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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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