To authorize upon appeal in specific cases such variance
from the terms of this chapter as will not be contrary to the public
interest where, owing to special conditions peculiar to a specific
property, a literal enforcement will result in practical difficulty
or unnecessary hardship so that the spirit of this chapter shall be
observed, public safety and welfare secured and substantial justice
done. Except as specifically provided, no action of the Board of Appeals
shall have the effect of permitting in any district uses prohibited
in such district. Where a variance from these regulations has been
granted by the Board of Appeals, the minutes of the Board shall affirmatively
show that an unnecessary hardship or practical difficulty exists,
and the records of the Board shall clearly show in what particular
and specific respect an unnecessary hardship or practical difficulty
is created.