Ask Kevin: Roof color quandary
23 May '07 from Kevin Contreras
Kevin,
I plan to build a straw bale home within a clearspan steel building in the Olympia, Washington - Portland, Oregon area.
The den and dining areas will be on open decks in the plaza and the plaza will have a Japanese garden with a Koi pond. But, the question is of roof color. Is it cheaper to produce solar heat to heat or thermal cooling to cool the building? In other words, should the standing seam metal roof be white or silver, or dark in color?
Danny
Danny,
This sounds like an interesting project, although I can’t quite visualize what you’re up to. There is always a quandary about heating and cooling the building. We want the sun to heat the building when it’s cold outside and yet keep from heating it when it’s warm out. Ideally, in the winter everything including the roof would be dark colored and un-shaded during the day, to soak up as much heat as possible. Then, it would be wrapped up in a big blanket at night to keep all that heat in. In the summer, it would be insulated, light in color and shaded to protect from any heat absorption. So, what do we do?
The simple answer is:
1. Insulate the walls and ceiling very well to keep the temperature from being affected greatly by changes in outdoor temperatures.
2. Make sure all windows are dual pane to let in natural light while accomplishing the same as the insulation.
3. Put a light colored roof on the house. Since you are insulating between the roof and the interior, any heat gain on the roof is only going to create what is called the Heat Island effect, where sun is absorbed and released to heat the atmosphere unnecessarily.
Good Luck!
Kevin
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Solar roofing
In Southern, Ca. there is not much need for heat, other than heating water or clothes drying. However, across the state as a whole, the US Energy Information Adminstration data http://www.eia.doe.gov/emeu/recs/recs2001/ce_pdf/enduse/ce1-7e_4popstate... indicates that the average California household spends 3.7 times as much on space heating and water heating combined as it spends on air conditioning. Nationally heating is even a bigger percentage of household use (New York spends 8 times as much on heat as AC).
For these heating dominant homes, there is an additional way to greatly increase the solar energy you can recieve from a dark colored conventional metal roof. We have emloyed this technique on several projects, including commerical, residential, and government. (See Solar Today magazine Jan/Feb 2007)
You simply have to capture the solar heated air from the underside of the metal roof panels. If the roof deck is open, (steel beams), install a radiant barrier film below it to create an air space, then duct that heated air down to the building, using a solar fan and controller.
You can use the solar heated air for space heating, water heating, clothes dryer preheating and combustion air preheating. This will save energy and money all year long. The radiant barrier will block most of the heat from the roof in the summer air conditioning season.