While auditing our loans, I have discovered loans where buildings have been added as "separate structures' on the property insurance. These were not on the property at the time our loan was closed. These buldings are not added to the flood insurance. Do we need to require flood insurance on these structures?

I would consider that a tripwire since it gives you knowledge. We would check into it and see what's what.

I agree. You now have knowledge of an uninsured building. You need to notify and begin force placement procedures.