In an article that’s sure to raise the hackles of the Passive House crowd, Joseph Lstiburek, a principal of Building Science Corporation, says the Passivhaus airtightness requirement — 0.6 ach @ 50 Pa — “doesn’t seem to be based on anything that makes any sense.”  He suggests the following: “if you get below 3 ach @ 50 Pa the comfort problems go away, things become predictable, and you save energy. Add the controlled ventilation piece and the combustion safety piece and nobody dies and nobody gets sick and life is good.”  In other words, remove large holes in the building envelope, install a controlled ventilation system, and use sealed combustion or power vented appliances. 

[+] Read BSI-053: Just Right and Airtight by Joseph Lstiburek.

Credit: The Energy Conservatory.