ISO 6946:2017

Overview

ISO 6946:2017 - "Building components and building elements - Thermal resistance and thermal transmittance - Calculation methods" specifies internationally harmonized calculation procedures for the thermal performance of opaque building components. The standard defines how to compute thermal resistance (R‑values) and thermal transmittance (U‑values) from the design thermal conductivities or thermal resistances of materials and products. It applies principally to components made of thermally homogeneous layers (including air layers) and provides both a detailed and a simplified calculation method.

Key Topics

• Scope and exclusions: covers walls, roofs and other opaque elements but excludes doors, windows and glazed units, curtain walling, components transferring heat to the ground, and elements designed for air permeation.
• Calculation methods: detailed and simplified procedures for determining thermal resistance and thermal transmittance using design thermal conductivities or resistances.
• Layer types: methods apply to thermally homogeneous layers; an approximate method for inhomogeneous layers (including effects of metal fasteners) is provided via a correction term in Annex F.
• Surface and air layer treatment: normative guidance for surface resistances (Annex C) and thermal resistance of airspaces (Annex D), including unventilated, slightly ventilated and well‑ventilated air layers.
• Special cases: treatment of tapered layers (Annex E) and templates for input/method selection (Annex A - normative; Annex B - informative defaults).
• Outputs and format: produces standardized output suitable for energy performance assessment and further use in building energy models.

Applications

ISO 6946:2017 is widely used for:

• Comparing alternative construction assemblies by U‑value/R‑value performance.
• Generating input data for whole‑building energy simulations and annual heating/cooling load calculations.
• Supporting compliance with building energy regulations and demonstrating thermal performance for permitting.
• Preparing technical specifications, product performance declarations, and manufacturer datasheets.
• Informing retrofit design, insulation selection, and detailing to minimise thermal bridges (note: major metallic bridging beyond Annex F is out of scope).

Who should use it

• Architects and building designers for validated envelope performance calculations.
• Thermal engineers and energy assessors preparing energy models and compliance reports.
• Regulators and code officials using standardized methods for legal requirements.
• Manufacturers and product certifiers preparing performance data for building components.

Related standards

• ISO 52000‑1 (modular EPB framework) - places ISO 6946 within the set of energy performance of buildings (EPB) standards.
• ISO/TR 52019‑2 - technical report accompanying EPB methodologies referenced by ISO 6946.

Keywords: ISO 6946:2017, thermal resistance, thermal transmittance, U‑value, R‑value, calculation methods, building components, air layers, metal fasteners, EPB standards.