Insulation Door bottom seals
What gap is needed between door, floor and frame : Insulation Door Bottom Seals
Quote from Article entitled What gap is needed between door, floor and frame:
Between a leaf of interior doors and the floor it is required to leave a gap of at least 2 - 2.5 cm to provide natural ventilation. A gap of 4 cm is allowed for convenient and safe door opening.
The full version of the article can be found here.