But as part of trying to answer a work-related question, I found myself looking at DC Building Permits on microfilm from 1892 to 1920something. Just a quick observation… the 19th century stuff is a lot of new buildings. But there are, and more so in the 1917 & up permits, permits for additions to pre-existing structures. In 1917 and thereabouts people where building kitchen additions, two story add-ons, new porches, steps, thus basically not leaving their homes in the pristine state the original builder had left.