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Revision of ISO 9972: Improvements in the reliability of airtightness measurements


ISO 9972 is an international standard describing the measurement procedure and calculation methods for determining the air permeability of buildings using the fan pressurisation method. Given the impact of airtightness on building energy use, more and more tests are performed, a lot of them required by regulations. Indeed, environmental conditions during the test, and more specifically wind and temperature differences, may cause significant errors and thus increase the result uncertainty. However, when a target value must be reached in a mandatory context, knowing the test uncertainty is crucial. Recent works have underlined the need to improve the reliability of the method to measure a building’s air leakage rate as described in ISO 9972.

To address these challenges, Cerema has launched a project to review ISO 9972 and has set up a working group of international experts in the field of building airtightness testing to identify the relevant issues with the current standard and propose improvements. This project aims to lay a foundation for a thorough review and revision of the current ISO 9972 standard and this session will present the first results towards this revision.


The objective of this session is first to give an overview of the project and summarise issues with the standard that are not correct or relevant, induce difficulties in performing the test, are inconsistent with other standards or are missing in the standards. In the second part, further research and studies conducted by members of the working group will be presented, including

  • presenting a series of in-situ fan pressurization tests that have taken place under various wind conditions. The objective is to investigate the uncertainty in airtightness tests due to wind conditions and discuss the important factors. Towards quantifying these uncertainties, an analysis of declared airtightness tests has been conducted. The findings indicate that the assessment of the impact of dynamic wind should consider the following factors: i) angular exposure of the blower door to the direction of the prevailing wind speed, ii) spectral energy distribution at low frequencies and gustiness of wind, and iii) the wind speed carrying the maximum energy.
  • investigating the integration of two new aspects in the fan pressurization measurement procedure: an uncertainty source related to the inhomogeneity of pressure difference along the building envelope and the autocorrelation of successive pressure difference measurements due to wind fluctuations. Those are integrated into the framework of uncertainty calculation and are then applied to a series of 30 tests conducted in repeatability conditions in an apartment in Brussels. Results show the relatively low impact of those additions to the determination of building characteristics and their large impact on both results variability and uncertainty assessment.
  • introducing and evaluating the reliability of conversion equations between different indicators for air tightness using different pressure references and various geometric parameters. To do so, a statistical analysis of the French database was conducted and the compactness factor was found to be a good representation of the building geometry. The results show that different indicators can be reliably estimated by knowing the building type and geometry.

Finally, a proposal for new implementations in the standard will be presented, and discussions with the audience will cover possible further improvements.


    1. Introduction to the project of ISO 9972 revision, Valérie Leprince, Cerema, France
    2. Impact of dynamic wind on leakage numbers obtained using fan pressurization method, Dimitrios Kraniotis, Oslo Metropolitan University, Norway 
    3. On the integration of envelope pressure inhomogeneity and autocorrelation in fan pressurization uncertainty analysis, Martin Prignon, Buildwise, Belgium
    4. Statistical analysis of the correlations between buildings air permeability indicators, Bassam Moujalled, Cerema, France
    5. Proposal for new implementations in ISO 9972, Benedikt Kölsch, Cerema, France
    6. Discussion with the audience


Valérie Leprince, Cerema, France

Gary Nelson, The Energy Conservatory, USA

   –90 minutes

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