In Betrayal at House on the Hill, there is a rule saying that you can't add a tile if it would close off the floor:
Can I Seal Off a Floor by Placing a Tile?
You can’t place a tile in such a way that it seals off a floor (that is, leaves no way to connect other rooms to that floor). If the only possible placement of a tile would seal off a floor, discard that tile and draw new ones until you draw one that leaves a free doorway. If all the remaining tiles for a floor would seal off the floor, then the person whose turn it is rearranges the floor until there are more free doorways.
However, some haunts require that a certain room be added, if it doesn't exist already. For instance, Haunt #46 (The Feast) says the following
If the Attic isn't in the house, search the room stack for it and put it on the upper floor. Then shuffle that stack.
It says a similar thing for the Dining Room as well.
What happens if adding one of these tiles would seal off a floor? The room needs to be there for the Haunt, so not adding it isn't an option. What happens?