Is building and ductwork airtightness testing mandatory?

It depends on the country and context of the measurement. Most EU countries include in their regulations either required or recommended minimum airtightness levels with or without mandatory testing. There are several countries (e.g., United Kingdom, France, Portugal, Denmark, Ireland) where, by regulation, airtightness testing is mandatory for certain building types or in the case of specific programmes [1].

[1] R. Carrié, M. Kapsalaki and P. Wouters, “Right and Tight: What´s new in Ductwork and Building Airtightness?,” BUILD UP energy solutions for better buildings, 19 March 2013.