If you believe some of the things you hear about Passivhaus, you might think each one was a suffocating prison of stale, unhealthy air, sealed off from the outside world behind locked windows.  Mark Siddall, architect and Certified Passivhaus Designer, does a little myth busting and sets some facts straight, before exploring some areas where neither natural ventilation, mechanical ventilation, nor even the Passivhaus standard, have absolutely all the answers.