The walls in a brand new Brisbane home tend to let the heat right on out & glass is even worse, it just lets solar radiation right on through, transmitting it more strongly than any other building material used in your average residential construction project. Single pane windows in places with a subtropical climate aren’t going to slow down heat transfer at all, they’re more like a superhighway for the heat. The sealed space in a double-glazed unit flips this whole dynamic on its head by introducing a barrier between the indoors and the outdoors.
The sealed unit is known as an Insulated Glass Unit, or IGU, for short. There are usually two panes of glass separated by a gap, anything from 6 to 20 millimetres wide, and this gap is usually filled with either dried-out air or argon gas. Now argon is the preferred choice because it’s a lot denser, slowing down the movement of heat within the gap and making it a more effective barrier to heat transfer compared to just air on its own. As a result you get a U-value, which is a measure of how quickly heat moves through a unit, that can go from around 6.2 W/m²K for a single pane of clear glass right down to under 2.0 W/m²K for a decent double glazed windows Brisbane.
- Glass lets solar radiation pass through more than any other building material used in regular homes.
- LowE coatings will reflect infrared heat back out into the street in the summer without blocking the view.
- The main concern when it comes to keeping your Brisbane house cool is how the windows will perform in the summer, not keeping warm in winter.
Not All Double Glazing Is Cut from The Same Cloth, Brisbane Needs A Specific Spec
A window that does an okay job in Melbourne might not even come close to doing as good a job in Brisbane. Melbourne’s glass priorities are all about keeping the warmth in during winter, but it’s the other way round in Brisbane where the main priority is keeping the heat out of the sun. It makes a big difference when you’re reading through product specs, a standard double-glazed unit without a LowE coating is still going to let a heap of heat in through the glass.
The Window Energy Rating Scheme, or WERS for short, is Australia’s national window rating system. Products get their own star ratings for heating & cooling performance, and for Brisbane’s subtropical Climate Zone 2 the target spec is a 5 to 6 star cooling rating. If you’ve got windows that face west or north and get direct afternoon sun then you need to go for solar control glass that’s got a lower Solar Heat Gain Coefficient (SHGC) than standard LowE glass, so less heat enters the home.
When talking to suppliers its a good idea to ask about both the U-value and the SHGC for double glazed windows Brisbane rather than just relying on a general star rating, which gives you a better idea of how well a unit will actually perform over the whole cooling season.
What Different Frame Materials Mean for Brisbane’s Climate?
Frame choice really matters when it comes to the performance of your window system, but in a place like Brisbane, the glass you choose is what’s going to make the biggest difference. That being said, the frame you pick can make a difference when it comes to how long it lasts, how much maintenance it needs, and whether you get any thermal bridging going on.
- Aluminium Frames: They’re a cost-effective option and pretty durable, but the problem is, they conduct heat like crazy, which can kind of cancel out the insulating glass unit.
- uPVC Frames: These have a really strong thermal barrier, won’t rust in the coastal or subtropical conditions so common in Brisbane, and they’re actually the preferred choice for a lot of people around here.
- Timber Frames: These have the highest insulation value of all three, but you have to keep them well maintained if you’re going to get the best out of them in this kind of climate.
Cost comparison per square metre:
- Aluminium: $300 to $1,250
- uPVC: $300 to $500
- Timber: $600 to $1,500
One thing that definitely gives uPVC the edge over aluminium in places like this is that it won’t rust near the bay and coastal suburbs. Plus frame thermal bridging can really bring down the overall performance of your window system, especially if you’re using standard aluminium profiles. That’s not to say that thermally broken aluminium is a total waste of time, it does help, but doesn’t quite bridge the gap (no pun intended) entirely. For most people in Brisbane, uPVC is the way to go when you consider the combination of durability & thermal performance & cost.
What the Numbers Add Up To for a Full Home Upgrade?
Installing double-glazed windows in a whole house in Brisbane tends to cost somewhere between $2,000 and $3,500 per typical opening, and the per square metre price point can be as low as $1,050 or as high as $2,100 for standard to acoustic grade specifications. A 3-bedroom home full of double glazing is likely to cost between $20,000 and $32,000, 4 bedrooms, you’re probably looking at $30,000 to $45,000. And if you’ve got a 2-storey house that needs scaffolding or any other special accessories, it can get a lot more complicated and the cost can add up quickly.
If you do the maths, though, most people see a 20 to30% drop in energy costs after putting in double-glazed windows. And over a 5 to 10 year payback window, against the fact that the units are likely to last for more than 25 years, the outlay starts to look a lot more reasonable.
The Noise Question: How to Block Out Brisbane’s Traffic?
Acoustic performance, or how well your windows block out noise, is a secondary benefit of double glazing that people around here often like to focus on. The sealed space between the two panes of glass can really reduce how much of the world’s noise gets in through the windows, making it a real advantage for people who live near the Pacific Motorway, or the Gateway Motorway, or anywhere else that’s really busy.
If you want to get really serious about noise reduction, acoustic laminated glass is the way to go, it includes an extra layer of material sandwiched in between the glass that can cut down on even more of the background noise. People who live near flight paths or freight roads might actually find that the acoustic benefits of double-glazed windows are almost as important as the thermal ones, making it a solution to two problems with just one investment.
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