Cellar Door

Question:

Our cellar door does not lie completely flat. How do I work out whether it is upright enough to affix a mezuzah on its post?

Answer:

If the top of the post rises to a point that is ten tefachim above the ground, you should affix a mezuzahwithout a berachah. Of course, the doorway itself must be 10 tefachim long.^[1]

[1] Agur B’ohalecha 22:19, citing Chazon Ish, Eruvin 7:6,11.