In all districts, if a non-conforming building or other structure or other improvement located on land with minor improvements is damaged or destroyed by any means, including but not limited to, any demolition ordered or permitted by the Department of Buildings, to the extent of 25 percent or more of the assessed valuation of all buildings or other structures or other improvements thereon (as determined from the assessment rolls effective on the date of damage or destruction), such non-conforming use shall terminate, and the zoning lot shall thereafter be used only for a conforming use.