Thermally Broken Windows in Melbourne — When They're Worth It
"Thermally broken" is the most oversold phrase in aluminium windows. We hold certified WERS ratings for our thermally broken and standard systems with identical glass in both, so this page can do something most can't: show you exactly what the break is worth, window type by window type — including where it's worth almost nothing.
What does "thermally broken" actually mean?
Aluminium is a superb conductor of heat, which is exactly what you don't want in a window frame. On a cold Melbourne morning a standard aluminium frame carries warmth straight from the inside face of the window to the outside face, and the frame is a big enough share of the opening that it drags down the performance of whatever glass you put in it.
A thermally broken frame solves that by splitting the section into an inner and an outer half joined by a low-conductivity insulating barrier — the "break". Heat has to cross that barrier instead of running through solid metal.
The effect is measurable, not marketing. Holding the glass identical and changing only the frame, our 50mm thermally broken awning comes in a full 1.0 to 1.1 lower on whole-window U-value than our standard Comet awning.
How much better is a thermally broken window than a standard aluminium one?
Here's the honest comparison, holding the glass constant and changing only the frame.
Take a 5mm clear / 12mm argon / 5mm Low-E Plus double glazed unit. In our Comet awning that window is certified at a whole-window U-value of 3.2, SHGC 0.45, rating 6.1 heating and 3.5 cooling stars. Put the identical unit in our 50mm thermally broken awning and it comes in at 2.1, SHGC 0.42, rating 6.9 heating and 4.2 cooling stars.
That pattern holds right across the range. Comparing the two systems across the 24 glazing make-ups they both offer, the thermally broken frame improves the U-value by 1.0 to 1.1 every single time — a reduction of between a quarter and a third, achieved by the frame alone with the glass unchanged.
| Same glazing unit | Standard frame | Thermally broken frame | Improvement |
|---|---|---|---|
| 5mm clear / 12mm argon / 5mm Low-E Plus — awning | Comet awning, Uw 3.2 | 50mm TB awning, Uw 2.1 | 1.1 |
| 5mm clear / 12mm argon / 5mm Low-E Plus — fixed | Comet fixed, Uw 2.2 | 50mm TB fixed, Uw 1.7 | 0.5 |
| 6mm clear / 12mm argon / 6mm clear — hinged door | Entry door, Uw 3.9 | 10755 TB open-in door, Uw 3.0 | 0.9 |
| 5mm Low-E Eco / 12mm argon / 5mm clear — commercial awning | 10055 CG awning, Uw 4.3 | 160mm TB awning, Uw 3.2 | 1.1 |
Certified WERS whole-window U-values. Each row holds the glazing make-up constant and changes only the frame.
Does it help as much on a fixed window as an opening one?
No, and this is the most useful thing we can tell you about where to spend the money.
A fixed lite has far less frame and no sash, so there's less aluminium to conduct heat in the first place — which means there's less for a thermal break to fix. On the same 5mm clear / 12mm argon / 5mm Low-E Plus unit, our Comet fixed window is certified at a U-value of 2.2 and our 50mm thermally broken fixed window at 1.7. That's a 0.5 improvement.
The same glass in an awning gains 1.1, going from 3.2 to 2.1. So the thermal break earns roughly twice as much on an opening sash as it does on a fixed lite. If you're going thermally broken selectively, the awnings and doors are where it pays.
Is a thermally broken window always better than a standard one?
No — and we'd rather tell you that than sell you one that doesn't earn its place.
Our 160mm thermally broken awning is a heavy architectural section, and against a plain 5mm/12mm argon/5mm clear unit it is certified at a U-value of 3.8 where our standard Comet awning with the identical unit is 4.0. Across the 27 glazing make-ups the two share, the 160mm thermally broken system beats the Comet by between 0.0 and 0.2. That is effectively nothing.
The reason is that WERS rates the whole window, frame and glass together. A deeper, wider frame means more frame area and less glass area, and that penalty eats most of what the thermal break delivers. Compared against systems in its own weight class the same 160mm frame does very well. Compared against a good residential frame, it doesn't. Judge by the certified whole-window number for your actual configuration, never by the words "thermally broken".
Is a thermally broken window worth it for a Melbourne house?
In our experience most Melbourne homes reach their energy target without going thermally broken — a good Low-E double glazed unit in a standard frame does the job on a typical project. So our honest default is: not usually, and we'll tell you when it isn't.
Where it does earn its place is specific. When your energy report sets a U-value no standard system can reach, thermally broken is the step that gets you there. When a room is mostly glass — a big north or west elevation, a rear extension opening onto a deck — the frame is a large share of the wall and the break matters more. And when comfort right at the window matters, warmer frame surfaces are noticeable on a cold morning in a way an averaged rating doesn't capture.
Typical guidance only — we'd confirm against your specific report and schedule.
Should I use thermally broken windows throughout, or just on some?
Selectively, in most cases, and our own data tells you where to put them.
The thermal break earns roughly twice as much on an opening sash as on a fixed lite — 1.1 on a Comet-versus-thermally-broken awning against 0.5 on the equivalent fixed windows. It earns 0.7 to 0.9 on a hinged door. So the awnings, casements and doors are where the money works hardest, and a large fixed picture window is where a standard frame with a good double glazed unit gets closest to the thermally broken result on its own.
