Va. Code § 58.1-3293
When from natural decay or other causes any previously assessed building and enclosure as aforesaid, is either wholly destroyed or reduced in value below $100, the commissioner shall deduct from the charge against the owner the value at which such building and enclosure may have been assessed; and if the value of the building has been impaired by violence to the extent of $100 or more, the commissioner shall assess the building in its present condition and reduce the charge for the same to the amount so assessed. When any timberland heretofore assessed, the owner of the timber on which is also the owner of the land, is reduced in value to the extent of $200 or more by the removal of the timber therefrom, the commissioner shall assess the land in its then present condition and reduce the charge for the same to the amount so assessed.
Va. Code § 58.1-3293