In a session today we were camped out in a Leomund's tiny hut and the DM determined that since it is described as a dome, the bad guys (Wraiths, so they are incorporeal) could enter the area from below. I went with it and it was a fun encounter, but I wondered what other people think about it. I can see two arguments.
His argument: It is described as a dome. So only the semi-spherical outside prevents things from happening. A dome doesn't (necessarily) have a floor, they can enter no problem.
My argument: The intent of the spell seems to be to prevent baddies from coming in. The rest of the wording simply talks about the "area", not a barrier.
Has anyone thought this through or seen a ruling anywhere?
Note: Given that I'm playing a 3-foot tall gnome, we decided that on subsequent castings I'd do two. One is the normal one and the other is an inverted on with a "floor" about five feet in the air, that extends into the earth. The overlap allows for protection.
Best Answer
Hemisphere: One 1/2 of a Sphere, a partial sphere. IE: Dome.
Unfortunately the intent* of the spell is in it's very first line. It creates a half spherical dome that appears (again emphasizing the precise RAW text here to avoid interpretation arguments) around and above you but not below you that barres creatures outside of it from passing through it. Since the magical walls of this barrier specifically do not extend below the caster, then anything capable of tunneling up through the ground or passing through the ground is fair game for entering your hut from the underside.
Let's hope a Buelette doesn't wander by!
*Finally officially explained here