If the householder does not set apart any real estate as before provided, or if what he does or has so set apart is not of the total value which he is entitled to hold exempt, he may, in addition to the property or estate which he is entitled to hold exempt under §§ 34-26, 34-27, 34-29, and 64.2-311, in the first case select and set apart by the writing required by § 34-14 to be held by him as exempt under §§ 34-4 and 34-4.1, so much of his personal estate as shall not exceed the total value which he is entitled to hold exempt and, in the latter case, personal estate, the value of which, when added to the value of the real estate set apart, does not exceed such total value. For the purposes of this section, the exemption under § 34-4, or unused portion thereof, that is limited by such section to real or personal property used as the principal residence of the householder or the householder’s dependents may only be used for such property, and its proceeds as provided under § 34-20, and no other property.