It s often not wisdom at all and you may get different versions of it depending on which convention you believe.
Gap under bedroom door.
In the winter they let cooler air in and in the cooling season when your air conditioner is.
My contractor just hung our fancy dancy un painted solid wood door slabs in my 100 year old house with solid hardwood floors throughout.
Cheaper pre hung doors give about 1 1 25 clearance and this is because the rise of thinner floor systems for the mass consumer market.
Gap under interior doors let me get more specific if the conditions will likely end up with a door mat like a front entry door 3 4 is more appropriate.
But for finished conditions bedroom closets area with w to w carpeting ect 1 2 max.
How to fix a gap under a door.
Seal the gap under the door.
Higher quality pre hung doors are usually manufactured with 1 5 clearance under the door as described above assuming the flooring will be premium as well in the 3 4 range.
I think it is too big and think a 1 4 1 2 gap would accommodate any unevenness in our floors and allow us to use area rugs.
Door undercuts typically won t allow enough air to get out of the bedroom unless you leave a gap bigger than most people want under their doors.
The conventional wisdom on door undercuts.