a. The enforcing agency shall examine each application for a construction permit. If the application conforms with this act, the code, and the requirements of other applicable laws and ordinances, the enforcing agency shall approve the application and shall issue a construction permit to the applicant. Every application for a construction permit shall be granted, in whole or in part, or denied within 20 business days, unless the application is limited to the construction of a ramp designed to provide wheelchair access to a one or two-unit dwelling, and required for such access by a resident of the dwelling, in which case the permit shall be granted or denied within five business days. If application is denied in whole or in part, the enforcing agency shall set forth the reasons therefor in writing. If an enforcing agency fails to grant, in whole or in part, or deny an application for a construction permit within the period of time prescribed herein, such failure shall be deemed a denial of the application for purposes of an appeal to the construction board of appeals unless such period of time has been extended with the consent of the applicant. The enforcing agency may approve changes in plans and specifications previously approved by it, if the plans and specifications when so changed remain in conformity with law. Except as otherwise provided in this act or the code, the construction or alteration of a building or structure shall not be commenced until a construction permit has been issued. The construction of a building or structure shall be in compliance with the approved application for a construction permit; and the enforcing agency shall insure such compliance in the manner set forth in section 14 of this act. The commissioner, after consultation with the code advisory board, may, for certain classes or types of occupancy posing special or unusual hazards to public safety, establish regulations designating the department as the enforcing agency for purposes of approving plans and specifications. A municipal enforcing agency shall not grant an occupancy permit for any such class or type of construction unless the applicant submits appropriate plans and specifications certified or approved by the department. Upon submission by an applicant of such certified approved plans and specifications, the enforcing agency shall recognize the approval when deciding whether to approve the application for a construction permit.