The Great White Roof Debate

To limit the creation of urban heat islands, white roofs have become increasingly popular and are the subject of much media attention. Praised by some and questioned by others, there is much debate about the real benefits of white roofs. Here is a summary of the information reported by the two main parties involved.

White Roofs

White roofs according to Association des maîtres couvreurs du Québec (AMCQ)

According to the AMCQ, white roofs are not linked to the decreasing presence of heat islands. In fact, they appear to have the unfortunate consequence of increasing heating costs. The rationale behind this statement is that in a cold climate, such as the one experienced in Quebec, a white roof forces you to start heating much earlier in the fall and for an extended period of time in the spring.

While for some, the motive behind a white roof is to benefit from high energy efficiency, this can also be a letdown. The AMCQ argues that prioritizing good attic insulation is a far better idea, as 30% of the heat is lost through the attic.

Additional drawbacks include the possibility of a white roof soiling over time, to the point of turning gray. As a result, it would lose 30 to 60% of its solar reflectance index. According to an article published on the CORPIQ website, Michel Paré, director of development at AMCQ, stated: "We're talking about a maximum five-year capacity to absorb the sun's rays. After that, we observe the same reflective results as with a grey roof (...)”.

Hence, the questionability of a white roof’s potential to limit heat accumulation. Following this statement, the AMCQ also tried to mitigate the adverse perception of asphalt roofs coated with gravel in relation to the formation of heat islands. As a matter of fact, their heat mass has been proven not sufficient enough to generate heat for more than an hour after sunset.

Photo: Flickr Walmart

Can White Roofs Not Be Cleaned?

Naturally, the next logical thought process is to think about cleaning the roof covering. However, the problem with this is that it can be a risky venture with most of the materials typically used in white roofs. After all, elastomeric membranes degrade over time, and their coating will be affected when cleaned. Furthermore, pure white membranes are solely obtained at an extra cost.

Although white PVC or thermoplastic membranes are easier to clean, they will nonetheless lose their colour with time. Note that cleaning these materials will require professional expertise and represent an additional expense. And, the costs can be considerable as well as the fact that the overall practice can have a negative impact on the environment.

EcoHome: Insight Regarding White Roofs

However, EcoHome supports AMCQ's position regarding heating costs being higher during the fall but still recognizes that white roofs allow for a more comfortable temperature to be maintained in the summer as well as reduce air conditioning costs.

The association also states that membranes used to manufacture white roofs are much thinner than asphalt roofs, which minimizes their environmental impact.

Emmanuel Cosgrove, director of the association, concurs with the AMCQ on the consequences of white roof coverings soiling easily. He also maintains that white membranes will soil within two years to the point that their solar reflectance will be greatly affected.  

Despite the conflicting concerns outlined in this article, if you are interested in having a white roof installed, do not hesitate to contact a contractor who specializes in roofing membranes. They will have the expertise and knowledge to provide you with alternative perspectives on the matter. 

Are you looking for more information about roofing? Check out our Roof Renovation Guide. 

Cover photo: Flickr