Painting London’s rooftops white could help reduce the outdoor temperature of the city by up to 3.6 degrees Fahrenheit (2 degrees Celsius), according to a new study that investigated the most effective ways to cool the U.K. capital.

Problem is that I bet that they also don’t look great, as grime is gonna be a lot more visible.

You can wash them, but then you’re gonna need to send someone up there with a pressure washer on a regular basis if you want it to be pristine.

kagis

This guy is talking more about the functional than the aesthetic, that you need more maintenance on a light roof:

https://www.roofingcontractor.com/articles/91038-the-dirty-truth-about-white-roofs

There is, however, another aspect to low-slope roof maintenance in the era of the cool roof. You must keep them clean if you expect to take advantage of the reflective properties of a white or lightly colored membrane.

If the person expected to buy a new, bright-white reflective roof to last two of the expected 20 years of service life, then I haven’t much of a point to make.

Maybe it’s possible to use some sort of light-but-not-white pattern that hides some of the grime and lichens and such. That won’t help the roof functionally, but it might make it more aesthetically appealing.

Maybe smoother and steeper surfaces could be less-prone to long-term grime buildup, tend to be washed better by rain alone.