The other input is your energy report. If it sets targets per item, only the items that miss need the step up. We'd rather work through your schedule window by window than apply one specification across the job.
My energy report wants a U-value my windows can't reach — what are my options?
We work up the ladder rather than jumping to the most expensive answer. For each item we take the required U-value and SHGC from your report and look for the most economical certified combination that meets both: clear single glazing first, then Low-E single, then double glazing, then a better Low-E double glazed unit, then a warm-edge spacer. Stepping the item up to a thermally broken system is the last move, made when nothing in a standard system reaches the target.
Two options people forget sit before that step. Changing the window type is often cheaper and more effective than changing the frame — a fixed lite beats any operable window in the same range. And targets are usually per item, so it's frequently one or two windows that need the step up, not the whole house.
What's the lowest U-value you can actually achieve?
The lowest certified whole-window U-value we can supply is 1.4, on our 50mm thermally broken fixed window with a 4mm LightBridge / 12mm 90 per cent argon / 4mm ClearEnergyTech double glazed unit on a warm-edge spacer. That configuration also gives an SHGC of 0.47 and visible transmittance of 0.64, rating 6.3 heating and 4.2 cooling stars.
The same unit in our 50mm thermally broken awning gives 1.8, in our 10755 thermally broken open-in hinged door 2.1, and in the open-out door 2.3.
Two things worth saying plainly. That is a best case, not a typical one — it needs the thermal break, a high-performance double glazed unit and the warm-edge spacer all together. And no standard-framed system we build carries that same glazing make-up, so we can't offer you a like-for-like against it.
Can I get thermally broken windows single glazed?
No, and there'd be no point. Every one of the 272 certified residential energy ratings we hold for our thermally broken systems is double glazed — there is not one single-glazed row among them, and the same is true across all 523 commercial rows. Our glazing documentation backs that up: every glazing option for these systems is a double glazed or insulated glass unit.
That's deliberate. A thermal break stops heat crossing the frame, but if the glass beside it is a single pane you've fixed the small problem and left the large one. The two upgrades work together, which is why the system is only built one way.
Will thermally broken windows stop condensation?
They help, sometimes a lot, but nobody should promise you they'll stop it — and the industry guidance is clear about why.
Condensation forms when warm humid indoor air meets a surface cold enough to hit dew point. The industry position, which matches ours, is that condensation is usually driven by high humidity and poor ventilation in the room rather than by a fault in the window. What a better window does is raise the temperature of the surfaces you see, so they stay above dew point more of the time — and thermally efficient frames, thermally broken aluminium among them, are named alongside double glazing as the things that achieve that. Single glazing is the specification to avoid.
So: thermally broken framing plus a good double glazed unit plus a warm-edge spacer gives you the best surface temperatures we can supply. Extraction fans, drying clothes outside and ventilation still do their share.
Are thermally broken frames weaker than solid aluminium ones?
Not on the evidence we hold. Our thermally broken open-out hinged door tested to N5 in the general position and N4 in corners, with 3000 Pa ultimate pressure — the strongest residential result in any system we supply, thermally broken or not. Our thermally broken awning over fixed tested N4 general and N3 corner at 2000 Pa ultimate — matching the N4 general class our standard Comet, Apollo and Titan awnings achieve.
Two caveats we'd rather state than have you discover. Several of our thermally broken test reports record an ultimate pressure but no wind class at all — those systems have no verified rating and we don't claim one. And each configuration is tested as its own assembly, so a rating never carries across from one thermally broken system to another.
Are thermally broken windows quieter?
There's a modest gain, and it comes from the glass rather than the break.
For our 10755 thermally broken system we hold simulated acoustic results: the awning models at Rw 30 with a 4-12-4 unit, Rw 31 with 6-12-6, and up to Rw 36 with a 6-12-6.5 acoustic laminate. The thermally broken sliding door models one point lower across the same set, Rw 29 to 35.
Two things to be straight about. Those are simulations, not laboratory tests — the reports say plainly that modelling can't guarantee in-practice performance and shouldn't be used directly for detailed design, so we wouldn't rely on them for an acoustic compliance requirement. And no acoustic figures are published at all for our other thermally broken systems. If noise is the problem, an acoustic laminate is the specification that moves the number, not the frame.
Which of your window and door systems are thermally broken?
We build three thermally broken families.
Our 50mm residential thermally broken range covers fixed lites and awning sashes, plus casement sashes, awning-over-awning and high-lite and down-lite arrangements, transoms and mullions. It's the residential option and it holds the best energy figures we can supply.
Our 10755 thermally broken system is the broadest — fixed lites, awnings, casements, sliding doors, stacker doors, open-in and open-out hinged doors, French doors, bi-fold sliding doors and curtain wall.
Our 160mm thermally broken system is the heavy architectural one — fixed lites, awnings, hinged and French doors and stacker doors, including bi-parting stackers.
Which one suits depends on the opening, the target U-value and whether the job is residential or architectural. We'd work that through against your energy report.