Anatomy of a Green Building - Lesson 8 - White Roof

Thursday, October 13, 2011
By Matt Sutter, Chief Executive Officer
In Sustainability

To white roof or not to white roof, that is the question. Back in his day, Shakespeare did not have that option, but today we do. I have been asked many times about whether a white roof leads to lower energy usage as compared to a black roof. The answer is: It depends. It depends on several factors.

In the Northeast Ohio area, where we are building our new building, the winters are harsh. From October to May the nights are below 50 degrees and the days are usually 65 degrees or less. That is 8 months of the year where the outside temperature is less than the ideal indoor temperature. This would seem to make the case that a black roof would be a good choice because the sun should heat up the black roof and keep the building warm. This is the essence of the debate in northern climates.

In southern climates such as Florida or Arizona, white roofs are without question the way to go. With summer temperatures well over 100 degrees and winter temperatures in the 70s, buildings in these climates are all about keeping the occupants cool. With its high level of reflectancy, a white roof can reduce the temperature on the roof by a whopping 80 degrees, and significantly aid in reducing the air conditioning load on the building.

Back to the northern climate debate. In Northern climates it depends on the type of building and its use. For example, a multi-story office building actually needs to be cooled for about 10 months of the year. This is due to the fact that people, computers, lights, copiers etc... within the building all create heat and warm up the building. This creates the need for air conditioning, and ways to reduce heat. Schools in a northern climate may be a different story. If the school building is only a single story and is used primarily in the winter time, there may be more need for heating than cooling.

So it depends on the individual circumstances of the building. The US Department of Energy has put together a simple program that you can use to examine your building. Go to the following DOE link and enter the requested data to see if a white roof is right for you:

http://www.ornl.gov/sci/roofs+walls/facts/CoolCalcEnergy.htm

*Note that the DOE program does not take into account the use of the building and whether the building is predominately in heating mode or cooling mode. Seek out your favorite Green Architect for a more detailed analysis.

For the SōL Harris/Day office building, it was determined that the building would be in cooling mode 10 months out of the year. This led us very quickly to a white roof solution. Through energy modeling, it was determined that we would save approximately 8% on our energy costs by using the white roof. The white roof should also last longer as summertime temperatures on the white roof will be about 100 degrees F in lieu of a black roof temperature which can reach 180 degrees. The white roof is a nice solution to both energy savings and longevity of the roof.

Matt Sutter
SōL Harris/Day Architecture
msutter@harrisday.com
330.493.3722


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