D.C. Mun. Regs. r. 3-413
Except as provided otherwise in this section, a party may amend his or her pleading only by leave of the Board or by written consent of the adverse party.
A party may amend his or her pleading as a matter of course at any time before a responsive pleading is served.
In all cases except petition challenge cases, if the pleading is one to which no responsive pleading is permitted and the action has not been scheduled for a hearing before the Board, a party may amend it at any time within twenty (20) days after it is served.
In a petition challenge case, if the pleading is one to which no responsive pleading is permitted and the action has not been scheduled before the Board, a party may amend it at any time within two (2) days after it is served, provided however that amendments filed after the close of the challenge period cannot expand the basis of any timely filed challenge.
In all cases except petition challenge cases, a party shall plead in response to an amended pleading within the time remaining for response to the original pleading or within ten (10) days after service of the amended pleading, whichever period is longer, unless the Board otherwise orders.
In a petition challenge case, a party shall plead in response to an amended pleading within the time remaining for response to the original pleading or within two (2) days after service of the amended pleading, whichever period is longer, unless the Board otherwise orders, provided however that amendments filed after the close of the challenge period cannot expand the basis of any timely filed challenge.
D.C. Mun. Regs. r. 3-413