Key Takeaways
- The difference: in single glazing vs double glazing, single is one pane of glass and double seals two panes around an insulating gap.
- Performance: double glazing typically reduces heat loss or gain by 75% to 80% compared with single glazing.
- The frame counts: an aluminium frame conducts heat while a uPVC frame insulates, so the glass and frame work as a pair.
- Cost: standard installed uPVC double glazed windows in Melbourne cost about $1,700 to $3,600 per opening.
Windows can be a major source of unwanted heat gain in summer and significant heat loss in winter, according to the Australian Glass and Window Association. That is why the choice between single and double glazing shapes your comfort all year. This guide explains how each works, how they compare and what to check before you buy.
What Is the Difference Between Single and Double Glazing?
The difference is the number of glass panes. Single glazing is one pane of glass set in a frame, and it has long been the standard in Australia. Double glazing, as used in our double glazed windows, joins two panes in a sealed unit. The gap between them adds insulation that single glazing lacks.
The sealed gap slows heat transfer in three ways:
- Conduction: heat moving directly through a material. Trapped air or gas resists it far better than solid glass.
- Convection: heat carried by circulating air. The narrow, sealed gap stops the gas moving freely.
- Radiation: heat transferred as radiant energy. Coatings on the glass can reflect it back into the room.
A single pane offers almost no insulation, so heat passes through the glass easily. Because heat only ever moves from hot to cold, double glazing works in both directions. It keeps warmth in during winter and keeps outside heat out during summer.
Single Glazing vs Double Glazing Compared
Double glazing outperforms single glazing on insulation, condensation and noise, but it costs more upfront. This table shows where the two differ most.
| Feature | Single Glazing | Double Glazing |
|---|---|---|
| Construction | One pane of glass in the frame | Two panes joined by a spacer in a sealed unit |
| Insulation | Almost none | Sealed gap slows heat moving in and out |
| Gas fill | None | Argon in every Ultimate Windows unit |
| Condensation | Cold inside surface collects moisture | Warmer inside surface, especially with a uPVC frame |
| Noise | Little reduction | The gap helps muffle traffic and outside noise |
| Upfront cost | Lower | Higher, but it pays back in comfort |
Double glazing typically reduces heat loss or gain by 75% to 80% compared with single glazing. The exact result depends on the glass, the frame and the quality of the installation, so it pays to specify the whole window rather than the glass alone.
What Is IGU Glass (Insulating Glass Unit)?
IGU stands for insulating glass unit, which is the sealed double glazed unit that sits inside the window frame. It is the part that does the insulating, and it is made up of four elements.
- Glass panes: two panes that can carry different coatings to suit the needs of a project.
- Spacer: the strip that holds the panes apart. Standard aluminium spacers conduct heat and can create cold spots, so our pane spacers are not made of metal.
- Sealed gap: filled with argon, which is denser than air and insulates better.
- Low-E coating: a microscopic, transparent coating that reflects radiant heat while still letting natural light through.
At Ultimate Windows, double glazing is the minimum standard in every window we make. Argon gas is included in all our glass at no extra cost.
Why the Frame Matters as Much as the Glass
A double glazed unit only performs as well as the frame that holds it. Aluminium conducts heat readily, so an aluminium frame can undercut the glass unless it is thermally broken. uPVC is a low-conductivity material that insulates as standard.
- Aluminium: durable and lightweight, but the frame carries outside temperatures to the inside surface.
- Timber: performs well thermally but needs more ongoing maintenance.
- uPVC: a multi-chambered, low-conductivity frame that needs little more than a wipe with soapy water.
Most Australian windows are single glazed with aluminium frames. In winter that combination creates a cold surface inside the home, and warm, moist air turns to condensation when it meets it. Our uPVC frames are made to order in our Wodonga factory and designed specifically for double glazing.
Is Double Glazing Worth It Over Single Glazing?
For most homeowners replacing windows, yes. Double glazing improves comfort and reduces outside noise, and it can lower heating and cooling use, although savings vary with your home, climate and current windows. The upfront cost is higher than single glazing, so it helps to see real numbers first.
- Price: standard installed uPVC double glazed windows in Melbourne cost about $1,700 to $3,600 per opening, including removal of your old windows. Our guide to how much double glazing costs in Melbourne breaks that down by window type.
- Third pane: if you are weighing up triple glazing as well, read our comparison of double glazing vs triple glazing.
- Guarantee: we back every window with a 12-year guarantee, against the 5 years the Australian Window Association recommends.
How to Check Whether Your Double Glazing Is Working
Where moisture forms tells you what is happening. Work through these steps:
- Look outside first: condensation on the outside of the glass or frame is fine, because the water is where it should be.
- Check the inside surface: condensation here means the glass or frame is colder than the room air, so outside cold is travelling through, often via an aluminium frame.
- Look between the panes: moisture inside the sealed unit means the seal has failed and the unit needs replacing. A glazier can usually sort this out.
- Ask about installation: even a high performing window can underperform without correct installation and sealing.
Frequently Asked Questions
Is double glazing better than single glazing?
Yes for insulation, condensation and noise. Double glazing seals an insulating gap between two panes, which slows heat moving in or out of your home. It costs more upfront, and results depend on the glass, frame and installation, so it pays to specify the whole window.
Can I add double glazing to my existing single glazed windows?
Replacing only the glass can look cheaper, but existing frames often cannot properly support a double glazed unit. Full window replacement usually delivers better insulation, sealing and durability. That is why our installed prices include a complete uPVC frame made to fit your opening.
What does IGU mean in windows?
IGU stands for insulating glass unit. It is the sealed double glazed unit inside a window frame, made of two panes, a spacer and a gap filled with gas. In every Ultimate Windows unit the gap is filled with argon, which insulates better than plain air.
How much does double glazing cost compared with single glazing?
Double glazing costs more upfront than single glazing. Standard installed uPVC double glazed windows in Melbourne typically cost about $1,700 to $3,600 per opening. Fixed windows sit at the low end and double hung windows at the top. A free measure gives you a fixed price for your home.
Why is there moisture between my double glazed panes?
Moisture inside the sealed unit means the seal has been compromised and the double glazed unit needs to be replaced. It is inconvenient, but a glazier can usually sort it out quite easily. Moisture on the inside or outside surfaces has different causes and fixes.
Get a Free Measure and Double Glazing Quote
The right glass and frame depend on your home, so the most accurate answer comes from a free on-site measure. We manufacture your uPVC windows in our Wodonga factory and install with our own team, backed by a 12-year guarantee. Our quotes are itemised and fixed-price, with no hidden extras.
“We are thrilled with our new windows – they look great and make such a difference to temperature and noise.” Martha, Ultimate Windows customer. Request your free measure and double glazed window quote online or call 1300 898 782.
