Hello there!

I'm new to the Houzz community as I'm in the process of purchasing my first home, a Baltimore rowhouse.

I've wondered for a while about a pattern I've noticed. In Baltimore, it seems pretty standard to see (what appears to be) additions added onto the back of the original rowhome. Some look pretty uniform in length, like the ones on Barclay Street and E Lanvale Street in the (Google Maps) screenshot below, and others are less uniform, like the ones on E 21st street in the second screenshot.

What I'm particularly curious about, however, is that even in three-story rowhomes, these additions appear to only be two-stories high. Does anyone know if there's a reason for this? Regulation? Cost? Engineering/construction capabilities? Style/convention?

I've done a bit of Googling myself and was able to locate this guidelines document but it appears to be related to adding an additional story atop the home, and doesn't indicate whether there are local regulations that would explain the two-story additions to three-story rowhomes.

I've attached the screenshots below to demonstrate what I mean. For example, it's clear all the homes facing Barclay St on the map have these two story additions, except the end unit which looks as though perhaps the original home was that full length? I'm guessing somewhat based on the end unit on the cross street (Lanvale) also being that length. (The houses on Latrobe are all only two stories.)

Any knowledge/history of these rowhomes and additions to them that you can contribute would be greatly appreciated!