Expiration of permits. No permit for the erection, razing, change, alteration or removal of buildings shall be valid or effective after one year from the date of issuance thereof and shall thereafter be void, unless the work authorized by such permit shall have been substantially commenced within one year from the date of issuance and proceeded with due diligence. One six-month renewal of a valid permit that is about to expire shall be permitted without additional cost to the applicant. If, however, the applicant has been delayed in proceeding with the work for which the permit was granted by reason of any reasonable cause not due to his own negligence, the permit may be renewed without additional cost to the applicant.