Bloomingdale has one-story garages that abut alleys.
Bloomingdale also has a small collection of two-story carriage houses that abut alleys.
Of course, Bloomingdale has its share of pop-ups and pop-backs.
Bloomingdale has yet to have any new buildings constructed behind the main house (other than new construction one-story non-residential garages).
Both 20 Channing Street NW and 14 Channing Street NW -- which have extremely long lots -- are getting new construction 2nd buildings not physically attached to the main house (except for a "connecting" trellis.)
By providing a connection between the two structures, DCRA says it is one building. The "meaningful connection" is labeled covered by trellis.
The new building gets three stories and basement -- and a roof deck.
The new 2nd buildings to be constructed in the back yard will be residential and not garages.
It would appear that all of this work is matter-of-right. No zoning relief is needed, I believe.
New ground for Bloomingdale!
See these two PDFs:
20 Channing St NW Plat Plans for New 3 Story Separate Bldg 2017 03 12 by Scott Roberts on Scribd