41 C.F.R. § 302-7.4 – HHG shipments that include PBP&E that might exceed, or did exceed, the 18,000 pounds net weight allowance.

(a) The agency should separate the PBP&E and have the HHG carrier estimate the weight of the PBP&E before the HHG shipment is picked up. Subtract 110 percent of the estimated PBP&E weight (to adjust for packing materials) from the estimated gross weight as shown on the shipping documents (i.e., net weight minus the PBP&E minus 10 percent of the PBP&E). If the result is more than the 18,000 pounds net weight allowance, then the shipment exceeds the net weight allowance.
(b) If it was not discovered that the HHG shipment exceeded the net weight allowance in advance, and if the PBP&E was not weighed or estimated before shipping, then the agency should weigh the PBP&E before it is delivered. Determine if the shipment exceeds the net weight allowance by applying the formula in paragraph (a) of this section.
(c) If the calculation in paragraph (a) of this section shows that the shipment does not exceed the net weight allowance, then the agency may transport and pay for shipping the PBP&E plus packing materials with the household goods.
(d) However, if the calculation in paragraph (a) of this section shows that the shipment may exceed the net weight allowance, and if the employee was authorized PBP&E, then the employee must pay for shipping all weight that exceeds the net weight allowance for their HHG, minus the PBP&E and packing materials for both. The agency may then pay for shipping the PBP&E as an administrative expense.
(e) The agency may require reasonable documentation of the items requesting to be shipped as PBP&E and the weight of the PBP&E.