If at the time of reinstatement in the terms of the reinstatement value clause of this policy the sum representing 85 % (eighty per cent ) of the cost which would have been incurred in reinstatement, if the whole of the property covered by such item had been destroyed, exceeds the sum insured thereon at the breaking out of any fire or at the commencement of any destruction of or damage to such property by any other peril hereby insured against, then the insured shall be considered as being his own insurer for the difference between the sum insured and the sum representing the cost of reinstatement of the whole of the property and shall bear a rateable proportion of the loss accordingly. Every item if more than one, of this policy shall separately be subject to this condition.