W. Va. Code § 48-1-204

"Arrearages" or "past due support" means the total of any matured, unpaid installments of child support required to be paid by an order entered or modified by a court of competent jurisdiction, or by the order of a magistrate court of this state, and shall stand, by operation of law, as a decretal judgment against the obligor owing such support. The amount of unpaid support shall bear interest from the date it accrued, at a rate of five percent per annum, and proportionately for a greater or lesser sum, or for a longer or shorter time. Except as provided in rule 23 of rules of practice and procedure for family law and as provided in section 1-302, a child support order may not be retroactively modified so as to cancel or alter accrued installments of support.