D&D 5E Forbiddance - Subject to Cover or Bunker Buster?

[scholz]

PCs pursuing a vampire to its crypt. They want to cast Forbiddance from the relative safety of being behind a couple sets of stone doors. Assuming the casting is not interrupted, would the forbiddance extend through the cover?
If not, it seems a challenge to do its primary function, protecting a building from intrusion (unless the building was only one room).
If so, it seems to provide a slow, but potentially lethal 'bunker buster' attack that could wipe out lots of monsters in a dungeon or building or similar place without the PCs even needing to see them or know exactly where they are. Timed with a Leomunds Tiny Hut (dropped just before spell is cast), it could be pretty effective.

 

[jodyjohnson]

Given the 10 minute casting time I'd rule that it includes 'walking the perimeter' of the area to cover and spreading the dust throughout. Without being able to visit the area's covered I'd rule it can't breech barriers (walls/doors).

 

[jrowland]

Given the 10 minute casting time I'd rule that it includes 'walking the perimeter' of the area to cover and spreading the dust throughout. Without being able to visit the area's covered I'd rule it can't breech barriers (walls/doors).

I agree. Pg 204 PHB "A Clear Path to the Target". The 10 minute casting is so you can, within 10 minutes, get a clear path to all areas covered by the spell.

That said, I would allow the caster to begin casting the spell as the party makes it way through the complex, potentially trapping, ore busting, the vampire at the end of 10 minutes. (I probably wouldn't allow each room to be under forbiddance as they move, eg, only at completion). Hope the caster can make all the Concentration checks!