Low-E glass (low emissivity glass) is double glazed glass with a microscopically thin metallic oxide coating that reflects heat while letting natural light through. In Melbourne homes, it reduces heat loss in winter by up to 70% and blocks solar heat gain in summer — cutting heating and cooling energy use significantly without tinting your windows.
What Is Low-E Glass?
Low-E glass — short for low emissivity glass — is glass that has been coated with a transparent metallic oxide layer so thin it's invisible to the naked eye. This coating dramatically changes how the glass manages heat energy, without changing how much natural light comes through.
The term "emissivity" refers to a material's ability to emit (radiate) thermal energy. Standard glass has high emissivity — it readily absorbs and re-radiates heat in whichever direction is hottest. Low-E glass has low emissivity — it reflects that radiant heat back rather than absorbing and passing it through.
In a Melbourne winter, that means your indoor heating stays inside. In summer, it means the sun's radiant heat bounces off before it can warm your living room.
How Does Low-E Glass Work?
Think of it like a thermal mirror built into your window. It's transparent to light but reflective to heat — working in your favour regardless of the season.
Hard Coat vs Soft Coat Low-E Glass
There are two types of Low-E coatings, each applied differently and suited to different applications. Understanding the difference matters when you're specifying windows for a Melbourne home.
- Applied during glass manufacturing (fused to surface)
- More durable — can be used in single glazed units
- Higher U-value (less thermally efficient)
- Slight blue/green tint visible in some conditions
- Lower cost; suitable for milder climates or budget builds
- Good for coastal areas with salt air exposure
- Applied after glass manufacture via vacuum deposition
- Must be sealed inside a double or triple glazed unit (IGU)
- Lower U-value = superior thermal performance
- Better solar control — ideal for Melbourne's varied climate
- Near-clear appearance — virtually invisible coating
- Standard in Windows Republic uPVC double glazed units
Low-E Glass Performance: U-Value Comparison
The U-value measures how much heat transfers through a window per square metre per degree of temperature difference. Lower is better — it means less heat escaping in winter and less heat entering in summer.
| Glass Type | U-Value (W/m²K) | Solar Heat Gain (SHGC) | UV Blocked |
|---|---|---|---|
| Single glazed (standard) | 5.8 | 0.87 | ~25% |
| Double glazed, no Low-E (air fill) | ~2.7 | 0.70 | ~40% |
| Double glazed + Hard Coat Low-E | ~2.2 | 0.60 | ~65% |
| Double glazed + Soft Coat Low-E (air fill) | ~1.8 | 0.38 | ~95% |
| Double glazed + Soft Coat Low-E + Argon Windows Republic | 1.6 | 0.28–0.32 | ~99% |
*Whole-window U-values vary by frame type, size, and installation. Source: AGWA / WERS reference data.
Low-E Glass in Melbourne & Victoria: Climate Zone 6
Melbourne sits in NatHERS Climate Zone 6 — a temperate zone with cold winters and hot summers. This is the most demanding climate zone for window performance in Australia because windows need to do two jobs: keep heat in during winter and keep heat out during summer.
Low-E glass with argon gas fill is specifically recommended for Climate Zone 6 by the Australian Glass & Window Association (AGWA) and is required to achieve a 7-star NatHERS energy rating in new Melbourne builds.
🗺️ Australian Climate Zones & Low-E Recommendations
Low-E Glass & the NCC 2025 Building Code
Under the existing NCC 2022 (still in force until May 2026), new residential buildings must achieve a minimum 7-star NatHERS energy rating. Windows account for up to 40% of a home's heat loss — meaning your glass specification is one of the highest-impact decisions you make.
Low-E double glazed windows in uPVC frames can contribute up to 1–2 NatHERS stars of improvement compared to single-glazed aluminium windows, depending on the home's glazing area, orientation, and construction — a meaningful uplift from a single product upgrade.
→ NCC 2025 & your windows explained → Double glazed windows Melbourne
Low-E Glass in uPVC vs Aluminium Frames
Low-E glass improves performance in any window frame — but the frame material significantly affects the overall thermal result. Here's why the combination of soft coat Low-E glass with uPVC frames outperforms aluminium for Melbourne's climate.
