Did you know one of the largest effects on your homes energy rating is windows?  The choices made on your window selections can have a dramatic effect on the build budget and the energy rating, which is ultimately the cost to run of your home.  

When deciding on windows, saving money upfront can cost you thousands in higher energy bills over the life of your home.  With rising energy costs sometimes you can get your investment in more expensive windows back in under 7 years!

Making the right choice to suit your budget and your Energy Rating Goals requires some homework and discussion with the experts.  Today we try to share with you some information to help you be more educated.

This diagram gives you an idea of the different window frame types and how they compare between cost and how energy efficient they are, along with maintenance consideration.

Key Points

  • Thanks to growth in the uPVC market the cost of uPVC is now down to equal or better than timber in a lot of cases
  • Timber windows require an every increasing degree of ongoing maintenance.  When this maintenance isnt done, it can lead to much earlier failure of the frames.  Meaning that you are looking at a higher cost option, with a limited longevity.
  • You can see here how your options stack up with aluminium frames.

Window Opening Styles by Enduro Builder

Tilt/Turn Style Window (supplied by Double Glazed)
Tilt/turn windows supplied by Double Glazed www.doubleglazed.com


Note: Cost is a difficult metric to cast accurately as different window types can be made economically or expensively depending on the material. So use the cost information as a rough guide only.

Key Points

  • The windows with less opening points, such as sliders, seal better when built in timber, provided the timber doesnt warp!
  • uPVC windows, because of their dimensional stability and large profile frames generally come with superior multipoint locking systems.  This enables a uPVC window to be shut more securely and have double seals.  Leading to a higher performing window overall.  For more information on this check out our post about the CSIRO’s Energy Efficiency Report

So how is you energy rating worked out in relation to windows?

Have you ever heard the stories of windows having to be double glazed in order to achieve a 6 star Energy Rating?  (as an aside, excellent design can often avoid the need to be forced to use Double Glazing, its a lot better to choose double glazing to raise your energy rating to 7 or even 8 stars).

You may be familiar with R-Values.  This is a number which measures the ability of a wall, roof, floor or ceiling to insulate the home against the elements.  The higher the R-value the better the insulation.

Windows ability to insulate is measured using a U-Value.  This has an inverse relationship to R-Values.  So the lower the U-Value the higher insulating ability of the window.

In addition to this we measure SHGC (Solar Heat Gain Coefficient) of windows as its another important factor, as shown below.  One of the most cost effective ways to work around windows with high SHGC is to shade them with a fixed shade, extended eaves or pergola.

In a detailed Energy Rating the U-value and SHGC are taking into account when assessing a house.  While there are generic numbers available (the ones we have used here), it is much better to ensure your house is rated using the correct values for each window.  This ensures that your house will actually meet the Energy Rating its designed to.


What is most interesting about these figures is the difference between clear double glazed and double glazed with Low-E glass.  For a small additional investment you can achieve a 5% improvement in the amount of heat/cold gained or lost.

In this graph we have also put timber and uPVC together as they achieve roughly the same values.  The big difference which isnt accounted for here is how well they seal. Timber is prone to warping with the seasons, allowing gaps to open in frames.

You can see as we work from Aluminium through to uPVC that the U-value drops consistently while the SHGC is related primarily to the glazing type.

An example of the thermally broken aluminium window frame, you can see the breaks in green. uPVC Window Frame Example with Standard double seals Stock Standard domestic aluminium frame Another Thermally Improved Aluminium Frame

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A Guide to Window Selection