We are working on a project in an 1890s apartment building where part of the scope is changing the windows in the penthouse. Most of the building has very heavy brick and stone exterior walls, but the penthouse (which may have been built later) has walls that are mostly terra-cotta block. There is a large steel spandrel beam carrying the penthouse roof in the area where our work is being performed, and we have checked that the beam is capable of carrying all of the load in the area.
The windows are fastened to small structural-steel channels that run from the penthouse floor to the roof spandrel beam. They are nothing more than funny-looking mullions carrying the lateral wind load on the windows, but because they are structural steel they seem more important. We have checked that they are not posts carrying the spandrel beams three times: once to be sure we understood the structural framing, once at the request of the building management, and once at the request of the contractor. Simply put, those steel mullions look odd to modern eyes. They are in a location that, in modern construction, we could use light-gage studs or aluminum extrusions. People’s perceptions are influenced by the tools, materials, and systems they work with, and the more limited choices that existed in 1900 created structure that to us seems overly heavy.
The early investigation portion of a lot of our projects consists, in part, of getting into the mindset of a designer or builder in the past. It’s the only way I know of to not mis-read existing structure.
