What is double glazing, and how does it work?

Nowadays, more and more new building requires at least 6-stars energy efficiency for there windows and doors. Glass is the potential weak point of a building in terms of energy efficiency. A single glazed window can gain or lose up to ten times more heat than an insulated wall. The market needs high energy performance windows products. Double glazing is the best option. However, double glazing is totally different to single glazing. In this article, you will be introduced to the differences from structure to installation. Good installation is the key to a perfect window.


This photo shows the double-glazing units. Insulating glass (IG), more commonly known as double glazing (or double-pane, and increasingly triple glazing pane), consists of two or three glass window panes separated by a vacuum or gas filled space to reduce heat transfer across a part of the building envelope.

The photo below shows the spacer between double glazing. This is a combination of normal spacer and desiccant. The desiccant will remove traces of humidity from the air space so that no water appears on the inside faces of the glass panes facing the air space during cold weather. The units are then sealed on the edge side using silicone sealant.

Compared to single glazing, the double glazing edge is sealed by silicone. Single glazing can be butt joint in the corner. Double glazing would have a small square in the corner.

There is also a limitation of double glazing maximum sizes. Areas of a home that are prone to accidents are required to be fitted with what’s known as Grade A safety glass. The use of safety glass reduces the risk of injury as it is tougher to break and won’t fracture into dangerous shards if broken. In recent years the areas of your home where safety glass is required has increased, while the allowances for ordinary glass areas has decreased. AS1288-2006 shows that Grade A safety glass by using toughened, laminated glass in 6mm thickness should be no more than 4 sqms. For double glazing, the formula calculates the result for 4.5sqms. But it is strongly recommended to use 4sqms at most. It is already a huge and heavy pane.


For installation, through sliding doors and bi-folding doors:

The first potential issue to arise is level problems. When doors and windows frames are installed as per instruction, all door and window sashes should be installed according to the frames and be kept consistent horizontally and vertically. This is very important for moving panes. If the frame is not level, how can the panes move smoothly?  A level ruler is not enough for a door width over 3meters. A laser level machine is needed.

The second issue is sub-sills. Sub-sills must be installed firmly in order to sustain and support the weight of sliding door frames and sashes, to prevent potential sinking of the frames under weight pressure.

The last one is building structure. In some instances, due to the fact that some building structures or building weight bearing capacities are not enough to support the bifold doors or sliding doors, there’s the danger of warping of the frames, causing issues with operation of the folding or sliding sashes. Please be advised that architects and engineers need to evaluate and confirm the lintel weight bearing capacity above the door frames to ensure there’s no potential sinking of the lintel.


Fantastic building consists of good quality windows and proper installation. The proper installation of a window is equally as important to the total performance of a window as the manufacturing process and materials used.