What is Double Glazing?

Double glazed units are also known as Insulated Glass Units (IGU).  They are just as important to your home as the batts in your walls and ceiling.  They mainly insulate your home against heat loss and with a change to the glass makeup can reduce heat coming into your home.

Standard double glazing will not stop the sun coming in during winter.  This is one of the most commonly asked questions from our clients.  You need the sun to come into your home so that you can benefit from the free heating. Double glazing lets it in and then traps it in the home.

The important component of an IGU is the airgap between the two glass panes.  The gap is filled with either air or an inert gas which is a much poorer conductor of heat than the glass. This means that less heat will escape through an IGU than a single glazed window.  Think of IGUs in the same way that you think of wall insulating batts.  The air trapped between the two panes of glass forms an insulating layer between your home and the cold outdoors.

Insulated Glass Units can also be triple glazed, however, this is not as popular in Australia as it is in Europe.  The drawing below is a simple explanation of a double glazed unit:

Drawing Source:  Wikipedia

1, 2, 3, 4 - Glass pieces in the unit

There are two pieces of glass in the unit with four sides and the sides of the glass units are named to avoid confusion when making the glass.

Surface 1 is on the outside pane and faces the outside
Surface 2 is on the outside pane and faces inside
Surface 3 is on the inside pane and faces outside
Surface 4 is on the inside pane and faces inside 

5 - The Window Frame

This is the window frame and this topic will be a separate post.  The frame can be aluminium, timber, uPVC, fibreglass or a composite.

6 - The Spacer Bar

Double glazed units are put together in the glass factory, they are not assembled at the building site or home. The two pieces of glass are held together with an aluminium or insulated spacer bar that seals the space and keeps the glass in place.  The bar goes between the two pieces of glass and is of various widths.  The optimal spacer bar for effective insulation is between 10mm and 20mm.  The bar has desiccants inside to prevent humidity and condensation between the two panes of glass.

The double glazed unit can be made up of various components to keep the heat out, keep noise out or in and increase security.  This will be a separate post as there is a lot of information to consider.

The sides of the glass units are named to ensure they are made up correctly.

Surface 1 is on the outside pane and faces the outside
Surface 2 is on the outside pane and faces inside
Surface 3 is on the inside pane and faces outside
Surface 4 is on the inside pane and faces inside 

7 - Seals

The seals are attached to the frame and press up against the glass unit to stop airflow.

8 - Timber Reveal

This is also known as your window sill. 

9 - External Sill

This is the external window sill.

Air versus Argon Gas

Most double glazed units are air filled, however, it is becoming more common place to inject an inert gas like argon.  Argon is injected into the double glazed unit in the factory and sealed to prevent leakage.  Argon gas is an even poorer conductor of heat and conducts about 33% less heat than air.  There is some research to suggests that gas leaks over the years, however, it is at a very slow rate if any.  The price of argon has reduced and it is now very affordable.  Some companies provide the argon fill as a standard feature.

Summary

In summary, double glazed units are just as important as wall, ceiling and floor insulation.  They trap air between the two panes of glass and this is the insulation.  They let the lovely warm sun in and then they trap it inside.  It is important that you always use sealed double glazed units as they stop condensation and provide a better insulation rating.  Some people retrofit by placing another piece of glass into the window and this is not as effective as the sealed units.

The spacer bar is important.  You want to make sure it is between 10mm and 20mm. If they are too close together heat can easily transfer from one side of the window to the other which provides less insulation (just like the thickness of your batts).  If they are too far apart then the air can move inside the two panes which provides less of an insulator.

Karen

17 Townsville Street Fyshwick

www.solacecreations.com.au