How to Optimise Low-E Double Glazing to Reach NCC 7-Star
Audience: Architects • Specifiers • Homeowners
Reading time: ~9–12 minutes
Summary: With Australia's shift to minimum 7-Star energy ratings and Whole-of-Home requirements, glazing specifications have become critical to compliance. This guide shows how to specify soft-coat Low-E double glazing units—with the right coating stacks, gas fill and warm-edge spacers (Ködispace 4SG / Super Spacer)—so your designs pass modelling with fewer compromises on comfort, daylight and aesthetics.
NCC 7-Star and Whole-of-Home Energy Requirements
Understanding the New Standards
NCC 2022 lifts new homes to a minimum 7-Star NatHERS rating and introduces Whole-of-Home energy budgeting. This represents the minimum thermal performance for new Australian homes under the National Construction Code (NCC 2022), measured by the NatHERS star rating (out of 10). A 7-star home requires significantly less heating and cooling than a 6-star home, while 10-star homes aim for year-round comfort with minimal mechanical conditioning.
What's Actually Assessed
Thermal Shell Rating (Stars):
This measures the building fabric's performance. It includes orientation, insulation, glazing performance (U-value/SHGC), and airtightness assumptions. The modelling produces a star rating, with 7 stars now the minimum benchmark nationally (subject to state adoption dates).
Whole-of-Home (WoH) Score (out of 100):
Added in NCC 2022, this sets an annual energy-use budget for fixed services including:
- Heating and cooling systems
- Hot water
- Lighting
- Pool/spa pumps
- Some plug loads
- Solar PV and battery contributions
You must achieve both 7 stars and meet the WoH budget to comply where adopted.
Moving from 6 to 7 stars materially reduces energy demand and improves occupant comfort. NCC 2022 couples this improvement with WoH requirements, ensuring both the building shell and its fixed appliances meet modern efficiency standards.
Low-E Double Glazing: The Fast Track to 7-Star
If your goal is achieving 7-Star compliance with minimal redesign, focus on the elements that provide the greatest improvement per dollar invested. In real projects, Low-E double glazing typically offers the quickest, least-disruptive path to 7-Star ratings.
The Three Critical Glazing Factors
- Glazing Upgrade to Soft-Coat Low-E Double Glazing
Incorporating argon gas fill and warm-edge spacers (Ködispace 4SG or Super Spacer) typically provides the largest single improvement in star rating without requiring façade redesign. Warm-edge spacers raise edge-of-glass temperatures and significantly reduce condensation risk. - Orientation and Shading
Protect west and north-west facades with external shading while admitting winter sun on northern exposures. - Frame Selection and Air-Tightness
Choose thermally improved frames and specify effective perimeter seals with quality installation practices.
Low-E Glass Types: Hard-Coat vs Soft-Coat
Low-E (low-emissivity) coatings reduce long-wave heat transfer through glass. Using soft-coat Low-E technology inside a double glazing unit delivers the lowest U-values and precise SHGC (Solar Heat Gain Coefficient) control—your most dependable path to 7-Star compliance with generous glazing areas.
Two Types of Low-E Coatings
Hard-Coat (Pyrolytic):
- Durable surface that can be exposed to the elements
- Often used in single glazing applications
- Generally less selective than high-performance soft-coat options
Soft-Coat (Sputtered):
- Must be sealed inside a double glazing unit for protection
- Delivers superior U-values and SHGC control
- Available in single, double, and triple-silver coating stacks
- Provides excellent selectivity (high visible light with low heat gain)
Key Insight: For projects targeting 7-Star compliance with generous glazing areas, soft-coat Low-E double glazing should be your default specification.
Performance Metrics That Matter
Glass performance can seem overwhelming, but success in your energy model depends on optimising four key metrics:
- U-Value (W/m²·K): Measures steady-state heat transfer through the glass. Lower values indicate better insulation for both heating and cooling efficiency.
- SHGC (Solar Heat Gain Coefficient): Represents total solar heat admitted through the glass (scale of 0–1). Lower values block more solar heat (beneficial for west/north-west facades), while higher values can improve passive solar gains in cooler climates.
- VLT (Visible Light Transmittance %): Indicates the percentage of visible light passing through. This must be balanced with glare control and occupant comfort requirements.
- Selectivity (VLT/SHGC Ratio): A quick indicator of "useful light without excessive heat". High-selectivity soft-coat Low-E double glazing delivers the natural daylight occupants desire while controlling unwanted solar gain.
Glazing Performance Comparison
This table shows typical performance improvements as you upgrade from single glazing through to high-performance Low-E double glazing. Values shown are centre-of-glass (CoG) measurements—always confirm with manufacturer datasheets for your specific products.
