Interesting. What sort of total ACH are you seeing? I have not found these recommended values to be too far off myself? For the type of work we do (Passive House in the US) the limiting value for Certification is 0.06 cfm/ft2@50Pa (IP units… I know… ) which converts to 0.000059 m3/s-m2@4Pa:
so about 40% less that the ‘tight building’ in the suggested values there, which seems roughly about right to me? At least in the right ballpark. For contrast, the commercial energy code in NY State requires only 0.4 cfm/ft2@75Pa (pathetic) which equates to 0.0003 m3/s-m2@4Pa.