What considerations should be made on windows and doors in Canberra?

Climate Zone for Canberra

Canberra is considered to be a heating climate and we are in Zone 7, this means that we want to get the maximum sun that we can into our homes in winter and the least in summer.  Because Canberra gets so cold, we tend to run the heater while we are in the home.  Once we get the beautiful sun into our homes, we want to keep it there.  There are a several ways that you can do this:

• Replace your windows and doors with double glazed unit
• Install heavy drapes and pelmets (not much view after
• Install a second window next to the other one
• Install a piece of Perspex over the frame to create a cavity

If you are replacing your windows and doors then you want to make sure that you are getting the best bang for your dollar.  You will want a low uValue (insulation factor) – the lower the better.  The uValue measures how easily a window conducts heat, how much heat loss you will have and how well the window or door is insulated.  The measure should be overall window and frame and includes seals and spacers.

These are the common uValues for the main window choices:

Standard single glazed aluminium 4mm – 5.9

Standard double glazed aluminium 3mm/12mm air/3mm – 3.5

Thermally broken double glazed aluminium  - 2.5

Timber double glazed 4mm/16air/4mm – 2.4

uPVC double glazed 4mm/16 air/4mmea – 1.8

It is interesting to note that the uValue has the potential to improve up to approximately 0.3 stars for each unit reduction in uValue.  Each star corresponds to reduction in heating and cooling requirements by approximately 20% to 30%.  You will save approximately 10.000 to 15.000 MJ of energy per star which will save your heating bills of about $300 a year (source:  wers.net).

The frame plays a large role in getting the uValues right.   

Aluminium leaks heat and cold while timber needs to be maintained each year so that it stays in good condition.  uPVC is an insulated frame that doesn’t leak heat or cold and doesn’t need maintenance.

The other side of the coin is Solar Heat Gain Co-efficient (SHGC)

SHGC measures how much solar energy gets through the windows and doors.  It is a number between 0 and 1. The lower the SHGC is, the less heat that it transmits.

The SHGC will be relevant to different elevations in Canberra.  I would recommend a high SHGC on the north side provided there is an eave or shading in place for summer.  You want to get as much sun through the glass that you can in winter.  East and West would have a low SHGC and south won’t see any sun so you want to make sure that the uValue is very low.

SHGC can be reduced by applying selective low E (low emissivity) coating to glazing.  It can reduce heat loss in winter as well as solar gain in summer.

Glazing Calculator

If you are building a new home or extending an old one, a glazing calculator will need to be submitted to your Certifier and both the uValue and the SHGC will be required.  The figures are entered into the calculator on each orientation of the home along with shading and a green tick or a red tick will appear in the spreadsheet.  If you get a green tick you are home and hosed, if you get a red tick you need to change your windows/door or glazing.

Solace Creations at 17 Townsville Street Fyshwick and will be able to help you with these considerations and is available on 02 6260 1621.  www.solacecreations.com.au