Low emissivity glass is no longer a niche product; it’s rapidly becoming the baseline for energy-conscious architecture. But specifying it well is more complex than simply writing “Low-E glazing” in a window schedule. Different coatings, colours, positions in the IGU, U-values and SHGC ranges can make the same façade either a high-performing envelope or an expensive missed opportunity.
This guide walks you through how to specify low emissivity glass step-by-step, so your projects balance performance, comfort and aesthetics without nasty surprises during tender or value-engineering.
1. Start With the Design Intent and Climate
Before you open a glass catalogue, be clear on what the building needs the glass to do:
- Climate zone
- Cold / heating-dominated
- Hot / cooling-dominated
- Mixed or temperate
- Primary design drivers
- Energy reduction and code / green rating compliance
- Visual transparency and daylight
- Glare control for workspaces
- Acoustic performance
- Architectural expression (colour, reflectivity)
In cold climates you’ll often favour passive low emissivity glass that allows useful solar gain while reducing heat loss. In hot climates, you’ll prioritise solar-control low emissivity glass that aggressively limits solar heat gain while maintaining daylight.
For a deeper comfort focus, it’s worth also understanding why low emissivity glass improves indoor comfort in the first place—stabilising surface temperatures, reducing radiant asymmetry and cutting glare. You can explore this in more detail here:
👉 Why Does Low Emissivity Glass Improve Indoor Comfort?
2. Define Performance Targets (U-Value, SHGC, VLT)
Every low emissivity glass spec should be tied to measurable performance. The three big metrics are:
- U-value (W/m²·K) – How much heat flows through the glazing.
- Lower = better insulation.
- Typical targets:
- Standard double glazing: ~2.7 W/m²·K
- Good Low-E double glazing: 1.0–1.6 W/m²·K
- High-performance triple Low-E: 0.5–0.8 W/m²·K
- Solar Heat Gain Coefficient (SHGC) – Fraction of solar energy admitted.
- Lower = less solar heat gain; higher = more passive solar.
- Cold climate south façades may use SHGC 0.45–0.60.
- Hot climates or large west façades may target 0.20–0.35.
- Visible Light Transmittance (VLT or Tvis) – Percentage of daylight that passes through.
- Higher = brighter interiors but potentially more glare.
- Offices often look for 50–70% VLT; highly glazed warm façades might accept 40–55% with more solar control.
In your specification, avoid vague language like “high performance Low-E glass” by itself. Instead, define ranges:
“Low emissivity glass with centre-of-glass U-value ≤ 1.3 W/m²·K, SHGC 0.30–0.38, VLT ≥ 55%.”
This gives suppliers latitude while locking in the thermal, solar and daylight behaviour you need.
3. Choose the Right Low Emissivity Glass Type
Hard-coat vs Soft-coat Low-E
When specifying, clearly indicate whether you’re expecting a hard-coat (pyrolytic) or soft-coat (MSVD) solution:
- Hard-coat Low-E
- Applied during float glass production.
- Very durable, can be exposed, suitable for single glazing or laminated exterior panes.
- Typically higher emissivity and SHGC (less aggressive solar control).
- Good for cold climates, retrofit storms, or where robustness and cost control matter.
- Soft-coat Low-E
- Applied in vacuum chambers after the glass is formed.
- Needs to be sealed inside an IGU (2nd or 3rd surface).
- Offers much lower emissivity, better U-values and fine-tuned SHGC.
- Ideal for high-performance façades, triple glazing and projects targeting advanced energy codes.
If you’re balancing several layers of performance—thermal, colour, reflectivity—soft-coat families provide the largest palette. For a more technical breakdown of these coating families, you can refer to:
👉 What Low Emissivity Glass Colors and Reflective Options Exist?
4. Specify Glass Colours, Reflectivity and Aesthetic Intent
Modern low emissivity glass isn’t just “clear with a slight tint”; it comes in a spectrum of visible tones and reflectivity levels that dramatically influence the façade’s character.
Colour / Tone
Decide how you want the façade to look from outside and inside:
- Neutral clear – Minimal colour shift; good when material honesty and clean lines are important.
- Cool blue-green neutrals – Common in commercial towers; read as high-tech and contemporary.
- Warm grey / bronze – Softer expression; can complement masonry or timber cladding.
In your spec, call out whether the design intent is:
“Neutral low emissivity glass with minimal internal colour shift,”
or
“Cool low emissivity glass with slight blue tone for a contemporary reflective façade.”
Reflectivity
Low emissivity glass can be tuned from very low exterior reflectance (almost invisible) to highly mirror-like. Consider:
- Urban context: Do you want your building to visually recede, or create a reflective statement?
- Light pollution: High reflectivity can brighten surrounding streets or disturb neighbouring residences at night.
- Interior views: Higher reflectivity improves daytime privacy but may increase night-time mirror effect inside.
A good performance spec may include:
“Exterior visible reflectance 10–18%, interior reflectance ≤ 20%.”
This keeps mirror-like effects under control while still allowing a subtle, premium sheen. For deeper discussion on how colour and reflectance intersect with performance, see:
👉 Low Emissivity Glass and Its Daylight–Solar Control Balance
5. Get the Layer Build-Up and Coating Position Correct
Even the best low emissivity coating can underperform if it’s on the wrong surface within the IGU.
