ISO 16957:2016 PDF

Overview

ISO 16957:2016 - Measurement of apparent thermal conductivity of wet porous building materials by a periodic method - specifies a non‑steady‑state (periodic) test method to determine the apparent thermal conductivity (and diffusivity) of wet porous building materials. The standard targets the effective thermal behaviour that includes latent heat transfer from vapour movement and provides procedures to evaluate measurement uncertainty related to moisture movement and non‑uniform moisture distributions. It is intended as a practical alternative to steady‑state methods (see ISO 10051).

Key topics and requirements

• Test principle: a periodic temperature input (sinusoidal or stepwise) is applied to a specimen; temperature responses at (at least) two points are measured to derive thermal diffusivity from amplitude ratios or phase differences.
• Apparent thermal conductivity: measures the effective conductivity including latent heat effects from vapour movement (denoted λ*).
• Scope limits:
  • Applicable to porous materials with bulk density ≳ 100 kg/m3 where radiative transfer is negligible.
  • Excludes cases with significant convection or gravity‑driven moisture/air movement and excludes very high moisture content where gravity effects cannot be neglected.
• Specimen handling: precondition to a uniform initial moisture content and make external surfaces impermeable during the test to minimize moisture redistribution.
• Apparatus: measurement in a climate chamber at mean sample temperature, heater + damping layers, refrigerant bath to control baseline temperature, thermocouples for temperature recording.
• Uncertainty evaluation: provides an approximation formula to estimate uncertainty from moisture movement and non‑uniform water content and guidance to set measuring conditions that meet an upper limit of uncertainty.
• Additional output: an estimate of heat transfer caused by vapour movement is included.

Applications and who uses it

• Material test laboratories performing hygrothermal property characterization.
• Building physics researchers and developers of hygrothermal models requiring accurate conductivity data for wet materials.
• Manufacturers of insulation, masonry, concrete, and other porous building products for R&D and quality control.
• Building energy modelers and facade engineers assessing performance loss due to moisture uptake and designing moisture‑resilient systems.

Related standards

• ISO 10051 - steady‑state method for thermal conductivity of moist building materials (contrast with ISO 16957’s periodic method).
• ISO 9346 - related terms/definitions used in hygrothermal testing.

Keywords: ISO 16957:2016, apparent thermal conductivity, wet porous building materials, periodic method, non‑steady‑state, thermal diffusivity, measurement uncertainty, hygrothermal properties.