While it is generally accepted that ventilation-whether natural, mechanical or hybrid- is needed to provide acceptable indoor air quality and prevent building damage, there are debates about the actual performance of these systems and how deviations observed affect the overall building performance.

The current development in building energy efficiency towards nearly-zero energy buildings represents a number of new challenges to building design and construction. One of the major challenges is the increased need for cooling present in these highly insulated and airtight buildings, which is not only present in the summer period but also in the shoulder seasons and in offices even during occupied hours in winter. In most post-occupancy studies of high performance buildings in European countries elevated temperature levels is the most reported problem, especially in residences.

With the trend towards low-energy buildings, the importance and the interest for building air tightness is increasing. This implies an increasing number of tests, calling for increased attention to the quality of those tests including the way the test results are used to justify for programme or regulatory requirements. In turn, those tests put pressure on builders and craftsmen to reliably attain good airtightness levels. The project will review existing approaches and will analyse their pros and cons.

There is no doubt that, as part of this tendency to move to nearly zero energy buildings, in most climates buildings have to become more airtight. Should there be specific airtightness requirements? If so, what level is to be required? Should there be a minimum level of air leakage? This is the context for this project regarding the ‘philosophy about airtightness requirements’.

There are several national initiatives to collect air leakage data from field measurements buildings as a whole, building components, or ductwork systems. However, at this stage, there is no structured communication between these actions although they could mutually benefit from sharing their experience and encourage other similar initiatives in other countries having in mind the lessons learnt from the previous ones.