Thermally Broken Windows vs Non-Thermally Broken Windows
Most homeowners building or renovating spend a lot of time picking the right glass, the right style, and the right colour for their windows. The frame construction usually gets less attention. But the frame has a direct effect on how comfortable your home feels, what you pay on energy bills, and whether condensation and mould become a problem down the track.
Two types of aluminium frames are used in Australian homes: thermally broken and non-thermally broken. They can look very similar from the outside. The difference is in how they’re built, and that difference has a real impact on day-to-day living. This post explains both clearly so you know what to look for before you buy.
What Are Thermally Broken Windows?
Aluminium conducts heat easily. In a standard aluminium frame, the metal runs from the outer face to the inner face without any interruption. Heat from outside moves straight through the metal and into your room. In summer that pushes indoor temperatures up. In winter it lets warmth out.
A thermally broken frame addresses this by placing a non-conductive strip, usually made from polyamide plastic, between the outer and inner sections of the aluminium. The two metal sections are separated and no longer in direct contact. Heat cannot travel as freely through the frame, so your indoor temperature stays more stable and your heating or cooling system doesn’t need to work as hard to maintain it.
What thermally broken frames do for your home
- Keep indoor temperatures more stable without constant heating or cooling
- Significantly reduce condensation on the inside of window frames
- Lower energy bills over time
- Reduce the chance of mould forming near windows and sills
- Perform well in both hot summers and cold winters
- Meet the energy efficiency requirements for modern Australian homes
- Suitable for Passive House certification and high NatHERS star ratings
What Are Non-Thermally Broken Windows?
Non-thermally broken frames are made from a single, continuous piece of aluminium running from the outer face to the inner face. There is no barrier in the middle. Heat passes through the metal freely in both directions.
These frames have been common in Australian homes for a long time. They cost less to manufacture and are easy to source. For internal windows or partitions that don’t face outside, they’re generally fine. For any external window or door, the absence of a thermal barrier leads to real problems with heat, condensation, and maintenance that tend to compound over the years.
What non-thermally broken frames mean in practice
- The frame reaches outdoor temperatures in winter and summer
- Condensation forms on the inside face of the frame in cool or humid conditions
- That moisture encourages mould on sills and nearby walls
- Rooms near these windows feel less comfortable year-round
- Energy bills tend to run higher because heating and cooling have to work harder
- These frames generally fall short of the energy standards required in modern builds
Differences Between Thermally Broken and Non-Thermally Broken Windows
How the frame is built
A thermally broken frame has two separate aluminium sections with a plastic insulating strip sitting between them. A non-thermally broken frame is one solid piece of aluminium with nothing in the middle.
That one structural difference is what drives every performance gap between the two. The insulating strip blocks the direct heat path through the frame. Without it, the aluminium carries heat from the warmer side to the cooler side without any resistance.
Heat coming in and going out
In a non-thermally broken frame, summer heat outside transfers inward through the metal. The air conditioner has to work against that constant heat input to keep the room cool. In winter, warmth from inside the home escapes outward through the same path. The heater runs longer to compensate.
Thermally broken frames reduce both. The polyamide strip slows heat movement in either direction. The home holds its temperature better, and heating and cooling run less frequently. Double glazing improves how the glass performs but doesn’t change the frame. Both a thermally broken frame and quality glazing are needed to get the full performance benefit from a window installation.
Condensation and mould
Condensation on window frames is one of the most common complaints from homeowners with standard aluminium windows. In cooler weather, the inside face of a non-thermally broken frame gets cold because it’s directly connected to the outdoor temperature. When warm air inside the home contacts that cold surface, moisture forms on it. Water streaks appear on the frame and collect on the sill.
Over time, that moisture creates conditions for mould. It affects paint on surrounding walls, deteriorates the sill, and in more serious cases gets into wall cavities where it’s harder to detect and fix. Thermally broken frames stay warmer on the inside face because the break limits how much cold comes through. Condensation is much less likely to occur, and the mould risk that comes with it is substantially reduced.
Frame lifespan and durability
Standard aluminium frames are slim and light. Ongoing moisture from condensation takes a toll on them over the years. It causes gradual surface deterioration and can affect the plaster and timber in the surrounding wall.
Thermally broken frames are slightly deeper due to the insulating strip, which also adds structural strength. Because condensation is less likely to form, the frame and the materials around it are exposed to far less moisture over time. For a home built to last decades, that matters when it comes to long-term maintenance costs.
