First - the Mall.
We've noted that the Mall will be redesigned, but in the meantime, the National Park Service is rehabbing it one bit at a time. Phase One is the center panels between 3rd and 7th Streets. Their intent is to "provide more sustainable lawn panels through use of sandy soil, irrigation and curbs delineating the edge of the grass panels," as well as provide for better irrigation and drainage. The dark pink areas on the map note where the Mall is closed for public access. Anticipated completion of this phase is late 2012, though all three phases will bring us into Fall 2016.
Second - the National Gallery of Art.
The folks over at Architect's Newspaper have the full story, but in short, the I.M. Pei-designed East Building (completed in 1978) isn't holding up as well as the West Building (completed in 1941). You might remember the fences around the building in recent months - those were to prevent large chunks of marble falling and injuring the locals (so we thank them for that temporary stopgap, at least). Now, 16,200 slabs of marble will be removed and replaced. Lest you think it's an easy job - each panel weighs 450 pounds. The building will remain open throughout the duration of the construction, but certain entrances may be closed. Check the National Gallery's renovation information page before you head over. Construction is expected to be complete in Spring 2014.