📋 Standards & Regulations
Complete reference of building standards and calculation methods implemented in ThermX.
Overview
ThermX implements calculations and validation methods from European (EN/ISO) and North American (NFRC, ISO 15099) building standards. All thermal calculations comply with these standards' methodologies.
EN ISO 10211:2007/2017 — Thermal Bridges
Thermal bridges in building construction — Heat flows and surface temperatures — Calculation methods
This is the primary standard for 2D heat transfer analysis of building construction details. It defines:
- 2D Finite Element Method for steady-state heat conduction
- Thermal resistance definitions (Rsi, Rse surface resistances)
- U-value and ψ-value (psi-value) calculations
- fRsi minimum surface temperature factor for condensation risk
- Validation test cases (Annex A.1, A.2) with reference solutions
- Mesh quality requirements (min angle ≥15°)
- Boundary condition types and application methods
ThermX includes built-in ISO 10211 Annex A validation cases (Case A.1 simple rectangle, Case A.2 metal beam in concrete slab) accessible from the Validation panel. Solver accuracy is verified against reference temperature points.
EN ISO 10077-2:2017 — Window Frames
Thermal performance of windows, doors and shutters — Calculation of thermal transmittance — Numerical method for frames
Extends ISO 10211 specifically for window frame and door assembly analysis:
- 2D FEM analysis of frame cross-sections
- Frame U-value (Uf) calculation from 2D thermal bridge analysis
- Integration with glazing U-value to determine whole-window U-value (Uw)
- Boundary conditions for interior and exterior surface films
- Spacer bar thermal effects in glazing cavities
ThermX calculates frame U-value (Uf) from the FEM solution. Window frame examples (aluminum, PVC, timber) are included in the sample files.
ISO 15099:2003 — Window Thermal Performance
Thermal performance of windows, doors and shading devices — Detailed calculations
North American standard (ASHRAE basis) defining detailed thermal analysis methods:
- Center-of-glass (Cog) U-value calculation
- Frame U-value (Uf) via 2D FEM (cross-reference to ISO 10077-2)
- Edge-of-glass effects and spacer thermal properties
- Solar and condensation analysis
- WINDOW software methodology compatibility
ThermX reports U-factor in SI units (W/m²K) compatible with ISO 15099 methodology. Frame 2D analysis matches WINDOW software conventions.
EN ISO 10456:2019 — Material Properties
Building materials and products — Hygrothermal properties — Tabulated design values
Defines thermal conductivity reference values for building materials:
- 37+ materials with tabulated λ values (W/m·K) at mean temperature 10°C
- Design values for moisture-adjusted conductivity
- Density, specific heat, water vapor diffusion resistance
- Temperature correction factors (if needed)
- Material uncertainty and safety factors
ThermX material library includes EN ISO 10456 conductivity values for concrete, brick, insulations, metals, and glazing. Custom materials allow user-defined properties.
EN ISO 6946:2017 — U-Value Calculation (1D)
Building components and building elements — Thermal resistance and thermal transmittance — Calculation methods
Standard methodology for 1D U-value (R-value) calculation of layered construction:
- Surface thermal resistance (Rsi, Rse) tables — Table 7
- Unventilated air layer resistances — Table 8 (cavity air gaps)
- Annex C: Surface conductance coefficients (convective + radiative)
- Annex D: Air cavities, emissivity, radiative exchange
- Annex E: Tapered/sloped insulation layers
- Annex F: Corrections (fasteners, rainwater penetration)
ThermX uses EN ISO 6946 Annex D for gas cavity thermal conductivity (air, argon, krypton). Boundary conditions apply Rsi/Rse values from ISO 6946 Table 7.
EN ISO 13788:2012 — Condensation Risk (fRsi)
Hygrothermal performance of building components and building elements — Internal surface temperature to avoid critical humidity and interstitial condensation — Calculation methods
Defines surface condensation risk assessment:
- fRsi factor — minimum surface temperature factor (0–1)
- Risk threshold: fRsi ≥ 0.72 (typical climate, 21°C int, 0°C ext)
- Relationship to interior surface temperature and dew point
- Mould growth risk assessment
- Interior relative humidity assumptions (55%, 60%, 80%)
ThermX calculates fRsi from FEM results. Results panel shows pass/fail at fRsi ≥ 0.72 threshold and displays minimum interior surface temperature.
NFRC — North American Window Rating Council
National Fenestration Rating Council simulation methodology for window and door thermal performance
North American standard for window thermal rating:
- Interior design conditions: T = 21°C (70°F), h = 8.29 W/m²K
- Exterior design conditions: T = -18°C (0°F), h = 26.0 W/m²K
- Frame and spacer 2D FEM analysis
- Center-of-glass U-value and solar heat gain (SHGC)
- Rating compliance testing methodology
ThermX Boundary Conditions panel includes NFRC preset with 21°C interior and -18°C exterior film coefficients. Select "NFRC Interior" and "NFRC Exterior" for standard window analysis.
CEN — Central European Window Standard
Central European window performance standard (Scandinavian, Eastern European)
European standard for window thermal performance:
- Interior design conditions: T = 20°C, h = 7.69 W/m²K (Rsi = 0.13)
- Exterior design conditions: T = 0°C, h = 25.0 W/m²K (Rse = 0.04)
- Frame 2D FEM analysis
- U-value calculation per EN ISO 10077
- Compliance with EN ISO 10211 requirements
ThermX Boundary Conditions panel includes CEN preset with 20°C interior and 0°C exterior. Select "CEN Interior" and "CEN Exterior" for European standard window analysis.
Standards Summary Table
| Standard | Scope | Key Calculation | ThermX Use |
|---|---|---|---|
| EN ISO 10211 | 2D thermal bridges | FEM, ψ-value, fRsi | Core solver validation, thermal bridge analysis |
| EN ISO 10077-2 | Window frames | Frame U-value (Uf) | Window frame 2D analysis |
| ISO 15099 | Window thermal performance | U-value, SHGC, edge/center effects | Detailed window analysis, NFRC compatibility |
| EN ISO 10456 | Material conductivity values | λ = design conductivity | 37+ material library |
| EN ISO 6946 | 1D U-value, cavities | R-total, air gaps, Annex D gas | Surface resistances, cavity conductivity |
| EN ISO 13788 | Condensation risk | fRsi ≥ 0.72 | Mould risk assessment in results |
| NFRC | North American window rating | U, SHGC at fixed T, h | NFRC boundary condition preset |
| CEN | European window standard | U-value per EN ISO 10077 | CEN boundary condition preset |
References
- EN ISO 10211:2007 — Thermal bridges in building construction — Heat flows and surface temperatures — Calculation methods
- EN ISO 10077-2:2017 — Thermal performance of windows, doors and shutters — Calculation of thermal transmittance — Numerical method for frames
- ISO 15099:2003 — Thermal performance of windows, doors and shading devices — Detailed calculations
- EN ISO 10456:2019 — Building materials and products — Hygrothermal properties — Tabulated design values
- EN ISO 6946:2017 — Building components and building elements — Thermal resistance and thermal transmittance — Calculation methods
- EN ISO 13788:2012 — Hygrothermal performance of building components and building elements
- NFRC 100-2010 — Procedure for Determining Fenestration Product U-Factors