Most houses can be tested by a single door fan but larger non-domestic buildings often need multiple fans to flow sufficient air through them to generate sufficient test pressures.
There are different levels of test technicians for different sized buildings, most houses fall within the basic L1 qualification, however for larger buildings and multiple fan tests then a technician must be qualified to L2 standard. Passivhaus testing also requires an additional qualification that is only available from the ATTMA accreditation body and allows the qualified technician to test Passivhaus to a methodology known as TSL4.
Good air-tightness of a building is best achieved by attention to detail and diligence during the construction of the basic envelope where walls, floors and roofs are accessible and visible before being covered up by finishes, sanitaryware, services and kitchen units to name but a few things. Time spent on air-tightness at this stage can save many more hours trying to deal with problems once the build is complete. For this reason it is worthwhile considering the effectiveness of your materials and design throughout the entire build phase.
Another critical thing to consider is how well the differing envelope elements join together as a great deal of leakage occurs through the uncontrolled gaps at the junctions between floors, walls, roofs, windows, doors and service entry points.
If in doubt it is prudent to contact an air leakage tester early on in the build to ensure any potential leak areas are identified and sealed as construction progresses.
Different materials act and perform in varying ways with regard to air-tightness, for example concrete blockwork can leak quite badly if not properly finished and plastered over, metal cladding and polythene membranes are often better at retaining air if correctly designed and installed.
The air leakage test is generally carried out at completion of the building, at this time all designed ventilation is temporarily sealed so as to be excluded from the test result. Ventilation equipment isn’t included in the test as it is classified as designed or intended, which therefore can be controlled by the building user as required.
A good test technician will be able to locate and identify any areas of excessive air leakage from a building during the test, a test fan is used for the vast majority of tests and this equipment can also trace air leaks when coupled with a smoke generating device that can visually indicate the path air takes from the inside to outside of the building.