Can Forbiddance affect multiple floors of a building with a single casting?

Question

Forbiddance says:

You create a ward against magical travel that protects up to 40,000 square feet of floor space to a height of 30 feet above the floor. (D&DBeyond)

Say I have a modest but cushy multi-floor fortress with a hero-teleportation problem. Assume that there are at least two separate floors that I want to cover that are more than 30 feet above/below each other.

Could I use one casting of forbiddance and divide the 40,000 sq. ft between multiple floors?

Say I have a small shed that my gardener uses to tend to the hero-eating plants around the perimeter of my fortress. It is not connected to the main building and is, say, 100 feet away from it.

Could I cover the shed (or any other area not contiguous with the others) as well with that same casting?

Assume throughout that the total area covered would be less than 40,000 sq. ft.

Answer 1

Yes, you can spread the area out over non-regular interior spaces.

The thing that immediately draws my attention about Forbiddance is that it doesn't specify a radius. It says it affects "floor space." That form of measurement in D&D is used exclusively or almost exclusively to specify the interior of buildings, bounded spaces, and containers; giving a strong indication that the spell is intended to work inside the walls of a building regardless of shape. The explanation for why multiple floors can be covered continues below.

No, you probably can't cover a non-contiguous area.

The RAW doesn't definitively indicate the floor space must be continuous or contiguous -- or, for that matter, anywhere near you, except for one section which you touch when casting. Overall, that's pretty weird because other spells like Guards and Wards and the various Wall spells do. Conversely, spells that definitely do target multiple non-contiguous areas (like Meteor Swarm) also give their area placement rules fairly clearly. It seems like neither position can be taken as assumed.

The only clues here is that area is specified as a single block, and the casting time is more than sufficient to tour any regular polygon with that area. Given those, the 'local and continuous' interpretation is by far the most easily supported. Even read that way, however, you could use a narrow "pathway" to connect the two buildings so long as the 40,000 sqft area was sufficient. (How narrow? 5ft? 1ft? 1in? ...Ask your DM.)

Yes, you can cover multiple floors, so long as they're connected by "floor."

In any case, changes in elevation absolutely can be contiguous (and usually are), and the spell seems to support this feature. Casting Forbiddence in a building on a hill would by RAW and should logically cover the entire floor area, even if it's not level. For the same reason, any floors connected by flooring (like staircases) can simply have the contiguous space spread upwards over them and onto the next floor.

The caveat here is that technically, one could call a staircase non-continuous flooring, since you can't actually walk on the rise of a step. Of course, there's a solution here too: access ramps. (For magic.)

Answer 2

I would say no to both questions. The spell has a height of up to 30 feet above the floor it is cast-upon, that is what I would use for covering multiple floors with one spell. It would also be very confusing, for the following reasons:

1.) How does it interact with magic negation, such as Dispel Magic? If I successfully Dispelled one non-contiguous area covered by the spell, would I Dispel the entire area affected by that casting, or just the area targeted? The former seems like it would make the endeavor meaningless, since the villain would get better protection from multiple castings. If I could only Dispel the area targeted, then what prevents the villain from putting 480,000x 1 sq. in. squares with only 1/2 inches between the individual squares? Would I have to run-around casting Dispel Magic 480,000 times?

2.) How would this interact with casting and components? The spell has a static casting time which does not change with the area covered. Allowing non-contiguous areas to be covered would increase the area that can be effectively covered while having the same casting time. So, to cover 480,000x 1 sq. in. squares would have the same time and component costs as to cover 1x 40,000 sq. ft. square.

3.) What if one of the areas moves? What if I target a pallet or stone block that is being used as a floor, and then that block or pallet gets moved? Does the spell move with it? Or does it stay there? If it stays, does it remain in the same area and height where it was cast, or does it move to the closest "floor" space below the area that the pallet or stone block once occupied?

I would rule that, for every single casting of Forbiddance, you can create one area, which can be up to 40,000 sq. ft. by 30 feet. Multiple, non-contiguous areas would require separate castings of the spell.