The Canadian glazing industry operates across two measurement systems, multiple international standards, and a domestic regulatory framework that uses its own terminology. Fabricators and architects navigating net-zero tenders, heritage board submissions, and Step Code compliance packages need to understand not just what these terms mean, but how they interact — and where the numbers come from. This is the reference every specifier needs.
U-Value: the core thermal performance metric
U-value (thermal transmittance) measures the rate of heat transfer through a material per unit area per degree of temperature difference. In glazing, it is expressed in W/m²K (watts per square metre per kelvin). A lower U-value means less heat transfer — better insulating performance.
Two standards are used to calculate glazing U-values, and they produce different results from the same product. Understanding which standard was used is essential for interpreting any U-value claim.
EN 673:2011 — the European standard
EN 673 calculates the thermal transmittance of the centre pane of glass (centre-of-glass, or CoG U-value) using a standardised boundary condition: 0°C outdoor, 20°C indoor, no wind, radiation from a standard sky. This is the standard used by most European and Asian manufacturers, including Leadus Technology. The TÜV Rheinland report confirming U=0.40 W/m²K for VIG Horizon's 4TL+V+4T configuration was conducted under EN 673:2011.
NFRC 100-2010 — the North American standard
NFRC 100 calculates the thermal transmittance of the complete window assembly — glazing, frame, and spacer — under standardised boundary conditions (0°F/-18°C outdoor, 70°F/21°C indoor). NFRC U-values are whole-window U-values and are always higher than centre-of-glass U-values because the frame and spacer introduce additional thermal losses. US ENERGY STAR and NRCan Energy Rating calculations use NFRC methodology.
Critical for Canadian projects: When a VIG supplier quotes U=0.40 W/m²K, verify which standard was used. EN 673 U-values are centre-of-glass; they will be lower than the whole-window NFRC U-value for the same product. For Step Code compliance documentation, ask specifically whether the U-value is CoG (EN 673) or whole-window (NFRC 100).
R-Value: the reciprocal metric
R-value (thermal resistance) is the reciprocal of U-value: R = 1/U. It measures resistance to heat flow rather than heat flow itself. Higher R-value = better insulation. In Canada, R-values are often expressed in imperial units (ft²·°F·hr/BTU) in the construction industry, particularly for wall and roof assemblies, while glazing more commonly uses U-value (SI units).
| Glazing | U-Value (CoG) | R-Value (imperial) | R-Value (SI) |
|---|---|---|---|
| Single pane | 5.8 W/m²K | R-1 | 0.17 m²K/W |
| Double IGU argon | 1.2 W/m²K | R-5 | 0.83 m²K/W |
| Triple IGU argon | 0.65 W/m²K | R-8.8 | 1.54 m²K/W |
| VIG 4TL+V+4T | 0.40 W/m²K | R-14.2 | 2.50 m²K/W |
Energy Rating (ER): NRCan's composite metric
The Energy Rating (ER) is a composite performance index developed by Natural Resources Canada (NRCan) for the ENERGY STAR Canada program. ER accounts for U-value (heat loss through the glazing), solar heat gain coefficient (solar energy admitted), and air leakage, combined into a single number that represents net annual energy performance in a standardised Canadian climate.
A higher ER number is better. ER values range from negative (net energy loser) to positive (net energy contributor). ENERGY STAR Canada requires minimum ER values by climate zone: Zone 1 (Vancouver) requires ER 21, Zone 2 (Calgary) requires ER 29, Zone 3 (Ottawa, Montreal) requires ER 34.
Solar Heat Gain Coefficient (SHGC)
SHGC measures the fraction of solar radiation admitted through a glazing unit as heat gain. Values range from 0 (no solar gain) to 1 (complete transmission). In Canada's predominantly heating-dominated climate, moderate to high SHGC values (0.40–0.60) are generally desirable for south-facing glazing, as admitted solar energy reduces heating loads. For cooling-dominated exposures or glazing that faces north, lower SHGC values may be preferred.
The 2025 NECB update introduces more explicit SHGC requirements by climate zone and orientation — a departure from the previous approach of prescribing maximum U-values only. This makes whole-assembly SHGC a more important specification parameter for commercial projects complying with the 2025 code.
Visible Light Transmittance (VLT)
VLT measures the percentage of visible light that passes through the glazing assembly. For most commercial applications, higher VLT is desirable to maximise daylighting. High-performance Low-E coatings can reduce VLT compared to clear glass. Double silver Low-E coatings (such as D80 used in VIG Horizon's 4TL+V+4T) typically achieve VLT values of 68–72% — comparable to conventional clear double IGU despite their superior thermal performance.
"The number that matters depends on the project. U-value for Step Code compliance. ER for ENERGY STAR labelling. SHGC for passive solar design. Whole-window U for PHPP input. Knowing which standard produced which number is as important as knowing the number itself."
VIG Horizon Inc.