When a property owner can show that his property was acquired in good faith and where by reason of the exceptional narrowness, shallowness, size or shape of a specific piece of property at the time of the effective date of the ordinance, or where by reason of exceptional topographic conditions or other extraordinary situation or condition of such piece of property, or of the condition, situation, or development of property immediately adjacent thereto, the strict application of the terms of the ordinance would effectively prohibit or unreasonably restrict the utilization of the property or where the board is satisfied, upon the evidence heard by it, that the granting of such variance will alleviate a clearly demonstrable hardship approaching confiscation, as distinguished from a special privilege or convenience sought by the applicant, provided that all variance shall be in harmony with the intended spirit and purpose of the ordinance.