Overview
EN ISO 10077-2:2017/A1:2025 is Amendment 1 to ISO 10077-2:2017 - the internationally used method for calculating the thermal transmittance (U‑value) of window, door and shutter frames using numerical modelling. Prepared under ISO/TC 163 and adopted by CEN, this amendment (ISO 10077-2:2017/Amd1:2024) was approved by CEN on 8 November 2024 and published as EN ISO 10077-2:2017/A1:2025. The update refines figures, example cases and input keys to improve clarity and alignment with EPB (Energy Performance of Buildings) standards.
Key topics and technical updates
- Numerical method for frames: Continued focus on the 2D numerical calculation approach for thermal transmittance of frame cross-sections (frame U and linear thermal transmittance L).
- Updated figures and keys: Many figures in Annexes F, H and I are replaced or extended with explicit keys identifying boundaries, materials (aluminium, PVC, wood, polyamide, EPDM, insulation panels), surface emissivities and adiabatic/internal/external surface resistance designations.
- Boundary and surface resistance clarifications: Table H.1 (boundaries) is updated to show adiabatic, external and internal surface resistances and associated temperatures or references to Annex E.
- Example cases and results: Annex H example profiles (Figures H.1–H.11) are revised and Table H.3 gives calculated thermal conductance (L) and frame thermal transmittance (Uf) values for those examples - values are provided to three significant figures to avoid rounding errors.
- Emissivity and material notes: Default emissivity values are specified (commonly 0.9; exceptions noted such as 0.1 in a specific figure), and projected frame widths for sample sections are listed where relevant.
- EPB harmonization: The amendment makes explicit that no optional choices are left open in this document, ensuring congruence with other EPB-related standards.
Applications and who uses it
- Window/door manufacturers: For product design, thermal optimisation and documentation of frame U‑values required for energy labelling and compliance.
- Thermal engineers and facade consultants: To calculate frame heat losses reliably using standardized 2D numerical methods.
- Test laboratories and certification bodies: For reproducible calculation methods used in compliance testing and certification of window/door systems.
- Regulatory authorities and energy assessors: To support building energy performance assessments and regulatory compliance where frame thermal transmittance contributes to overall glazing/element U‑values.
Related standards
- ISO 10077 series (Part 1 covers glazing calculation; Part 2 focuses on frames)
- EPB-related CEN standards for building energy performance and product declarations
Keywords: thermal performance, windows doors shutters, thermal transmittance, U‑value, numerical method for frames, EN ISO 10077-2 amendment, frame thermal calculation, CEN, ISO, energy performance.