For a typical double or triple glazed unit, surfaces are numbered from outside to inside:
- Double glazing:
- 1 = exterior face of outer pane
- 2 = cavity face of outer pane
- 3 = cavity face of inner pane
- 4 = interior face of inner pane
- Triple glazing:
- 1/2/3 on outer lite, 4/5/6 on inner lites
Hot / cooling-dominated climates:
- Use solar-control low emissivity glass on surface #2 of double or triple units to reflect heat before it enters the cavity.
- Optional secondary low emissivity coating on surface #3 or #5 for even lower U-values.
Cold / heating-dominated climates:
- Place passive low emissivity glass on surface #3 or #4, reinforcing interior heat retention while still admitting useful solar gain.
Clearly state in your spec:
“Soft-coat solar-control low emissivity glass, coating on surface #2, argon-filled cavity, warm-edge spacer.”
This avoids mis-fabrication and protects your thermal model assumptions.
6. Consider Acoustic and Comfort Requirements
Low emissivity glass by itself mainly deals with radiant heat and solar control, but architects increasingly combine it with laminated and acoustic build-ups to improve overall indoor experience.
Key strategies:
- Combine low emissivity glass with laminated inner panes for better sound reduction and safety, especially in urban or high-traffic sites.
- Vary pane thicknesses (e.g., 6 mm outer, 8.76 mm laminated inner) to avoid coincident frequencies that reduce acoustic performance.
- Ensure your specification calls for tested Rw/STC values, not just “acoustic glass”.
If the project prioritises quiet interiors—schools, hotels, apartments near highways—coordinate the glazing and acoustic consultants early. For more on how low emissivity glazing can be paired with sound-control systems, see:
👉 How Low Emissivity Glass Improves Indoor Acoustics?
7. Coordinate Low Emissivity Glass With Frames, Shading and Facade Systems
Even perfect glazing can be compromised by weak surrounding components. When you specify, consider:
- Frame material and thermal breaks
- Aluminium with robust thermal breaks or insulated steel for commercial projects.
- High-performance timber or uPVC for residential.
- Spacer bars
- Warm-edge spacers reduce perimeter thermal bridging and condensation risk.
- Integrated shading
- External fins, brise-soleil, or vertical fins supporting low SHGC requirements.
- Interior blinds for glare and privacy; coordinate cavity widths if using between-glass blinds.
- Operability
- Opening ratios may impact effective acoustic and thermal performance.
Your documentation should link the glass performance with whole-system performance—e.g., requiring frame U-values that complement the centre-of-glass U-value.
8. Address Cost, Availability and Value-Engineering Risk
Low emissivity glass is a premium product, and quantity surveyors or contractors will often look to value-engineer it. Get ahead of this by:
- Specifying performance, not a single proprietary name, but including acceptable alternates that meet exact U-value / SHGC / VLT bands.
- Clarifying minimum quality levels:
- Maximum allowable colour variance between panes.
- Distortion limits for large units or curved glass.
- Tempering / heat-soak requirements to reduce spontaneous breakage.
- Understanding regional supply:
- Which low emissivity glass families are locally stocked?
- Lead times and fabrication constraints for jumbo sizes or complex shapes.
If cost becomes a key design conversation, it’s useful to relate performance back to lifecycle value. For more context on what drives installed pricing, you can read:
👉 What Affects Low Emissivity Glass Pricing Across Projects Today?
9. Document Low Emissivity Glass Clearly in Your Specifications
To avoid ambiguity, your final architectural spec and schedules should include:
- Glass make-up
- Example: 6 mm toughened soft-coat solar-control low emissivity glass / 16 mm argon-filled cavity / 10.76 mm laminated clear inner pane with PVB interlayer.
- Performance values (centre-of-glass)
- U-value (W/m²·K)
- SHGC
- VLT
- External and internal reflectance
- Coating position
- e.g., “Low-E coating on surface #2; laminated inner pane on surface #4.”
- Additional requirements
- Warm-edge spacers, gas fill type and minimum percentage.
- Safety classification (e.g., toughened / laminated to relevant standard).
- Acoustic rating where applicable.
- Colour and reflectivity tolerances.
- Mock-up and testing
- Require a full-size visual mock-up for key façade orientations.
- For performance-critical projects, consider in-situ U-value or infrared checks after installation.
10. Integrate Low Emissivity Glass Into Holistic, Future-Ready Design
Finally, remember that low emissivity glass is one piece of a much bigger puzzle. High-performance envelopes are increasingly expected to work alongside:
- Smart shading and BMS-controlled blinds
- Photovoltaic façades and smart windows
- Biophilic and landscape-integrated design, especially in dense urban and smart-city contexts
If you’re working at the urban scale, façade performance should sit alongside streetscape, planting, water management and public-realm design—topics explored in resources such as:
👉 Define Landscape Solutions in Smart Cities
By thinking of low emissivity glass as a strategic component rather than just a line item, you’ll create buildings that are more comfortable, efficient and future-proof.
Key Takeaways for Specifying Low Emissivity Glass
- Start with climate and design intent, not products.
- Lock in performance ranges for U-value, SHGC and VLT.
- Specify hard-coat vs soft-coat and coating position explicitly.
- Coordinate colour and reflectance with the architectural concept.
- Combine low emissivity glass with acoustic, safety and shading strategies as required.
- Write specifications that are clear, testable and resilient against value-engineering.
Do that, and your low emissivity glass choices will genuinely elevate building performance—cutting energy use, improving comfort and supporting the next generation of sustainable architecture.