The planning commission may authorize variances from the requirements of this title where it can be shown that, owing to special and unusual circumstances related to a specific piece of property, strict application of this title would cause an undue or unnecessary hardship, except that no variance shall be granted to allow the use of property for a purpose not authorized within the zone in which the proposed use would be located. In granting a variance, the planning commission may attach conditions which it finds necessary to protect the best interests of the surrounding property or neighborhood and otherwise achieve the purposes of this title.