Can one enter Leomund's Tiny Hut from below?

Question

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.

Answer 1

Leomund's Tiny Hut

Range: Self (10-foot-radius hemisphere)

Hemisphere: One 1/2 of a Sphere, a partial sphere. IE: Dome.

...A 10 foot radius immobile dome of force springs into existence around and above you and remains stationary...

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

Answer 2

Right now it has a floor

RAW is undefined, because dome is undefined

Dome and hemisphere are not defined in the spellcasting section (PHB p201), unlike cone and sphere. A hemisphere might be something very clear for a mathematician, but the game was designed by laymen for laymen. No mathematician would agree with the game's definition of line either.
Until an errata comes out on this, no one really knows if a hemisphere is supposed to have a floor or not, not even the game developers:

• Jeremy Crawford, 2016-12-05
• Jeremy Crawford, 2017-01-23

The latest tweet says it has a floor, but its arguments are as (un)convincing as the previous one's.
So right now it has a floor

Play the way it makes sense, independent from any tweets

A new one might come out in the middle of your next gaming session anyway.

Balance

The intent of the spell is indeed to keep the enemies out, and the majority of the monsters, if not straight out possessing a burrowing speed or phasing ability, is smart enough to dig. IRL dogs have dug under fences to get to the chickens, and they have an Intelligence of 3 in the game. This is setting the bar pretty low.
If it is that easy to get in, you still have to keep a sentry inside. Not what you expect from a 3rd level spell, I would not even take it in a 1st level slot.

Logic

Another consideration is the sentence about the weather:

The atmosphere inside the space is comfortable and dry, regardless of the weather outside

If you set it up in a muddy field, during rain, how could it be dry without a floor?

Geography

If you are in the mountains, or on a hillside, not having a floor leads to hilariously silly results. Sometimes it is not possible to find even ground for hours. Carrying around a shovel is not only embarrassing for a powerful wizard, but digging in hard rock or frozen ground is close to impossible.

In-game history

Leomund is a renowned archmage, why would he create a protective spell that does not really protect?

History of the game

In previous editions, it always had a floor (SRD)

Conclusion

RAW is flexible, now it has a bottom.
But it may change soon again, so I suggest to keep playing the only way it makes sense; with a bottom.
Otherwise Leomund's Tiny Hut is a silly, seriously underpowered spell, which is next to useless except in ideal, rare conditions.

Answer 3

Mathematically, a sphere is usually a solid object if not specified as hollow of solid. This makes me assume that a hemisphere is a solid sphere cut in half and thus also has a floor.

If you go by the letter of the spell, as Airatome did, then there is a point to be made to it being a hollow half sphere (i.e. a dome) and thus that there is no floor. You can also argue that you cannot be in an object of solid force.

A final way to look at it is in the game's perspective. It is a 3rd level spell, quite high, so it should be on par with lightning bolt, fireball etc. If anyone can dig underneath or move underneath (like wraiths) a lot of the protection is lost.

DnD 5e is not written to be over-descriptive but to be fairly easily understood. Most importantly is that a clear answer is chosen by the DM, so you know the spell will act the same every time.

Answer 4

The dome protects you from below.

There are two things that are both called domes.

There is a mathematical shape - a dome. There is an architectural thing, also called a dome because it looks vaguely similar to a dome.

Note that the volume equation here demonstrates that a dome is a solid, similar to a hemisphere. That equation would not work if a dome was a thin shell.

As the spell description uses hemisphere, and dome, there is no way to interpret it as "a thin hemispherical shell with no floor". If they wanted that shape, they would need to use that phrase.

As for the "around and above you". That doesn't imply a thin shell either. You occupy the 5 ft square you are in. The spell effects the squares around (at ground level) and above (up to 10 ft high) you, which is consistent with a hemisphere/dome.

tl;dr Your DM is an architect and their interpretation of the term dome is understandable but incorrect in this case.

Answer 5

The text of the 3rd-level Tiny Hut spell (SRD p185) gives its range as "10-foot-radius hemisphere" and states: "A 10-foot-­radius immobile dome of force springs into existence around and above you" (my emphasis). It does not exist below you, therefore it cannot include a floor.

The spell includes the line, "The atmosphere inside the space is comfortable and dry, regardless of the weather outside" (my emphasis). An argument that this implies a magical floor is spurious. It does not even imply that the ground beneath the dome is dry, as it is limited to the "atmosphere". It merely suggests that the dome is akin to a large magical umbrella.

The 5th-level spell Wall of Force (SRD p187) allows the caster greater control over the shape and position of the protective barrier generated, including "a hemispherical dome or a sphere". This spell also allows the user to create the effect "in any orientation you choose", which is not permitted by Tiny Hut, ruling out your new tactic.

The limitation on the 3rd-level spell appears to be a deliberate design choice. If you want stronger magical protection, use stronger magic.