D.C. Mun. Regs. tit. 8-B, § 1302
1302.1 Employees may accrue unused vacation only to a maximum of two hundred forty (240) hours in a leave year.
1302.2 Any carry-over of unused leave beyond two hundred forty (240) hours shall be requested through the immediate supervisor and approved by the President or his designee.
1302.3 Carry-over of unused vacation leave shall only be approved when the reasons for the carry-over are related to work priorities.