White roofs are one of the latest trends in energy efficiency. They are installed in residential, commercial, industrial, and institutional buildings, in both the United States and Canada. Over the past 15 years, white or reflective roofs have become very popular. They are even required by regulations in some northern cities, such as Montreal.

It is true that in some warmer climates, white roofs are a useful and effective option. However, their systematic use in cities north of the 45th parallel raises serious questions and, in my opinion, requires careful consideration of each project before perpetuating the trend of reflective roofs.

The Myth of White Roofs

Popular popularity, as well as many regulations that are not scientifically based, tell us that white roofs always save energy and reduce pollution. Unfortunately, this claim is a myth!

The purported advantages of reflective roofs, especially in colder climates, are based on flawed science and self-serving marketing that has led to the belief that white roofs are energy-efficient and more cost-effective than conventional roofs.

What is the reality?

In fact, white roof membranes have high reflectivity, which directs heat upwards, much like high-performance glass. Consequently, the presence of a vapor barrier on the warm side of an assembly, which is required by the Building Code, traps an abnormal rate of condensation beneath the white membrane, which itself has low water vapor permeance.

The result: extreme condensation problems, water infiltration, degradation of ventilated wood decking, and much more! And who will be held responsible for these problems? Given that the contractor installs white membranes out of obligation in areas designated by the municipal authority and current regulations, without being able to consider the building’s construction type and its surroundings, can they be held responsible for the resulting problems?

Reducing the urban heat island effect: two-way consequences

In the urgent need to reduce the “urban heat island effect” by a few degrees in summer, white roofs have been presented as a life-saving solution to combat climate change. In northern countries like Canada, this notion remains true for only a few weeks a year, six weeks at most!

This same phenomenon is significantly reversed in winter, when the accumulated snow on the surface acts as additional insulation. Not to mention the accumulated dirt, which considerably reduces the reflectivity, starting as early as the second year after installation.

What the Studies Say

All the studies conducted, including the one from Lawrence Berkeley National Laboratory, demonstrate the effectiveness of using white reflective roofing everywhere, including in northern climates. However, these studies do not take into account thermal performance, air infiltration, or vapor entrainment. They are limited to measuring the surface temperature at the roof level.

Newer studies, including one from Virginia Tech, call into question the energy savings of white reflective membranes and challenge the assumption on which standards and codes were based. They demonstrate that the reflectivity of windows, masonry walls, ventilated roofs, and many other factors contributes more to the increase in ambient temperature and can even negate or cause problems such as condensation.

https://news.vt.edu/articles/2017/10/CAUS-Black-White-Roofing.html

Architects, engineers, building owners, and roofing system designers also question their scientific validity. In a PDF document available on their website, RCI acknowledges that for colder climates, installing a reflective roof is not always the ideal option.

https://iibec.org/wp-content/uploads/PS-2018-17-Cool-Roofing.pdf

Thermal image showing condensation contamination of a wood roof deck after only two years of installation.

My expertise, my question

Working as a building envelope waterproofing consultant specializing in infrared thermography and having no affiliation with any membrane manufacturer, I believe I have an impartial perspective and expertise supported by some very unfortunate realities.

Considering the various problems associated with white roofs in northern climates, a question arises: must we wait for major roof collapses before reconsidering the systematic installation of white roofs on buildings?

______________________

Source:

• Article published in the Baltimore Sun on October 28, 2013, written by Mr. Samir Ibrahim, Director of Design Services and Project Reviews for Carlisle SynTec Systems
• Cool vs. Non-Reflective Roofing, RCI. (http://rci-online.org/wp-content/uploads/PS-2018-17-Cool-Roofing.pdf)

Michel Desgranges, T.Sc.A.
#OTPQ : 18788