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Shingle Color
Name: Jon
Status: Student
Grade: 4-5
Location: MN
Country: United States
Date: April 2007
Question:
For my science fair project I wanted to see if color
effects the internal temperature of a structure. I built a model of a
house out of matte board, and painted the roof and sides each a different
color. I found that the house painted gray was the warmest, followed by
blue. When manufacturers create roofing materials or shingles is this why
they are about the same colors?
Replies:
Hi Jon,
Energy from the sun is primarily in the invisible infrared
wavelengths, and in visible light. Color has nothing
whatsoever to do with an object's ability to absorb infrared
energy. That is because color is a property related to
visible light only. White paint, for example, appears "black"
to infrared energy. That is, although it reflects most
visible light (which is why you see it as white), it strongly
absorbs infrared energy. In fact, most surfaces except bare
polished metal, strongly absorb infrared. A significant part
of the sun's energy is in the infrared region, so no matter
what color your experiment was painted, it looks black to
infrared energy. Almost all paint strongly absorbs infrared
regardless of color.
This leaves the energy in the sun's visible light. A
surprising amount of energy in the sun's output is in the
visible region; light that you can see. The reason that an
object painted black gets hotter than one painted white is
that the black object absorbs both infrared and nearly all
visible light energy too. A white-painted object reflects the
energy in the visible region, and mainly absorbs infrared
only, and so a white object absorbs less total energy.
Different colors of paint in your experiment all absorb much
the same amount of the sun's infrared spectrum, but they
absorb differing amounts of the visible light. Your grey
paint absorbs a large proportion of all visible light (which
is why it looks grey and has no particular color). The blue
color you used likely absorbs a fairly wide part of the
spectrum as well (especially if it is a darker blue), hence
very little of the visible spectrum is reflected away. Other
colors you tried may have been lighter (thus reflecting away
more of the visible light), or may absorb less of the total
visible light spectrum, reflecting the rest away.
Regards,
Bob Wilson.
Looking at this from a little different respective, I worked in the
roofing industry for 25 years and I can say that shingles are more often sold
for their ability to blend pleasingly with the house and outside
environment and with some concern for its reflective quality or heat transferring
ability. Most roof shingle colors perferred by customers have granules that are
darker with the exception of the common white granules shingles, but even
in this case, the underlining material these white granuales are placed upon is
black asphalt. Darker granulated shingles are preferred by many in my area
(43-45 degree north latittude) as to assist with snow melting in the winter,
however, I have not seen too many differences with the rate of snow melt with
the white shingle.
Furthermore, the impact of the house color and roof color to internal heat
is minimized today because of the high insulation ratings of the attic and
house wrapping materials used in modern construction.
One point about blue as a color. Blue granualted shingles and blue house
paint pigments are notorious for bleaching out to gray over time. House paint
has seen improvements with blue pigments, but granualed shingles are exposed
to UV rays constantly and tend to bleach out to a gray tone.
I am not sure any of this is helpful, but it may help you with your project's
discussion.
Steve Sample
First, I love your thought process. You made an observation (you saw that
roof color is similar from place to place), then formulated a hypothesis
(that color affects the temperature in a structure), and then designed an
experiment to test the hypothesis. That is terrific science! Well done.
Color can affect how much a surface heats up, as you data showed. However,
in the case of shingles, the color may play a minor role. There are many,
many layers in a roof (and typically a ventilated attic below the roof).
These other factors probably affect temperature in a structure more than
color. However, if all else is equal, color does matter! Black shingles will
be hotter in the sun than (otherwise equivalent) white shingles. That said,
shingles are designed to resist all sorts of weather, from hot sun to heavy
snow to driving rain. Even if their colors differ, their overall performance
is very consistent.
The most important reason for different colors of shingles (you can get
black, light gray, blue, red, brown, green, and on and on) is because people
want to have a shingle that matches (or complements) the colors of their
house. As an example, we had a hail storm where I live recently, and
everyone in the neighborhood got a new roof. Before the storm, everyone had
the same flat black roof. After the storm, people chose all different
colors, shapes, and sizes. Personal taste seemed to be the biggest factor!
As a next step, you could ask a roofing company to donate shingles of
different colors to you. They often have extras. You could repeat the same
experiment and see if shingle color, not just painted color, makes a
difference.
Hope this helps,
Burr Zimmerman
What guides a manufacturer is difficult to say. I suspect "energy efficiency" is
not near the top of the list -- not because they are "anti-environmental" but
the VISIBLE color plays a minor role in the absorbance of the roofing/siding.
Two factors that a likely (in the absence of any data) to be of more importance
is the absorption of infra-red radiation (heat radiation) and reflectance. A
shiny black surface could absorb less light energy than a "dull" white surface
if a large fraction of the incident "light" is reflected before it is absorbed.
It is also important to make sure that the thickness of the painted film and the
angle of incidence of the light are both taken into consideration.
This is a much trickier experiment than it appears at first.
Vince
Calder
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