- Aluminium conducts heat ~1,000× more than uPVC
- Cold bridging at frame edges creates condensation
- Low-E glass performance partially negated by frame heat loss
- Thermally broken aluminium reduces (but doesn't eliminate) this
- Typical whole-window U-value: 1.9–2.6 W/m²K
- uPVC is a natural thermal insulator — no cold bridging
- Multi-chamber frame design traps additional insulating air
- Low-E glass + uPVC frame work together, not against each other
- No condensation on frames in Melbourne winters
- Typical whole-window U-value: 1.4–1.6 W/m²K (WERS-rated)
The difference in real terms: a uPVC double glazed Low-E window can perform 3–4× better than a standard aluminium single-glazed window on U-value — and up to 20% better than a thermally broken aluminium Low-E window.
→ uPVC vs Aluminium frame comparison
How to Tell If Your Glass Is Low-E
Not sure whether your existing windows have a Low-E coating? There are several ways to check — no specialist equipment required.
- The lighter test: Hold a lit lighter or match near the glass. You'll see four reflected flames (two panes = four reflections in a double glazed unit). In a Low-E unit, one of the reflections will appear a slightly different colour (often green or blue-tinged). If all four look identical, it's likely standard glass.
- Check the spacer bar edge: Look at the edge of the double glazed unit from inside — the spacer bar often has a small stamp or sticker identifying the glass specification, including whether it's Low-E.
- Ask your installer or check documentation: Windows Republic provides a full glazing specification with every installation, including coating type, U-value, and argon gas fill confirmation.
- Temperature test: On a cold Melbourne morning, press the back of your hand against the inside glass surface. Standard single glazed glass will feel noticeably cold. Low-E double glazed glass in a uPVC frame should feel close to room temperature.
Is Low-E Glass Worth It for Melbourne Homes?
In short: yes, especially in Melbourne's Climate Zone 6. Here's why the numbers stack up.
| Factor | Standard Single Glazed | Double Glazed Low-E uPVC |
|---|---|---|
| Winter heat loss through windows | High — up to 40% of home's heat | Reduced by up to 70% |
| Summer heat gain | Significant — drives AC usage | Reduced by ~40% |
| Condensation in winter | Common — mould risk | Eliminated on glass and frame |
| UV damage to furnishings | Significant — fading within 2–3 years | ~99% UV blocked |
| NatHERS energy star contribution | Baseline | +1 to +2 stars (varies by home) |
| Estimated annual energy saving | — | Varies by home size and glazing area — get an NatHERS assessment for a site-specific figure |
Add in the reduction in UV furniture damage, elimination of condensation-related mould issues, and NCC compliance benefits — and uPVC Low-E double glazing has a product lifespan of 30+ years with ongoing energy, comfort, and resale benefits from day one.
How Much Does Low-E Glass Cost?
Low-E glass is not sold separately — it's specified as part of a double glazed unit (IGU). The cost of a window with Low-E double glazing depends on several factors:
| Cost Factor | Impact |
|---|---|
| Window size | Larger = more glass area = higher cost |
| Frame material (aluminium vs uPVC) | uPVC is comparable in cost; thermally broken aluminium is typically higher |
| Soft coat vs hard coat Low-E | Soft coat (the better performer) adds a small premium |
| Argon gas fill | Adds modest cost; significantly improves U-value |
| Number of windows | Volume discounts apply — whole-home projects are more cost-efficient per window |
| Australian Made vs imported WR advantage | Windows Republic manufactures in Cheltenham — no importer margin, better price control |
Windows Republic provides free itemised written quotes — so you know exactly what you're paying for before committing. There are no surprises at installation.
→ Double glazed windows cost Melbourne
Frequently Asked Questions: Low-E Glass
Get Low-E Double Glazing — Made in Melbourne
Windows Republic manufactures uPVC double glazed Low-E windows at our Cheltenham factory. Free measure, itemised quote, and no importer margin.
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