uPVC or thermally broken aluminium windows: an honest Melbourne comparison

If you are buying windows in Melbourne, you will find that most of the comparison pages are written by someone who sells uPVC. We fit aluminium. That is a bias too, so here is the comparison with the bias declared, and with the point uPVC sellers get right stated first.

Also compare opening style, size, glazing, seals and installation.

Where uPVC is ahead

A standard aluminium frame is a poor insulator. Sanctuary magazine, published by the not-for-profit ReNew, puts it bluntly: "aluminium is a great conductor of heat and so provides no insulation" (Sanctuary). A uPVC frame holds heat better than a standard aluminium one. If a bedroom window is cold and the frame is the weak link, uPVC is a fair choice for that window, and we would rather say so than pretend otherwise.

What a thermal break changes

A thermally broken aluminium frame uses separate inner and outer aluminium sections joined by a low-conductivity structural material. This reduces conduction through the frame. Performance still depends on the exact frame, glass and window configuration, so ask for the whole-window rating for the product quoted (Your Home).

A standard profile has a continuous metal connection. In the thermally broken construction, low-conductivity structural bridges join separate metal sections. From 3–6 seconds the bridges move into position for explanation; from 6–12 seconds the markers illustrate indoor-to-outdoor heat flow in winter. Heat can still pass through both profiles. Marker speed is not a measured heat-flow rate. These simplified profiles are not installation details.

uPVC can also provide strong thermal performance. Compare the exact products rather than assuming the frame material determines the result.

Where aluminium suits

Aluminium systems can provide slim sightlines and suit large glazed openings. Check the quoted system’s permitted panel sizes, glass weight and performance ratings. A thermally broken aluminium option may suit a wide sliding or stacking door, while a well-specified uPVC system can also provide strong thermal performance. If you already have aluminium frames and the question is whether to keep them, see can you double glaze existing aluminium windows.

Compare the whole window, not the frame

This is the single most useful thing in this post. A window's performance comes from the frame and the glass together. Sanctuary explains that the Window Energy Rating Scheme (WERS) gives "comparative ratings for frames and glass combined in a functioning window or door", with star ratings based on the window's U-value and solar heat gain coefficient (SHGC), for heating and cooling across three climate types (Sanctuary).

In practice:

1. Ask for the whole-window U-value for the exact frame and glass in the quote. The lower the U-value, the better the window resists heat flow.
2. Ask for the SHGC as well. It tells you how much solar heat comes through. Lower solar gain can help exposed western glazing, while useful winter sun may call for a different specification. Consider orientation and shading; lower SHGC is not universally better.
3. Be careful with frame-only tables. A frame figure is not a window figure, and two sellers quoting different kinds of number are not comparing the same thing.
4. Ask for the rating on the product quoted, not on a similar one.

AGWA/WERS confirms that these are whole-window values. Ask for the rating of the exact system being quoted, rather than treating an illustrative U-value range as a product limit.

A few honest limits

We have not published a U-value for our windows, and we are not going to quote lifespan claims for either material, because we did not find independent durability data that we trust. If a supplier gives you a durability figure, ask where it comes from.

Both the glazing and frame affect whole-window performance. Installation and air leakage also matter. A double-glazed unit with the right glass type can improve a window in ways a frame choice cannot, which is the point of our quieter and warmer windows guide. And a frame does not fix a draughty install, so fit matters as much as the material.

So which should you choose?

Choose by the opening and the quoted system. uPVC is a fair option where insulation is a priority. Thermally broken aluminium may suit large sliding or stacking doors and slim sightlines. Check permitted sizes and performance for either material, get the whole-window rating in writing and compare like with like.

For what these jobs typically cost in Melbourne and what moves the price, see our double glazing cost guide. If you are weighing up a discount, our rebates guide covers what the Victorian Energy Upgrades program does and does not cover.

Our double glazing and sliding doors page covers the aluminium options we work with and how we quote.

Considering aluminium windows or sliding doors? Send us photos and approximate opening sizes to discuss the available options and request a written quote.