Tempered vs Laminated Glass U-Value Calculator
Calculate and compare the thermal transmittance (U-value) for tempered and laminated glass configurations, including single, double, and triple glazing options.
Glass Configuration
Environmental Conditions
Quick Reference U-Values (W/m²K)
- Single glazing: ~5.8
- Double glazing (air): ~2.8
- Double glazing (argon + Low-E): ~1.1–1.4
- Triple glazing (argon + Low-E): ~0.6–0.8
Formulas Used
Overall U-Value (ISO 10292 / EN 673):
U = 1 / Rtotal + ΔUframe
Rtotal = Rsi + Σ Rglass + Σ Rgap + Rso
Glass pane resistance: Rglass = d / k where d = thickness (m), k = 1.0 W/mK
Laminated interlayer resistance: Ril = dil / kil (PVB: k = 0.23 W/mK; SGP: k = 0.35 W/mK)
Gas gap total conductance: hgap = hc + hr
Convective component: hc = Nu · λgas / dgap (Nu ≈ 1.0–1.15 for vertical glazing)
Radiative component: hr = 4σTm³ / (1/ε₁ + 1/ε₂ − 1) where σ = 5.67×10⁻⁸ W/m²K⁴, Tm = 283 K
Heat flux: q = U · ΔT (W/m²)
Assumptions & References
- Thermal conductivity of glass (tempered and laminated): k = 1.0 W/mK (ISO 10456)
- Tempered and laminated glass have identical thermal conductivity; U-value difference arises from interlayer in laminated glass
- PVB interlayer: k = 0.23 W/mK; SGP: k = 0.35 W/mK; EVA: k = 0.35 W/mK (manufacturer data)
- Interior surface resistance Rsi = 0.13 m²K/W (ISO 6946, still air, vertical surface)
- Exterior surface resistance Rso = 0.04 m²K/W (ISO 6946, wind-exposed)
- Gas thermal conductivity at ~10°C: Air = 0.0241, Argon = 0.0163, Krypton = 0.00926 W/mK (EN 673)
- Nusselt number simplified for vertical glazing gaps (EN 673 / ISO 10292)
- Radiative heat transfer calculated at mean gap temperature of 10°C (283 K)
- Uncoated glass emissivity ε = 0.89; Soft coat Low-E ε = 0.04; Hard coat Low-E ε = 0.15
- Frame correction factors per NFRC 100 and EN 10077-1
- Center-of-glass U-value only; edge effects and spacer thermal bridging not included
- References: ISO 10292:1994, EN 673:2011, EN 10077-1:2017, ASHRAE Fundamentals Chapter 15