The problem with the Census is that sometimes the street isn’t clear. For a moment I thought the Martz family lived in Truxton Circle on R Street. However, looking at adjoining pages I figured out what Ancestry.com decided was a R in R St was actually K. The other thing was that I found the owner of Square 0551 lot 0851 (a wood structure in Reeves Alley) in the 1933-34 General Assessment was a family tree that did not know he had children.
Looking at the land records Robert William Martz bought the property, listed as old lot 19 in 1932 from John W. Hile. Then in 1935 he died in Clarendon, VA at the age of 46. His widow, Ethel Marie Lewis Martz (1895-1977) appears to have sold the property in 1942 to Paul J. Bower, who then sold the property to Embassy Dairy in 1947.
Square 551 (bounded by R, Florida, 1st, Q and 3rd Streets) was a mix of residential and commercial properties. In the 1930s Robert W. Martz was a coal and ice man running his own business. Since this property was in Reeves Alley as far as I can tell this could have been used for commercial reasons related to his business.
He did live at times in Washington, DC but not in Truxton or the Shaw areas.
I mentioned I wish I could amend or add to the family tree that left the Martz’ childless. Robert Martz (1889-1935) was survived by 3 children at the time of his death, Robert Jr. (1918-1999), Marie Ethel (later Marie Graham 1920-1990), and Catherine Elizabeth (later Thorpe, 1922-2009).