Double Glazing vs. Single Glazing. Is the Upgrade Worth It for Australian Homes?

If you’re building or renovating in Melbourne, the question of double glazing will come up eventually. Your builder might raise it, your energy assessor will almost certainly mention it, and you’ll likely see it listed as a premium option when comparing window specifications. But is it actually worth the extra cost for an Australian home?

The answer depends on where you live, how your home is designed, and what you’re trying to achieve. This article breaks down how double glazing works, where it makes a genuine difference, and how to decide whether it’s the right choice for your project.

What Is Single Glazing?

Single glazing refers to a window with one pane of glass. It has been the standard in Australian residential construction for most of the country’s history, and it remains common in many new builds today, particularly in warmer climates where heating loads are low.

A single pane of glass offers minimal resistance to heat transfer. In summer, radiant heat passes through the glass into your home. In winter, warmth generated by your heating system escapes outward through the glass relatively quickly. The glass itself provides some barrier, but not much.

For many years, this wasn’t considered a significant problem in much of Australia. Mild winters in Queensland or the Northern Territory mean the energy penalty of single glazing is modest. In Melbourne and Victoria’s alpine regions, however, the calculus is quite different. Homeowners looking at aluminium windows in Melbourne today are increasingly being asked to consider glazing performance as part of meeting minimum energy standards.

What Is Double Glazing?

Double glazing consists of two panes of glass separated by a gap, typically filled with either air or an inert gas such as argon. The gap acts as a thermal buffer, significantly slowing the transfer of heat between the inside and outside of your home.

The two panes are sealed within an insulated spacer unit, forming what is known as an insulated glass unit or IGU. The performance of a double glazed unit depends on several factors: the width of the gap between the panes, whether the gap is filled with air or gas, the thickness of each pane, and whether any low-emissivity (low-e) coating has been applied to the glass surface.

Low-e coatings are a thin, transparent layer applied to one surface of the glass that reflects radiant heat. In winter, they help keep heat inside the room. In summer, they reduce the amount of solar heat entering through the glass. The combination of double glazing and a low-e coating is now considered best practice for energy-efficient window specification in Victoria.

What Is an Insulated Glass Unit (IGU)?

An insulated glass unit, commonly referred to as an IGU, is the sealed assembly that makes double glazing work. It consists of two or more panes of glass held apart by a spacer bar around the perimeter, with the cavity between the panes hermetically sealed to keep moisture out and the insulating gas in.

The spacer bar is typically made from aluminium or a warm-edge material such as thermoplastic or stainless steel. Warm-edge spacers have lower thermal conductivity than aluminium spacers, which reduces heat loss at the edges of the unit and helps prevent condensation forming around the perimeter of the glass in cold weather. They are generally the preferred choice in high-performance window specifications.

Once assembled, the IGU is a single factory-sealed unit. It cannot be taken apart or repaired in the field. If the seal fails and moisture enters the cavity, the entire unit needs to be replaced. This is why IGU quality and manufacturing standards matter – a well-made unit from a reputable supplier should remain airtight for 20 years or more under normal conditions.

The performance of an IGU depends on several variables working together: the number of panes, the width of the cavity, the type of gas fill (air, argon, or krypton), the glass thickness on each pane, and any coatings applied to the glass surfaces. Argon gas is the most common fill for residential IGUs in Australia. It has lower thermal conductivity than air, which improves the insulating performance of the cavity without significantly increasing cost. Krypton gas offers even better performance but is considerably more expensive and is typically reserved for very narrow cavities or premium passive house specifications.

Low-emissivity (low-e) coatings are applied to one of the inner glass surfaces within the IGU. They reflect long-wave infrared radiation, which means they help keep heat inside during winter and reflect solar heat away during summer. The position of the coating within the unit affects whether it prioritises heating or cooling performance, and your fabricator can advise on the right configuration for your climate zone and window orientation.

How Much Difference Does It Actually Make?

The thermal performance of a window is measured by its U-value and its Solar Heat Gain Coefficient (SHGC). The U-value measures how quickly heat passes through the window overall. The lower the U-value, the better the insulation. The SHGC measures how much solar radiation passes through the glass into the room.

A standard single glazed aluminium window typically has a U-value somewhere around 5.5 to 6.5 W/m²K. A double glazed unit in a standard aluminium frame brings that down to around 3.0 to 3.5 W/m²K. Add a thermally broken frame and argon gas fill, and you can achieve U-values below 2.0 W/m²K, comparable to some European window standards.

In practical terms, a lower U-value means your heating system works less hard to maintain a comfortable temperature in winter, and your cooling system is under less strain in summer. The energy savings compound over the lifetime of the windows, which in a quality aluminium system can be several decades.

CAS’s AluBREAK thermally broken range is designed specifically to work with double glazing, combining an insulated frame profile with high-performance IGUs to achieve strong WERS ratings across both residential and commercial applications.

The Frame Matters as Much as the Glass

One of the most common misunderstandings about double glazing is that the glass does all the work. In reality, the frame plays an equally important role in the overall thermal performance of a window.

Standard aluminium is a highly conductive material. Heat moves through it rapidly, which means that even with double glazed glass, a standard aluminium frame can create a thermal bridge, a path for heat to bypass the insulated glass unit entirely. This is why thermally broken frames exist.

A thermally broken frame incorporates a section of low-conductivity material, typically a polyamide strip, within the aluminium profile. This breaks the conductive path through the frame and significantly improves the whole-of-window U-value. If you’re investing in double glazing, pairing it with a thermally broken frame gives you the full benefit of the upgrade.

