Yet another photo off of a rooftop, this time on the Upper West Side. You can’t really tell from this angle, but those buildings are all ten to thirteen stories high, and they’re all steel-frame with brick curtain walls. We’re looking at the rear facades, facing the interior of the block.
First, most of these buildings have red, brown, or dark-gray brick facing the street, where they have their “for show” ornamented facades. The yellow brick and brick painted white on the rear are an effort to bounce light around, to get more daylight in the rear-facing rooms.
The most important thing in this picture is the presence of clean-brick stripes on those rear facades, some horizontal and some vertical. The vertical stripes are typically at the corners and the horizontal stripes are typically centered on the floor elevations, and those two facts point to what’s been going on. The structural-steel frames of these buildings, constructed for the most part in the 1910s and 20s, are rusting at the perimeter. The steel was not waterproofed in any modern sense, although it was protected by several coats of red-lead paint and, to a lesser degree, by the alkaline mortar. As the spandrel beams and the corner columns rust, they push the brick outwards (since rust occupies a larger volume of space than the steel it came from) and the resulting cracks and bulges in the masonry are the symptom that leads to investigation of the problem. The replacement brick is cleaner than the old brick, and that’s why we see the stripes.
The stripes are in essence scars, and each tells us one thing: the wall was opened up here. They don’t tell us what else was done: was the steel repaired? Replaced (although that’s rare)? Looked at and then covered up with new brick because it was good enough? Was new waterproofing installed to prevent a recurrence of rusting? If we’re lucky we have reports and drawings telling us the intent of the previous work; if we’re extraordinarily lucky, we might have photos. Usually we have not much other than the stripes (or, of course, their absence) to tell us where problems were investigated in the past.