Energy ratings and running costs
U-values measure how well a window resists heat passing through it. A lower number means better insulation. Three U-values come up when comparing windows:
- Ug value: How well the glass insulates on its own
- Uf value: How well the frame insulates on its own
- Uw value: How well the whole window, glass and frame combined, insulates
The Uw value is what counts for your home’s energy performance and NatHERS compliance. Some suppliers quote only the Ug value because it’s a smaller number and looks better in a brochure. But it only reflects the glass. A standard aluminium frame with a poor Uf value pulls the overall Uw well above what the glass figure suggests.
Thermally broken frames have much lower Uf values, keeping the combined Uw value down. For homes targeting a 7-star NatHERS rating or above, non-thermally broken frames generally can’t meet the threshold regardless of the glazing specified.
Noise reduction
The plastic insulating strip inside a thermally broken frame absorbs sound vibration slightly better than solid aluminium. It’s not the main reason to choose thermally broken frames, but it does contribute to a quieter indoor environment, particularly when paired with double glazing.
Non-thermally broken frames provide no equivalent benefit. Sound vibration travels through the continuous metal without interruption.
Thermally Broken vs Non-Thermally Broken: At a Glance
| Feature | Thermally Broken | Non-Thermally Broken |
| Frame construction | Two aluminium sections with insulating strip | Single continuous aluminium piece |
| Heat transfer through frame | Significantly reduced | High |
| Condensation on inside of frame | Unlikely | Common in cool or humid weather |
| Frame U-value (Uf) | 1.0 to 2.5 W/m²K (typical) | 4.0 to 7.0 W/m²K (typical) |
| Works well with double glazing | Yes | Can hold units but frame limits the overall result |
| Mould risk near windows | Low | Moderate to high |
| Frame durability over time | Good | Reduced in humid conditions |
| Suitable for 7-star NatHERS homes | Yes | Generally no |
| Passive House compatible | Yes | No |
| Noise reduction | Modest benefit | None |
| Upfront cost | Higher | Lower |
| Long-term energy savings | Yes | Minimal |
| Works in all Australian climates | Yes | No |
When to Choose Thermally Broken Windows
For most Australian homeowners, thermally broken frames are the right choice for any window or door that faces outside. A few situations where they become particularly necessary:
- Your home gets very hot in summer: If air conditioning runs most of summer, non-thermally broken frames are part of the problem. The metal conducts outdoor heat inward and the cooling system has to work against a constant heat source. Thermally broken frames reduce that heat transfer and ease the load on the air conditioner.Thermally broken aluminium windows are built to handle Australian summer heat without the frame becoming a liability.
- You live near the coast or in a humid area: Coastal homes deal with high humidity throughout the year. Standard aluminium frames in these conditions are consistently prone to condensation on the interior surface. Thermally broken frames stay warmer inside, so moisture doesn’t settle on the frame and cause damage to the frame, sills, and nearby walls.
- Your winters are cold: In parts of Victoria, Tasmania, the ACT, and much of inland New South Wales, winters are cold enough that non-thermally broken frames become a real problem. Interior condensation forms regularly, heat escapes through the metal constantly, and the impact on comfort and running costs is significant. Thermally broken frames limit heat loss and keep condensation from forming.
- You’re building to a high energy standard: Homes aiming for 7-star NatHERS ratings or Passive House certification generally need thermally broken frames to reach those targets. Non-thermally broken frames can’t achieve the U-values these standards require, regardless of the glazing used.
- You have large windows or sliding doors: Larger glazed areas have a bigger influence on indoor comfort than smaller windows. The minimal sliding door systems in thermally broken aluminium are designed for large openings, keeping sightlines slim while maintaining solid thermal performance.
- You’re replacing windows during a renovation: If existing windows are causing condensation, cold spots near the glass, or higher-than-expected energy bills, replacing them with thermally broken frames makes a noticeable difference. The tilt and turn window range in thermally broken aluminium suits renovations where a clean perimeter seal and good thermal performance are both priorities.
A Decision That Pays Off Over Time
Thermally broken windows cost more upfront than standard aluminium frames. That’s a genuine factor, and it’s reasonable to weigh it carefully. The gap closes over time through lower energy bills, reduced condensation damage, and better frame durability. For a home intended to last twenty years or more, the cost over that full period generally works in favour of thermally broken frames.
Standard aluminium frames were an accepted choice when energy costs were lower and performance expectations less demanding. Both have shifted. Australian homes are now built to higher standards, and homeowners reasonably expect to stay comfortable without heating or cooling systems running at full capacity year-round.
For homeowners planning a new build or renovation, Thermal Facade Solutions works with architects, builders, and homeowners across Australia on custom thermally broken window and door systems. Get in touch to talk through what suits your project.
