Highly-reflective roofing materials can actually receive an Energy Star
rating if their solar reflectivity is higher than 65%. There is also a CRRC
(Cool Roof Rating Council) certification for products meeting the Title 24
mandates for
the state of California.
I have some very interesting anecdotal information about a membrane roof I
installed on my house last summer. I find this roofing material simply
amazing.
I have a two-story 130-year-old Victorian house with the typical mansard
roof. This means there is a nearly flat section in the middle of the roof
with steep slopes outside of this central section. The central section is a
square about 25 feet on a side. Each story of my house has 10-foot ceilings
including the attic. I have a permanent ladder in the attic that leads to a
hatch so I can easily get onto this "flat" section of roof even though it is
over 30 feet above the ground.
If you have ever dealt with a flat roof, you know it can be a problem for
leaks. My leak problems went away last year when I had an industrial
membrane roof installed using a white-colored Sure-Weld membrane
manufactured by Carlisle Syntec Incorporated. This roof has a typical solar
reflectivity of 87%. I suspect the pigment is titanium dioxide, but the
data sheets I have seen don't specify the pigment. Below are some
interesting things I have noticed.
[1] My garage roof has light grey (almost white) asphalt shingles. When the
summer sun shines on these, I don't want to be on the roof because it is too
hot. If I put my hand down on the roof, it burns. I also do not want to
work on the highly-reflective membrane roof on a sunny day for a completely
different reason... it is simply too bright. If you go up there on the
sunny day, very dark sunglasses are mandatory. It is incredibly bright. It
is not a specular surface, so it is not a like a mirror reflection of the
sun in your eyes. It is just an overall very, very, bright white. The guys
that installed it wore very dark sunglasses, but immediately had to remove
their sunglasses as they got off the roof, otherwise they couldn't see
through their dark glasses. They remarked that the brightness did
contribute somewhat to a falling hazard because you cannot see anything very
well other than the roof itself.
[2] I was up on the roof late one afternoon to paint some trim around the
hatch and around the edge of the roof. The roof felt only a little above
ambient temperature when the sun was on it. It absolutely was not hot. The
amazing thing was when the sun went down. The roof got cold. Not ambient
temperature... but cold. That white roof was radiating like crazy. I
thought maybe I was imagining it, so I got a digital thermometer and placed
it in contact with the roof and it was about 60 F when the ambient air
temperature was about 72 F. This made me rethink my thoughts about
blackbody radiators.
[3] Here is a link to some info about this roofing material...
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
1 University Drive
Bluffton, OH 45817
419.358.3270
edmiston@bluffton.edu