The AluBREAK residential thermally broken windows and commercial thermally broken doors and windows from Concept Aluminium Systems are available in awning, sliding, stacker, and hinge door configurations, making them suitable for most residential and commercial applications.

Is Double Glazing Worth It in Melbourne’s Climate?

Melbourne sits in climate zone 6 under the NatHERS climate zone classification, which is characterised by cool winters and warm summers. It’s one of the Australian climate zones where double glazing delivers a clear and measurable benefit.

The Victorian Government’s energy efficiency requirements for new homes have become increasingly stringent, and from October 2023, new residential builds in Victoria must achieve a minimum 7-star NatHERS rating. Windows are a significant variable in achieving that target. An energy assessor will model the performance of your window specifications as part of the NatHERS assessment, and upgrading from single to double glazing can meaningfully improve your star rating, sometimes enough to avoid more disruptive or expensive changes elsewhere in the design.

Sustainability Victoria notes that double glazed windows can reduce heat loss through windows by up to 50 per cent compared to single glazing. For a home with a significant glazed area, that’s a material reduction in heating and cooling load.

If you’re in a regional Victorian location such as Ballarat, Bendigo, or the Dandenong Ranges, the case for double glazing is even stronger. These areas experience colder winters than metropolitan Melbourne, and the energy savings from double glazing accumulate faster.

Where Double Glazing Makes Less Sense

Not every situation calls for double glazing. In warmer parts of Australia, such as Brisbane, Darwin, or coastal Queensland, heating loads are minimal and the payback period for the additional cost of double glazing can stretch out considerably. In these climates, shading, ventilation, and glass selection often deliver more value than doubling the pane count.

Even within Victoria, a small holiday home or a well-shaded north-facing renovation with limited glazed area may not benefit enough from double glazing to justify the cost difference over single glazing with a quality low-e coating.

The key is to look at your specific project in context. An energy assessor or experienced window supplier can model the performance difference for your home’s orientation, size, and glazed area, giving you a clearer picture of whether the upgrade stacks up financially.

Acoustic Performance: A Secondary Benefit

Thermal insulation tends to get most of the attention in the double glazing conversation, but acoustic performance is worth considering, particularly for homes near busy roads, flight paths, or commercial areas.

Two panes of glass separated by a gap are significantly better at attenuating airborne sound than a single pane. The performance depends on the glass thicknesses used and the width of the gap, and specialist acoustic glazing uses asymmetric pane thicknesses to target a wider range of frequencies. For homes in noise-sensitive locations, the acoustic benefit of double glazing can be as compelling as the thermal one. This consideration applies equally to commercial window systems in offices, apartments, and mixed-use buildings, where acoustic performance is often a core specification requirement.

What About Condensation?

One of the more visible signs of a thermally poor window is condensation forming on the interior glass surface in cold weather. This happens when the glass surface temperature drops below the dew point of the interior air, causing moisture to condense on the cold surface.

Double glazing keeps the inner pane warmer in cold conditions because the outer pane absorbs the cold and the gap provides insulation. As a result, condensation on the interior surface is significantly reduced compared to single glazing. This matters not just for comfort but for building health, as persistent condensation on window surfaces can contribute to mould growth in the surrounding frames and wall cavities.

How to Compare Your Options Using WERS Ratings

The Window Energy Rating Scheme (WERS) provides standardised energy ratings for window products across Australian climate zones. WERS ratings allow you to compare the thermal performance of different window configurations in a consistent way, factoring in frame type, glazing, and orientation.

CAS windows carry WERS ratings across their product ranges, which makes it straightforward to compare single and double glazed configurations for your specific climate zone and orientation. You can find WERS rating information on the Concept Aluminium Systems WERS ratings page.

When reviewing WERS data, look at the rating for your climate zone and your window orientation. A window rated for heating performance in a south-facing position will have a different rating to the same window facing north, where solar gain becomes an asset in winter rather than a liability.

Working Out the Cost Difference

Double glazing typically adds a meaningful cost premium over single glazing, and the exact figure varies by frame system, glass specification, and project size. For a full house of windows and doors, the additional cost can range from several thousand dollars to significantly more, depending on the scale and specification.

Whether that cost is worth it depends on how long you plan to stay in the home, your heating and cooling costs, and what value you place on comfort independent of energy savings. A well-insulated home is simply more comfortable to live in, with fewer cold spots near windows in winter and less radiant heat gain in summer.

Your builder or fabricator can provide a detailed quote for both single and double glazed configurations, making it easier to weigh the cost difference against the projected benefits. If you’re working with an energy assessor on a NatHERS rating, ask them to model both scenarios so you have comparable data to inform your decision.

Talking to a Fabricator

The best way to work through the double glazing question for your specific project is to speak with a fabricator who knows the product range and can advise on performance, cost, and lead times.

Concept Aluminium Systems has a Find a Fabricator tool that connects you with local fabricators across Victoria and beyond who work with CAS window systems. You can also visit one of the CAS showrooms to see the window systems in person and ask questions about the glazing options available across the residential aluminium windows and commercial aluminium windows ranges, as well as the thermally broken options.

Ready to discuss your project? Contact us today and let us know your requirements.

This article is intended as general guidance for homeowners and builders. Window and glazing selection should be considered alongside your specific site conditions, climate zone, and energy requirements. We recommend consulting with a qualified fabricator, builder, or energy assessor for advice specific to your project.

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