The tax exemption or deferral for the dwelling that otherwise would have been provided under the local ordinance shall be prorated by multiplying the amount of the exemption or deferral by a fraction that has as a numerator the percentage of ownership interest in the dwelling held by all such joint owners who are at least age 65 or (if provided in the ordinance) permanently and totally disabled, and as a denominator, 100 percent. As a condition of eligibility for such tax exemption or deferral, the joint owners of the dwelling shall be required to furnish to the relevant local officer sufficient evidence of each joint owner's ownership interest in the dwelling.
Va. Code § 58.1-3211.1