Have you noticed how much cooler you feel when you wear light colored clothes on a hot day? The reason is the color of the clothes which cause it to reflect the sunlight instead of absorbing it. Roofs are like that too and operating on the same principle, cool roofs make use of solar-reflexive surfaces to in order to maintain lower roof temperatures. The temperatures attained by a traditional roof may reach 150oF (66oC) during a hot summer day while it may not exceed 50oF (28oC) under the same conditions.
How Cool Roofs Function
Cool roof have higher Solar Reflectance (SR) and Thermal Emittance (TE) values than the traditional roofs also known as dark or hot roofs. SR and TE are the core material surface properties used in determining the temperature of a roof and a larger value reading of these properties on a scale of 0 to 1 is representative of a cooler temperature under the sun.
Dark roofs typically absorb over 90% of the incoming solar energy thus raising the temperature of the roof to over 150oF (66oC) on a sunny day. This generally results in more heat entering the house. The solar energy absorbed by cool roofs however, is less than 50% thus keeping the internal temperature within the house low.
Cool roof surfaces therefore possess higher efficiency in reflecting sunlight and emitting heat than the traditional roofs. The result is that they are able to keep cooler in the sun.
Qualification as a Cool Roof
One of the metrics for determining whether a roof qualifies as a cool roof is its measurement on the Solar Reflectance Index (SRI). The SRI is represented by a value derived from calculation from the Solar Reflectance and Thermal Emittance values. The higher it is, the cooler the roof will be in sunny conditions. A roof would therefore qualify as a cool roof if it meets or surpasses the minimum SRI requirement. For example, the minimum SRI requirement as cool roofs by the California Energy Commission is 64 and 16 for low and steeped sloped roof types respectively.
Do You Need a Cool Roof?
Obviously, give its enormous benefits, a cool roof would seem like a necessity for every commercial property owner but then there are some considerations to bear in mind before taking the plunge.
You would need to find out the type of roof required or most appropriate for your building in order to determine if there is a fitness for purpose. In some regions, cool roofs are actually a requirement for certain building types. Will the cool roof add to your costs and by how much especially when weighed against long-term savings? Tax rebates or other incentives could also be available. Availability is also an important factor as well as durability.
It is quite obvious that cool roofs are important for most commercial roofing projects but the considerations that have been raised need professional and expert consultation. Gillespie Roofing has wide industry experience and has successfully consulted for many clients on a diverse range of commercial roofing projects.