Va. Code § 25.1-218
Any person not already a party to the proceedings whose property, or any interest or estate therein, is to be taken or damaged, or who claims that his other property, or any interest therein will be damaged as a result of the taking and use by the petitioner, may be made a party to the proceeding upon filing a petition for intervention by leave of court (i) at any time prior to the beginning of the trial of the issue of just compensation, or (ii) in the discretion of the court, at such other times during the pendency of the proceeding upon such terms and conditions as the court deems proper, considering all the circumstances at that time. Such a person intervening in the proceeding shall be permitted to assert any claim or defense then germane to the proceeding upon such terms and conditions as the court deems reasonable and proper.
Va. Code § 25.1-218