(1) Where, solely for the purpose of affording air-raid protection,— (a) there has been added to a hereditament any such room or part as is referred to in paragraph (1) in column 2; or (b) there have been made any such structural alterations or additions or improvements to a hereditament as are referred to in paragraph (2) in column 2; such an addition or improvement shall be disregarded in the valuation of the hereditament. |