The fire, which occurred on April 30, 2007 (the same day Eastern Market burned down), was allegedly caused by heat guns that were being used to strip lead paint off the building’s exterior during renovations. The blaze caused extensive damage to the library, which also housed an extensive collection of historic documents about Georgetown (most of which were luckily able to be saved).
Design work and reconstruction began in the spring of 2008. According to the We Love D.C. post, the projected opening date is being advertised on construction signs at the site.
Photo from Flickr user randomduck, used under a Creative Commons license.