light glazing that can be used.


Safety glass

Glass is classified as a hazardous building material in the New Zealand Building Code, and safety glass is mandatory in areas that are identified as being at high risk of human impact, such as bathrooms, and for doors and larger windows. There are two main types of safety glass used in New Zealand. Both will help protect you and your family from serious injury if the glass breaks for any reason.

Laminated safety glass contains a thin layer of vinyl, which keeps the pane intact if it is broken.

Toughened glass is treated to make it extra strong, and will break into many small cubes instead of blade-like shards if it is shattered.

Safety glass will either be laminated glass or toughened glass and can be identified by a compliance logo marked with NZS 4223.3 in either permanent ink or an etch-marking. If there is no marking, it may not be safety glass and should be replaced.

Learn More about Safety Glass