On NESEA’S BuildingEnergy course Passive House Design course discussion board…
Takeaways:

Typically, Passive Houses do not feature crawlspaces (a foundation that is five feet or less, and fully enclosed — or, not vented to outside) because:

If the thermal boundary is at the home’s foundation walls, there is the added cost of the foundation wall and slab insulation.
At a minimum TFA […]