
My guess is that the 195-unit mixed-income
Lofts at Capitol Quarter residential project is the current holder of the title of Longest Building Under Development, and while that could refer to the
years it took to get the dang thing financed, in this case I'm describing the footprint of actual construction, running westward from 7th and L for what seems like forever.

The eventual height of the DC Housing Authority building has become clearer in recent weeks with the construction of the elevator shaft/stairwells, but while the rendering of the finished product gives some sense of the size, it's hard to adequately capture in photographs at this stage its length along L Street, especially since it also runs downhill.
But give me credit for at least trying, with shots from all four corners, though admittedly one is actually a stiched-together image of two photos from the southwest side. (Can you tell which one?)