So nothing else is damaged?!
This place is going down....
Down to the ground....
Ashes, ashes...
That will be all that remains....
We all fall down.
That is a variation of that terribly sad song about the plague.
When I said "nothing else is damaged", I was assuming there were other buildings around this one and you wouldn't want to start a gigantic fire in the city; potentially killing many people and destroying buildings. Be wise with fire. It spreads with no check, and by the time the fire department would get there most of your "mental institution" would probably be gone. People are more important than your personal vendetta against a building.