ISO 12631:2017

Overview

ISO 12631:2017 - Thermal performance of curtain walling - Calculation of thermal transmittance specifies a harmonized method to calculate the overall thermal transmittance (U‑value) of curtain wall systems. It covers curtain walls made of glazed and/or opaque panels set in or connected to frames and addresses the treatment of thermal bridges at rebates and junctions between glazing, frames and panels. ISO 12631 is part of the EPB (Energy Performance of Buildings) set of standards and is intended for consistent assessment of curtain wall thermal performance.

Key topics and technical requirements

• Two validated calculation approaches:
  • Single assessment method (Clause 7) - whole-element calculation for a full curtain wall unit.
  • Component assessment method (Clause 8) - modular approach aggregating component results.
• Treatment of materials and assemblies:
  • Glazing: glass or plastic, single/multiple panes, low‑emissivity coatings, gas‑filled cavities.
  • Frames: any material, with or without thermal breaks.
  • Opaque panels: metal, glass, ceramics or other claddings.
• Inclusion of linear thermal transmittance (Ψ) and thermal bridge effects at rebates and connections between glazed, frame and panel areas.
• Required inputs and outputs: geometrical characteristics, thermal properties of components, calculation time intervals and presentation of results (reporting templates in Clause 9 and Annex A).
• Normative and informative annexes provide templates, regional references, methods for junctions and screw effects, and guidance on ventilated/unventilated air spaces.
• Exclusions (not covered by ISO 12631):
  • Solar radiation effects
  • Air leakage heat transfer
  • Condensation risk calculations
  • Shutters; extra corner/edge heat transfer; connections to main building structure or through fixing lugs
  • Curtain wall systems with integrated heating

Practical applications - who uses it and why

• Manufacturers of curtain walling - to quantify and compare U‑values for product development, optimization and technical datasheets.
• Façade engineers and consultants - to model curtain wall thermal performance for energy simulations and detailing of thermal bridges.
• Architects and specifiers - to assess façade options and support compliance with building energy regulations.
• Regulators and certification bodies - as a reference method within national/regional EPB frameworks (national choices may be specified in a national annex).
• Energy assessors and building modelers - to provide inputs for building energy use calculations and compliance documentation.

Related standards

• ISO 10077‑2, EN 12412‑2 - frame U‑value and linear transmittance procedures
• ISO 10291, ISO 10292, ISO 10293 - glazing thermal properties
• ISO/TR 52022‑2 - calculation examples and supporting guidance
• ISO 12567‑1 - laboratory testing alternative for glazing/fenestration

Using ISO 12631:2017 helps ensure consistent, reproducible thermal transmittance calculations for curtain wall systems and supports informed decisions on façade design, product development and regulatory compliance.