Lars Due
Bibliographic info:
11th International BUILDAIR Symposium, 24- 25 May 2019, Hannover, Germany

For approx. a year ago, the following was submitted to the Certification Committee, and no response is still seen. Especially the problem of the pressure at which Pa the measurement should start is seen as a criticism, and yet it has not been possible to find a reasonable explanation for the change.

Dear committee at ISO 9972,

I miss an explanation, of the change that came from EN 13829 to ISO 9972

DS 13829 says the pressure on the test is to be carried out in the range 25 to max. 90 Pa (the 90-100 Pa is a recommendation to not damage the buildings), but it says, that the test is recommended to run at the high end, as it will increase accuracy, which fits well with practical experiences. At point 5.3.4, the minimum pressure difference must be min. 10 Pa or 5 times the baseline pressure i.e. 25 Pa, for example, started at 35 Pa as the lowest pressure, the conditions were met. Change in ISO 9972 says that the starting pressure should be approx.

10 Pa or 5 times baseline. But the standard also says, like the old, that the higher the pressure the better measurement and it is directly contrary to starting at 10 Pa.


We have a little exposed position and a windy day about 6 m/s and with some dynamic wind pressor. We see that the baseline of max 5 Pa is ok, measure 4.99 Pa, i.e. ISO 9972 says we should start about 25 Pa. The interval should be approx. 5 Pa, i.e. I test at 25, 30, 35, 40, 45, 50, 55, 60 Pa. Eight measuring points meet the conditions fine. If you have wind gusts around the building, the outside pressure will vary between ± 5 Pa, i.e. that’s means, at 25 Pa the actual pressure difference is between 20 and 30 Pa during the measurement, the percentage variation is then becoming approximately 17 %. Instead, we choose to start at 45 Pa, then we get fluctuations between 40 and 50 Pa. But the percentage variation is only 10%, is said in another way, a high pressure can better absorb the gusts.

Looking at it mathematically and statistically, mathematicians say that by a regression line there should be as many measurement points at both sides of the reference, but in practice where a new house is built in a windy place, it means, that the measurements become much more accurate, at a higher measuring range. So the little change from DS13829 to ISO 9972 where a min. has changed to approx. initial value, means that all measurements will be slightly more inaccurate than necessary. And it's actually difficult to get an acceptable measurement through, when you start down at such low pressures (10 Pa).

I want to start a standard deviation on this point in Denmark, but the best thing was of course that we got changed the standard. I am aware that my colleagues in Germany have been working on the same problem, but I do not know if the German standardization committee has moved on, but my German colleagues fully agree with my consideration.

If the committee has some reasonable explanation for the changes, then I would like to hear it, and will evaluate my opinion on this point, if it makes sense.

On behalf of people and companies in Denmark who perform BlowerDoor test.


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