Roofs in New York used to be black. The usual and partially-accurate phrase to describe the waterproofing was “tar and gravel” and tar is black. The picture above, of a bunch of old tenements in Alphabet City, show where we are now: silver roofs!
This is not a small thing and is the direct result of an NYC legal requirement, Local Law 21 of 2011. (Similar laws have been enacted elsewhere, some before NYC’s. I’m talking about conditions here because that’s what I’m most familiar with.) The short version is that cities have what is known as the “heat island effect” and roofs that reflect light reduce it. Replacing nature (grass lands, forest, wet lands, and so on) with materials that can absorb and store a lot of heat (concrete, masonry, asphalt) is part of the problem. Replacing relatively light-colored nature with black roofs is another. Using reflective roofs sends some of the heat back into space, making the environment in general closer to what it was before the city was built, and making life better for the people in the top-floor spaces of the buildings.
This was the first step toward reducing the NYC heat island and it was not the last. We recently got a new regulation – Local Law 94 of 2019 – that will push us towards not having much generic roof at all. The new law requires roofs (on new buildings and to a lesser degree on existing ones) to be active terraces, used for photovoltaic solar power, or planted as green roofs. Green roofs not only reduce heat absorption, they increase water absorption and so reduce the amount of rain water dumped into our sewers.
I take an interest in these things, of course, because they have professional implications: except for silver paint, all of the measures discuss can increase the loads on roof structure, and so may require OSE’s involvement. But more importantly, reducing the heat island, reducing sewer run-off, reducing the power required for air-conditioning by increasing roof insulation, generating power on roofs…these are all relatively simple ways to improve the environment without ripping everything apart in huge projects. Maybe we need huge projects to improve the environment, but we can still improve things incrementally at the same time.
