Final Airtightness Test completed!
October 19, 2016
Today we had our final airtightness test and the result was... drum roll... 0.18ach @50Pa - again! Phew!
As described in this post about our intermediate test it is very common for a passivhaus building to have this test repeated during the course of the build so that any remedial works that may be required can be done at the appropriate time i.e. before the works are completely covered and the ‘problem’ areas are covered over.
The final test should be undertaken when the building is ‘complete’ in the sense that all components relevant to the test are finished i.e. wall linings, doors and windows fully installed, all services installed, all penetrations through the airtight and insulated envelope completed, and so on. It is worth noting that the MVHR exhaust and intake should either not be connected to the unit yet (as that constitutes a large hole to the outside) or all valve heads should be sealed temporarily.
This final test is also used for Building Warrant completion and so the tester will provide a report that states both the air changes rate and the permeability. These two values have different units and so measure the ‘leakiness’ of the building against different parameters.
The test is repeated a number of times to gain an average reading, and the building is tested when it is both pressurised and de-pressurised as this allows the test to reflect the performance of the building fabric in both conditions, and tests window seals under both of these conditions.
More information regarding airtightness testing and the differences between air changes (required for passivhaus) and permeability (required for Building Standards compliance) can be found in several publications on the Passivhaus Trust website.