The components section for forbiddance says:
V, S, M (a sprinkling of holy water, rare incense, and powdered ruby worth at least 1,000 gp)
This does not explicitly state that the spell consumes them, which is the norm for spells that consume their material components.
However, the spell also states:
If you cast forbiddance every day for 30 days in the same location, the spell lasts until it is dispelled, and the material components are consumed on the last casting.
This got me wondering if this means the material components are only consumed at the end of a 30-day casting, or whenever you do not cast the spell in the same place the day after casting it last?
Best Answer
At the same time that the spell becomes permanent until dispelled.
Spell components are only consumed when explicitly stated.
The wording is pretty clear - "If X, then Y and Z". X is casting it daily in the same location for 30 days, which leads to the spell becoming permanent and the material components being consumed.
If you don't cast forbiddance for the full 30 days and stop early, the components won't be consumed.
Sure, you can argue that the sentence is ambigous, but D&D 5e is not as logic-defying as previous editions sometimes are. It uses regular English language, and it wouldn't make any sense for the material components to be consumed before it becomes permanent. Otherwise, a single casting could be counted as progress towards 30 days - meaning that the components would always be consumed.