« Oh Henry (Gifford)... | Main | So it's a great house, how do your customers KNOW that? »
October 13, 2008
Green from the roof down
Up here in Montana we worry less about keeping our homes cool in the summer and we focus on keeping heat in during the winter. But for most Americans, hot summers mean high energy bills and keeping cool is key.
Many in the building industry have encountered the concept of what an Urban Heat Island (UHI) is and how it can create an additional burden for energy sources. The UHI is basically a term to describe how cities are generally warmer than the surrounding rural areas. Paved roads, sidewalks, and lack of vegetation contribute to making metropolitan areas significantly warmer year around.
As our cities begin to sprawl, this heating effect expands regionally with the new development. Though it may seem insignificant to the individual, when our neighborhoods get even a few degrees warmer on average, the energy used to cool our homes goes up exponentially.
According to an article published last month in the LA Times, one solution to this problem is to install reflective or white roofs. Unlike the traditional dark asphalt shingles found on most new homes, a white colored roof would send solar radiation back into space before it could be absorbed into the home and raise energy costs, as well as global warming.
Research at the Lawrence Berkeley National Laboratory suggests that if the largest 100 urban areas installed white roofs and reflective pavement it could offset 44 metric gigatons of greenhouse gasses.
To be honest, I have no idea what that means, I'm not a climatologist. But when breaking down the numbers, scientists say that reflecting that much heat back into space could give us a 10 year jump on managing climate change. Already California has started to require new commercial roofs to be white, and next year even residential building code will mandate similar energy-saving rules.
It never ceases to amaze me that some of the most difficult challenges of our times can be solved by simple, practical solutions.
Posted by Andrew Hunt at October 13, 2008 4:41 PM
Trackback Pings
TrackBack URL for this entry:
http://blogs.scrippsnetworks.com/cgi-bin/mt/mt-tb.cgi/1659
Comments
I live in Arizona, and I can personally vouch for the energy-erducing effect of reflective materials. In my 2-bed addition, I used radiant barrier OSB for sheathing under a sand-colored metal roof. The temp in the existing attic in the fall/spring (entering the attic in summer is out of the question) would be enough to cause excessive salt-in-the-eyes sweating in a matter of minutes. Turns out the old roof was 2-3 layers of asphalt shingles hidden under a metal roof, causing heat to radiate downward out of the shingles, extending the cooling season. The attic in the addition is possibly cooler in the height of summer than the old attic was in the shoulder seasons. The result is that I am able to reduce the cooling season by weeks on both ends.
Posted by: thaxman at November 3, 2008 8:34 PM
Certainly lighter roofs can affect the UHI of an area, but the most direct and tangible benefits are for the homeowner. As thaxman mentioned, using a radiant barrier in any practical way can seriously reduce the amount of heat gain in a conditioned space.
Out here in the mid-Atlantic, we have a lot of 50+ year old colonials, ramblers, and cape-cods. Most of the interior heat gain on the 2nd floor is due to heat radiating off the ceiling, not from 1st floor convection, meaning that adding the radiant barrier in the attic area can not only affect the cooling load typically by 10 to 20 percent, but also the heating load in the winter, due to the heat being radiated back into the space (depending on it's installation).
Physically, the internal temp of an attic space before installing the radiant barrier can be around 190 degrees. After the job is done, the attic is at about 110-115.
Posted by: Matt Dirksen at November 21, 2008 10:55 AM