Note: Actual performance varies with frame type, spacers, and installation quality
Warm-Edge Spacers
A warm-edge spacer is a low-conductivity strip that separates the two panes in a double glazing unit. Traditional aluminium spacers act as thermal bridges, conducting heat around the Low-E coating. Warm-edge spacers replace aluminium with materials that conduct significantly less heat.
Benefits of Warm-Edge Spacers
- Reduced Thermal Bridging: Lower overall U-value compared to aluminium spacers
- Condensation Prevention: Warmer edge temperatures reduce condensation risk
- Consistent Performance: Preserves your soft-coat Low-E benefits across the entire glazing unit
- Improved Durability: Quality systems enhance gas retention and seal longevity
Recommended Warm-Edge Systems
Ködispace 4SG (Reactive Thermoplastic):
Extruded adhesive spacer forming part of the seal system, offering excellent gas retention and long-term durability.
Super Spacer (Flexible Foam/Silicone):
Closed-cell structural foam with integrated desiccant, providing superior movement accommodation and thermal performance.
Stainless/Polymer Hybrids:
Thin stainless steel with polymer backing—still significantly "warmer" than aluminium, commonly used in commercial applications.
Low-E Double Glazing: Six Specification Levers for 7-Star Performance
Optimise these six elements based on your climate zone and facade orientation to achieve both energy compliance and occupant comfort.
1. Coating Stack Selection
Single-Silver Soft-Coat:
Cost-effective upgrade from clear glass. Suitable for budget-sensitive projects or smaller glazed areas.
Double-Silver Soft-Coat:
The optimal choice for warm and temperate zones. Provides excellent SHGC control while maintaining good visible light transmission.
Triple-Silver Soft-Coat:
Maximum selectivity for heavily exposed facades and high window-to-wall ratios where comfort and glare control are critical.
2. Coating Surface Placement
Surface #2 (Outer Pane, Cavity Side):
Achieves lower SHGC values—ideal for solar control in warm/temperate climates and west/north-west facades.
Surface #3 (Inner Pane, Cavity Side):
Increases beneficial solar gains in cool/alpine climates without compromising U-value. Recommended for north and east facades where winter sun is desirable.
Technical Note: U-value remains relatively constant regardless of coating position, but SHGC changes significantly. Use surface placement to fine-tune performance by orientation.
3. Cavity Width and Gas Fill
- Standard cavity width: 12–16mm (diminishing returns beyond this range)
- Argon gas fill provides lower conductivity than air without colour distortion
- 90% minimum argon concentration recommended for optimal performance
4. Spacer Type Selection
Always specify warm-edge spacers:
- Ködispace 4SG or Super Spacer recommended
- Avoid traditional aluminium spacers which compromise edge performance
5. Glass Make-up and Thickness
Common configurations:
- 6/12/6 (6mm outer / 12mm argon cavity / 6mm inner)
- 6/14/6 or 8/12/8 for enhanced performance
- Laminated options available for safety or acoustic requirements without sacrificing thermal targets
6. Frame, Seal and Installation Quality
- Specify thermally broken or thermally improved frames
- Ensure proper drainage and ventilation in glazing rebates
- Use appropriate setting blocks and spacers
- Implement quality control checks during installation
Climate-Smart Application Guide
Australia's diverse climate zones require tailored Low-E double glazing specifications. Here's how to optimise for each region:
Warm to Hot Climate Zones (Higher Cooling Loads)
- Start with double or triple-silver soft-coat on Surface #2
- Target lower SHGC (0.25–0.35) while maintaining adequate VLT
- Always specify argon fill and warm-edge spacers
- Supplement with external shading for low-angle afternoon sun
Temperate Zones (Balanced Heating and Cooling)
- Prioritise balanced SHGC/VLT ratios
- Use Surface #2 placement on west/north-west facades
- Consider Surface #3 for north-facing glass to capture winter gains
- Add laminated inner panes for acoustic comfort in urban areas
Cool and Alpine Zones (Higher Heating Loads)
- Utilise Surface #3 placement to maximise winter solar gains
- Maintain low U-values with argon and warm-edge spacers
- Keep VLT reasonably high to support natural daylighting
- Consider triple-silver coatings for large glass areas
Managing Condensation Risk
Condensation complaints often originate at glass perimeter zones. Strengthen these critical areas with proper detailing:
- Always specify warm-edge spacers (Ködispace 4SG or Super Spacer) to elevate interior edge temperatures
- Detail proper drainage with ventilated rebates and correct packer placement
- Control indoor humidity through appropriate ventilation in wet areas and bedrooms
- Coordinate frame design ensuring thermal breaks align with glazing performance
Colour and Visual Consistency
For prominent facades, appearance is as critical as thermal performance. Follow these steps to maintain neutrality and manage reflectance:
- Define Visual Requirements
- Determine desired neutrality (clear vs tinted appearance)
- Set exterior reflectance limits
- Consider interior colour rendering under typical lighting
- Review Physical Samples
- Compare samples in natural daylight
- View at multiple angles
- Assess both transmitted and reflected colour
- Select Appropriate Coating Family
- Higher-selectivity coatings often appear more neutral
- Triple-silver minimises colour cast at low SHGC values
- Maintain Consistency
- Keep glass thickness uniform across facades
- Document all selections including coating surface and spacer type
Specification Templates
Use these templates in your documentation to ensure correct Low-E double glazing specification:
Template A: Solar Control for Warm/Temperate Zones
- IGU Specification: 6-8mm clear outer pane with soft-coat Low-E (double/triple-silver) on Surface #2; 12-16mm argon-filled cavity (90% minimum concentration); warm-edge spacer (Ködispace 4SG or Super Spacer); 6mm clear or toughened inner pane (laminated if required).
