Now it gets interesting. I went looking for the study done in Florida that I read just a month or so ago. I found the same study again, or I should say part of it. The original study that I saw consisted of instrumenting and monitoring the energy usage of 6 side by side houses in FL that were identical except for the roof type and/or color. As I posted earlier, the study showed that on a yearly basis, having a white shingle roof versus a dark grey one resulted in a 10.8% reduction in energy usage.
But here is the interesting part. That 10.8% number is with the houses set at 77F and UNOCCUPIED. In the SAME study, when I previously saw it, it also contained a section on the results when the homes were then monitored OCCUPIED, but with the thermostats still set at 77F. And when occupied, the yearly energy savings dropped to just a few percent. The reason for that is obvious. The amount of energy saved by the white roof is going to be the same whether occupied or unoccupied. But when occupied the energy usage overall is going to be higher, due to opening doors, cooking, appliances, etc. So the percent savings of the actual energy usage is going to be a lower percentage.
It's interesting that part is gone. Now why might that be? Maybe it's because it's too real. I'm getting a new roof and was curious about the difference between a grey or black shingle. When I saw that in a real house, in FL of all places, going from dark grey to white only resulted in a few percent savings, I said forget it, the difference between black and grey isn't going to matter. And keep in mind that is for FL. I'm in NJ and in northern climates, what you save in summer is partly offset by increased heating costs in winter......