In David v. David, released today, the Virginia Supreme Court addresses the question of the burden of proof in cases where a divorcing spouse owned separate property, but either that spouse or the other spouse contributed work to it during the marriage, and the other spouse claims that the work made it increase in value. The non-owner spouse has the burden of proving that the work was done and that there was an increase in value, but then, once that is proven, the owner spouse has the burden of DISproving that the work CAUSED the increase.
This decision exactly relfects a statute which already addressed this exact issue, Virginia Code Sec. 20-107.3 A 3 a, which says in part:
For purposes of this subdivision, the nonowning spouse shall bear the burden of proving that (i) contributions of marital property or personal effort were made and (ii) the separate property increased in value. Once this burden of proof is met, the owning spouse shall bear the burden of proving that the increase in value or some portion thereof was not caused by contributions of marital property or personal effort.
http://www.courts.state.va.us/opinions/opnscvwp/1122145.pdf