Determination of air permeability of buildings according to IS0 9972 orEN 13829 - Proposal for clarifications

Building airtightness is an important parameter that canbe measured according to the International Standard IS09972 "Therm~~l performance of buildings -Determination of air permeability of buildings - Fanpressurization method".Since 2006, there is a second edition of the standardthat cancels and replaces the first edition (IS0 9972:1996).A modified version of IS0 9972: 1996 has been publishedby the European Committee for Standardization (CEN) asEuropean standard (EN 13829:2000).The standard provides good guidance for themeasurement of building airtightness but some aspectsshould be clarified for the need of national regulationsand in order to improve the comparability of the results.These aspects are mainly related to the measurementmethods and to the calculation of the air change rate atreference pressure difference.Depending on the chosen method, intentional openingin the building envelope are open, closed or sealed duringthe measurement. Based on the general guidance of thestandard, this paper gives a practical table with commonintentional openings and their status for each of the 3methods.The air change rate, n50 at 50 Pa pressure difference,is calculated by dividing the mean air leakage rate at 50Pa by the internal volume. Whle a precise guidance isgiven for the measurement of the mean air leakage rate,the standard refers to national reglations for thecalculation of the internal volume. It means that thewidely used n5" value is not directly comparable fromcountry to country. Therefore the authors propose apractical common method for the calculation of the netfloor area and the internal volume.Another consequence of the existence of differentineasurenlent methods is that the models that have beendeveloped for the estimation of annual infiltration rates inbuildings from the airtightness should be used with care.