The board of supervisors of any county wherein there is located a municipality described in Section 17-21-5 may, in its discretion, exempt from any or all county ad valorem taxes, excluding ad valorem taxes for school district purposes, for a period of not more than seven (7) years, any privately owned new structures and any new renovations of and improvements to existing structures where an exemption has been granted by the municipality in accordance with the provisions of Section 17-21-5. The exemption from county ad valorem taxes may be granted only upon written application to the board of supervisors of the county by any person, firm or corporation claiming the exemption. A copy of the order of the governing authority of the municipality granting an exemption from municipal ad valorem taxes shall be attached to the application as an exhibit thereto.