With the push for better energy efficiency within a home the cost of building that dream home is quickly becoming a greater expense than most of us can afford comfortably. The idea behind building more efficient homes is all about reducing our overall footprint by reducing the need to use more energy and in turn reduce our energy costs, but at what expense?
Most of us know that choosing energy efficient windows will make your home more comfortable, dramatically reduce your energy costs and help to create a brighter, cleaner and healthier environment. Windows are possibly the most complex and interesting elements in the fabric of our homes. They provide light and fresh air and offer views that connect our interior living spaces with the great outdoors. However, windows can represent a major source of unwanted heat gain in summer and significant heat loss in winter. Windows can severely impact the heating and cooling loads of a building. Between 46%-61% of a home’s heating energy can be lost and between 79%-86% of its heat gained through windows. Improving their thermal performance increases comfort and reduces energy costs and Australia’s greenhouse gas emissions.
All this is great but what are the benefits of a Thermal Break Frame?
In a nutshell most areas of Australia do not require a thermal break frame, but it's not really that simple. What needs to be considered is the actually SHGC and U-Value (Uw) of the build or quite simply the energy performance of the window.
SHGC (Solar Heat Gain Coefficient) is the measure of the percentage of solar energy that passes through a window. Using a low SHGC system will reduce your cooling loads but will also cut out some solar gain and may therefore increase your heating loads depending on the orientation, shading and climate zone.
The U-Value measures the rate of heat transfer and tells you how well the whole window (Frame +Glass) insulates. The lower the U-Value, the better the window insulates (reduces thermal transfer). And this is where the confusion can start, but I'll leave this part for another Blog!
What are thermal break frames
is probably the first thing that needs to be addressed. Basically a Thermally Broken Frame has a reinforced poly-amide strip or multiple strips depending on the quality of the frame (see pic). The poly-amide strip is a non metallic composite structural material that has a low thermal conductivity which will minimise the transfer of heat and cold from the outside to the inside frame, resulting in improved energy performance.
A thermally broken frame can help improve on performance, but it is the overall performance within certain climate zones that is the question. In a cold climate like Europe it is without question that you would consider using a thermal break frame but in Australia are the benefits the same?
So remember we spoke about energy ratings, the SHGC & U-Value? Well these are what we need to consider and whether spending the extra money is worth it long term.
Thermal Break Frames in a Hot Climate?
In Queensland, which is considered a Hot climate the energy requirements recommended by the local government and AWGA are for a Low SHGC & U-Value, this is because windows need to be able to:
Act as a buffer against the hot air outside, minimising the transfer of heat into a building.
Minimise the loss of cool air from artificial cooling units, reducing the need for cooling.
Reduce or eliminate moisture on the windows (condensation)
However, this has not manifested within the market as architects, assessors and builders are not inspired to do so or obligated to. This is largely due to the fact that most people do not understand the need for double glazed windows with a thermal brake frame in a Hot climate.
Yes thermal break frames in this instance can be beneficial in helping windows to reach Low SHGC values (0.19 -0.27) as well as Low to very low U-Values (1.78 -2.8), which will help with cooling costs as previously mentioned, but remember the frame only plays a minor part in the performance of the window as the total efficiency of the window needs to take into account a larger surface area, that being the glass.
When it comes to the glass and the performance of the window, what type of glass being used is just as import as the frame, if not more so as it not only affects the overall U-Value but also the SHGC, which as stated in a Hot climate should be low. This is were Low E coatings, solar tints, argon or boron gas and other energy efficient elements become important. We recommend talking with one of our experts to get a better understanding on these as there is a lot of information out there that is conflicting and somewhat confusing.
What about Thermal Break Frames in a Cool Climate such as Canberra or Melbourne?
Unlike Queensland the cooler climates are more focused on keeping a home cool in summer but warmer in winter. Although we do not get the -20 degrees Celsius+ the need to keep the homes inside temperature comfortable still requires the right windows. The difference though is that the SHCG is to be higher 0.46 - 0.54 this is to ensure that the thermal performance of the window allows for the inside of the home to use the benefits of the winter sun to warm the house during the day, but you also need to be able to trap this warmth using other thermal benefits such as a "Solar low E*" coatings and exposed concrete slabs etc. With regards to the U-Value it's best to aim lower than 4.2 to get a good performing window. Which in most cases will not require a thermal break frame.
The use of Thermal Frames in Cooler climates can help reduce the transfer of the cold via the frames coming inside the home but as the frames only equate as a small percentage of a window around about 10% or less, the effect on the U-Value in Cooler climates may only change slightly depending once again on the quality of the window, glass and frame. For instance;
Standard 100mm frame Thermally Broken 100mm Frame 6 /12/6 IGU 6/ 12/6 U-Value approx. -3.64 approx. 2.73 SHGC - 0.60 SHGC - 0.38
Standard 100mm frame Thermally Broken 100mm Frame 6 /12Ar/6 Low E 6/ 12Ar/6 Low E U-Value approx. -2.72 approx. 2.32 SHGC - 0.54 SHGC - 0.32
So, looking at these different types of windows it's is possible to see which window could benefit which climate if we are taking into account the energy efficiency of a home, but it's always advisable to talk to us first to assess your build and it's orientation etc. before making a decision.
COST OF THERMALLY BROKEN FRAMES
Depending on who you source your windows from Thermally Broken Frames in Australia can be between 30-100% more expensive than your standard windows. So yes you will be paying a premium but you will need to way up the benefits to you long term based on where you live.
As a guide for a Thermally Broken 100mm frame window with an IGU of 6/12/6 you could expect to pay approximately $860m2 but don't be surprised if some companies want to charge you up $1200m2.
TIP
It is important to note that not all windows are manufactured the same, as residential frames tend to be less robust therefore thinner and in most instances are not even properly sealed between the glass and frame adding to the flow of air through the windows. Always look at the window and make sure that it has a proper structural silicon seal not just a felt or rubber seal- the difference this will make when you stand near your window will be noticeable.
The structural silicon seal will give your window a better wind and water penetration rating of N4 -N6, where a felt or rubber seal will only give you an N2 -N3 rating which is the minimum requirement in some areas of Australia.
Structural Silicon Seal
