Building a Passivhaus?

Building a masonry Passivhaus? How many airtightness tests would you do?

I had a meeting yesterday regarding air tightness testing a Passivhaus dwelling that is about to start construction in the north of Cumbria and the subject of the number of airtightness tests came up.

The client was under the impression that Green Building Store recommends 2 airtightness tests on masonry construction. In my experience with low air permeability buildings, this is quite a big risk to take if you and your builder have not built a Passivhaus before.

For masonry construction with wet plaster, it is the plaster which is often providing the airtightness layer, so the initial test is primarily used for determining areas of missing / defective taping and will not provide an accurate airtightness figure for the property as there will be air movement through the blockwork. If a further test is not then done after first fix, the likely airtightness figure will be an unknown until the final test. This will increase your stress levels significantly!

If you’re an experienced Passivhaus builder with an experienced Passivhaus team and a set methodology,  I can see only 2 tests could potentially be OK. But if you do a risk analysis of the consequences for the first time Passivhaus builder , the more prudent strategy would be to weigh up the potential risks of not achieving your desired airtightness standard and cost of remedial work vs the cost of an additional airtightness test after first fix.

Three tests has been the norm on other relatively airtight masonry buildings I have tested.