The Department shall set child support at the amount resulting from computations pursuant to the guideline set out in § 20-108.2 in determining the required monthly support obligation, the amount of support obligation arrearage, if any, and the amount to be paid periodically against such arrearage. There shall be a rebuttable presumption that the amount of the award which would result from the application of the guidelines is the correct amount of child support to be awarded. In order to rebut the presumption, the Department shall make written findings in its order that the application of the guidelines would be unjust or inappropriate in a particular case as determined by relevant evidence pertaining to support for other children in the household or other children for whom any administrative or court order exists, or relevant evidence pertaining to imputed income to a person who is voluntarily unemployed or who fails to provide verification of income upon request of the Department, provided that income may not be imputed to the custodial parent because (i) a child is not regularly attending school, (ii) child care services are not available, or (iii) the cost of such child care services are not added to the basic child support obligation. In addition, a party’s current incarceration, as defined in § 8.01-195.10, for 180 or more consecutive days shall not be deemed voluntary unemployment or voluntary underemployment. Additional factors that may lead to rebuttal of the presumption shall be determined by Department regulation.