ISO 6946-2017 (2021) PDF

Full title and description

Building components and building elements — Thermal resistance and thermal transmittance — Calculation methods. This international standard specifies both detailed and simplified calculation procedures for determining steady-state thermal resistance (R‑value) and thermal transmittance (U‑value) of building components and elements (excluding most glazed units, curtain walling, ground-contact components and intentionally ventilated assemblies).

Abstract

ISO 6946:2017 provides the methods to calculate thermal resistance and thermal transmittance of planar building components made of thermally homogeneous and certain inhomogeneous layers. The standard gives a detailed calculation route (for use with more advanced heat-transfer analysis, referencing ISO 10211) and a simplified arithmetic method for mixed-layer assemblies, and includes correction procedures (Annex F) for common deviations such as air voids, mechanical fasteners and inverted roof drainage effects. A corrected version of the published text was issued in December 2021.

General information

• Status: Published (International Standard, confirmed).
• Publication date: June 2017 (corrected version December 2021).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: Construction and building standards (ICS 91 — elements of buildings / thermal insulation and protection; commonly associated subcodes include 91.060 and 91.120).
• Edition / version: 3rd edition — ISO 6946:2017 (with corrected version released 2021-12).
• Number of pages: 40 pages.

Scope

Applies to calculation of steady-state thermal resistance and thermal transmittance of building components and elements consisting of thermally homogeneous layers and to a simplified method for certain inhomogeneous layers. Excludes doors, windows and other glazed units, curtain walling, components involving heat transfer to the ground, and elements designed to allow air permeation. The standard is intended for use when determining R and U values between two defined environments (e.g., internal and external or internal and unheated space).

Key topics and requirements

• Two calculation routes: detailed method (for rigorous heat‑flow analysis, linked to ISO 10211) and a simplified arithmetic method for mixed layers.
• Definition and use of design thermal conductivity (λ) or design thermal resistance (R) for material layers, with calculation rules for layer resistance and total resistance.
• Surface thermal resistances and default values; special procedures for low‑emissivity surfaces, wind effects and non‑planar geometries.
• Approximate correction procedures (Annex F) for: air voids in insulation, mechanical fasteners and effects specific to inverted roofs; corrections can be omitted if total correction is less than 3% of U.
• Rounding and reporting rules (presentation of final R and U results and required input data disclosure).
• Limitations: simplified method not suitable where insulation is bridged by metal (except where fasteners are treated via the correction procedure) and not intended for condensation-risk surface temperature computations.

Typical use and users

Used by architects, building physicists, energy assessors, façade and product manufacturers, thermal performance consultants, code authors and regulators for: calculating U‑values for compliance and energy modelling, specifying material R‑values, assessing construction details for thermal bridging, and producing labelled thermal performance data for products and assemblies.

Related standards

Commonly used alongside ISO 10211 (thermal bridges — detailed heat transfer analysis), ISO 10456 (building materials — tabulated thermal conductivity and other thermal values), ISO 52000‑1 (energy performance of buildings — EPB standards framework) and other regional/adopted standards for thermal performance; EN/ISO harmonized adoptions (where applicable) often reference ISO 6946 procedures.

Keywords

thermal resistance, R‑value, thermal transmittance, U‑value, building components, simplified calculation, detailed calculation, thermal bridge correction, surface resistance, ISO 6946, Annex F.

FAQ

Q: What is this standard?

A: An ISO international standard that defines methods to calculate steady‑state thermal resistance (R) and thermal transmittance (U) of building components and elements.

Q: What does it cover?

A: Detailed and simplified calculation procedures for homogeneous and certain inhomogeneous layered components, default surface resistances and correction procedures for air voids, fasteners and inverted roof effects; it excludes most glazed units, curtain walling and ground-contact heat transfer cases.

Q: Who typically uses it?

A: Professionals involved in building thermal design and compliance — architects, energy assessors, building physicists, product manufacturers and regulators.

Q: Is it current or superseded?

A: The third edition, ISO 6946:2017, is the current published edition and a corrected version was issued in December 2021; the standard is maintained and reviewed on ISO’s regular review cycle. Users should check national adoption status or more recent ISO activity if a later revision has been published after December 2021.

Q: Is it part of a series?

A: It forms part of the family of thermal and energy performance standards for buildings (EPB standards) and is commonly used together with ISO 10211 (thermal bridges), ISO 10456 (material thermal data) and ISO 52000‑1 (EPB framework).

Q: What are the key keywords?

A: Thermal resistance, thermal transmittance, U‑value, R‑value, building components, calculation methods, thermal bridge correction, surface resistance.