The value of real estate as ascertained at a general reassessment and the ascertained value of new grants which may hereafter be entered and assessed shall only be changed to allow the addition of the value of improvements, or a total or partial deduction of the value of such improvements or an addition to or total or partial deduction from the value of the real estate caused by any easement affecting the real estate, except so far as the same are directed to be corrected by a court of competent jurisdiction or by the local board of equalization in the exercise of powers expressly conferred by law. Routine maintenance shall not be considered as improvements.
Va. Code § 58.1-3351