- Performance Targets: U-value ≤1.3 W/m²·K, SHGC 0.25-0.35 (west/north-west), VLT >60%
Template B: Passive Solar for Cool/Alpine Zones
- IGU Specification: 6mm clear outer pane; soft-coat Low-E on Surface #3; 12-16mm argon-filled cavity; warm-edge spacer (Ködispace 4SG or Super Spacer); 6mm clear or laminated inner pane.
- Performance Targets: U-value ≤1.5 W/m²·K, SHGC 0.45-0.55, VLT >70%
Template C: Acoustic and Thermal Performance
- IGU Specification: As per Template A or B, with laminated inner pane incorporating acoustic interlayer to achieve required Rw rating; maintain argon fill and warm-edge spacers as standard.
- Performance Targets: As above plus Rw ≥35
Note: Centre-of-glass values vary by specific make-up and coating selection. Consult current manufacturer datasheets for precise U/SHGC/VLT values.
Cost-Benefit Considerations
Typical Investment Returns
Note: Costs and returns vary by project scale, location, and energy prices
Common Specification Mistakes to Avoid
- Specifying Low-E without warm-edge spacers - Aluminium spacers can negate 20-30% of your Low-E performance
- Wrong surface placement for climate - Surface #2 in heating-dominated climates reduces beneficial solar gains
- Overlooking frame performance - High-performance glass in poor frames wastes investment
- Inadequate installation detailing - Poor drainage and ventilation cause premature seal failure
- Mismatched glass across facades - Creates visual inconsistency and complicates replacement
How to proceed with optimisation
Ready to optimise your project's glazing for 7-Star compliance?
Get Expert Support:
- Email our technical team your plans for a free glazing optimisation review
- Request detailed IGU datasheets and warm-edge spacer drawings (Ködispace 4SG / Super Spacer)
- Order visual samples to confirm colour neutrality and appearance
- Access our online Low-E double glazing specification calculator
Contact our Technical Team: info@coolingbrothers.com.au
Frequently Asked Questions
Where should I use soft-coat instead of hard-coat Low-E?
Use soft-coat Low-E when the glass is within a double glazing unit and you need superior U-values with precise SHGC control. This is essential for large glazing ratios, west-facing facades, or when targeting higher NatHERS ratings. Hard-coat Low-E suits exposed monolithic applications or when durability and cost are primary concerns with modest selectivity requirements.
Does Low-E double glazing alone guarantee 7-Star compliance?
No. The 7-Star rating is a whole-of-house outcome. While Low-E double glazing is often the most impactful single upgrade, it works in conjunction with orientation, shading, frame selection, insulation, and air-tightness to achieve compliance.
Should I specify Surface #2 or #3 for my project?
Use Surface #2 for stronger solar control in warm/temperate zones and on west facades. Choose Surface #3 to capture beneficial winter solar gains in cool zones and on north-facing glass. Always confirm the optimal configuration through energy modelling.
Do argon and warm-edge spacers really make a difference?
Yes—argon gas reduces U-values by approximately 0.2-0.3 W/m²·K, while warm-edge spacers improve edge-of-glass temperatures by 2-4°C, significantly reducing condensation risk. Together, they ensure your Low-E investment delivers maximum performance. Cooling Brothers manufactures with both Ködispace 4SG and Super Spacer systems.
Can I maintain high daylight levels while reducing heat gain?
Absolutely. High-selectivity soft-coat Low-E double glazing (particularly double and triple-silver options) delivers VLT values of 60-70% with SHGC as low as 0.25-0.35. Combine with appropriate external shading for optimal results.
What's the typical lead time for custom Low-E double glazing?
Standard soft-coat Low-E configurations: 2-3 weeks. Custom specifications or large commercial orders: 4-6 weeks. Contact Cooling Brothers early in your project timeline to ensure availability.
This guide is provided by Cooling Brothers Glass Company as a technical resource. For project-specific advice, consult with our technical team and your NatHERS assessor.
