The value of any building fixed as provided in sections 3964 and 3965 of this title shall be considered the true value of the building during the term for which any fire insurance policy is issued to cover thereon, if issued within three years from the date of such award, and such value shall continue as the basis of valuation for the purpose of ascertaining the amount of insurance required under a co-insurance clause until a new valuation has been made on an application by the insured or by the company, or agent placing the insurance thereon, provided that a new valuation shall not be required oftener than once in three years.