Where official approval has been granted and valid building permits have been issued prior to the effective date of this chapter or any amendments thereto, the structures may be completed and used in accordance with the plans and specifications upon which such building permits were granted; provided, construction is commenced within 30 days after the issuance of the permits and work is diligently pursued to completion within the subsequent six month period and not discontinued until completed except for reasons beyond the builder's control.
('64 Code, § 51.07)