What is roof reflectivity? – Important facts to consider
In a previous article we talked about the energy implications of roof systems and the type of coating and membrane in regards to reflectivity.
How Roof Ventilation Can Help Solar Gain
Proper ventilation can be a significant help, but the root cause of intense solar gain is the level of reflectivity (or lack of reflectivity) of the roof. When a roof is coated with a high reflectivity coating or has a modern single ply roof membrane such as TPO or other similar types of materials installed, the amount of solar energy reflected back to the atmosphere and outer space can be significant. As a side note, high reflectivity roofs are very beneficial to the environment. Global warming is a major ecological concern for the future of our survival on Earth. As modern humans, living in a time at the precipice of pending and concurred ecological dusaster we take energy efficiency and environmental impacts increasingly more seriously. The issue is very political but its becoming increasingly more difficult for leaders (especially with ties to financial interest in policies to exploit the environment) to continue denying science is real. Similar to a green roof, a high reflectivity roof is also much better for the environment, compared to traditional low reflectivity roof systems.
What Is Modified Bitumen Roof System?
Modified bitumen roof systems are modern single-ply roof membranes; However, unlike even better and more efficient roof membranes like TPO systems, modified bitumen roof membranes have relatively poor reflectivity and if smooth modified bitumen membranes are left uncoated, the energy impact to the building can be terrible. There are several types of modified bitumen roof systems, but one of the most common is modified bitumen smooth systems, either APP or SBS.
The image below shows an example of two different side-by-side torch down modified bitumen flat roof membranes.
The membrane on the right is painted a pure white color. This coating was applied about 3.5 years ago. Over that time, the roof has gotten dirty from regular typical debris and dust, but underneath of a layer of dust, the roof is still a bright white color.
Maintaining High Reflectivity Roof
Many people may not realize that a high reflectivity roof must be kept clean to maintain its ultra high, full level of reflectivity. Even when dirty, the flat roof membrane can still be effective to reflect the majority of energy from the sun, but it still loses some reflectivity when the roof is dirty. The difference in solar temperature gain between the black roof on the left and the white roof on the right in the picture above is drastic. The white roof stays relatively cool while the black roof cooks like a skillet in the summer. The Washington, DC geographic areas can have scorching hot days in the summer with intense sunlight.
Front Porch Roof
The picture below shows an example of a front porch roof, typical of many Washington, DC rowhomes. This roof structure is covered with a modified bitumen membrane. This rooftop’s modified bitumen membrane is also uncoated and unprotected. Although this particular rooftop does not cover and interior space, the coating would also help extend the life of the membrane as the coating would help resist the harmful effects of ultraviolet rays.
EPDM roofs are also ofren a black color, and unlike modified bitumen membranes, EPDM membranes are not intended to be coated, in almost all cases. As is, as made straight from the factory, TPO roofs can have manufactured stated levels of reflectivity near 90%. That difference can translate to a major energy savings in the summer and unlike the modified bitumen counterpart which requires a coating, TPO is a low maintenance system and requires no residual coating application.
Maintaining Low Slope Roof Systems
Smart proactive replacement, construction, upkeep and maintenance of low slope roof systems requires an enthusiastic interest and understanding of waterproofing principles and building science. Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building.
We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company. You can learn a lot more on our blog. Feel free to check it out. If you have questions about the roof and related systems of your building in Washington DC, fill out the webform below and drop us a line. We will be in touch if we can help.