The recent push in NYC and elsewhere to make roofing membranes white, must have been thought of during the summer. Because in the winter, black is the way to go.
My recent investigations of roof deflections due to snow accumulation yielded an interesting observation….white roofs had more snow on them than black roofs. Even in a literally ‘side by side’ situation of white versus black….the white roof had more snow.
We know that the color white reflects heat and the color black absorbs heat, so it stands to reason that in the winter, snow will accumulate faster on a white roof, since there is little or no latent heat. A sunny day after the snow event would require the solar energy to penetrate more snow depth on a white roof than a black roof. And, since most melting begins at the edges, this can’t happen on a white roof since the membrane is turned up the parapet.
The National Center for Atmospheric Research predicts that in the summer, entire metropolitan areas can be cooled 1 degree Fahrenheit, if white roof s are installed. “Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat,” Keith Oleson, the lead author of the study said.
But if you read the study further you find a caveat. White roofs are beneficial in the summer, but this benefit could be offset by higher heating costs in the winter. Did anyone consider the added snow load? What about a membrane that changes color depending upon the temperature?