I believe that there should be a clear separation between an original historic building and an addition to that historic building. I happen to strongly prefer traditional additions onto historic buildings, but I consider my style preference to be personal, and not something that should be dictated by historic preservation guidelines or zoning codes.
I want to see the historic building as its own entity expanded by what is obviously a later addition. I do not want to see a historic building with an addition with brick toothed in and a new seamless roof over the entire building. This misleads future observers of historic buildings into believing that the building was originally built that way. It waters down future observers’ understanding of the integrity of historic forms and construction methods.