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Part 2 – The Basics of Energy-Efficient Roofing


Cool roofs are the biggest buzzword in roof energy efficiency today. They work by reflecting a large fraction of incident solar radiation, dramatically reducing the amount of heat absorbed by your home. They also quickly release whatever amount of heat they end up absorbing.

But is reflectivity and emissivity all there is to an energy-efficient roof?

The short answer is NO. According to former California Energy Commissioner Art Rosenfeld, the ideal energy-efficient roof is:

  1. 100% reflective in summer; and
  2. 100% absorbent in winter.

The thing is, such a material doesn’t exist (yet). Modern cool roof materials are around 65% reflective (meaning they absorb around 35% of the sun’s energy). And unfortunately, the emissive and reflective properties of roofs don’t really change to suit the changing seasons. The ideal 100% reflective/100% absorbent roof is—for now—an impossibility.

But Rosenfeld’s definition of an ideal roof emphasizes an interesting point: focusing on a roof’s ability to absorb heat can also make it more energy efficient.

About Thermal Mass

Thermal mass refers to a material’s ability to absorb and store heat (the term is also used to refer to the material itself). A material with high thermal mass can hold a larger amount of heat and takes longer to fully absorb and release that heat compared to a material with low thermal mass.

You can think of a thermal mass as a high-capacity “battery” that gets charged and then releases, not electrical energy, but heat.

Roofing materials with high thermal mass can reduce the heating and cooling needs of homes in most climates. They are flexible enough to have the ability to:

  1. keep a home cool when it is hot out (by slowing down daytime heat transfer from the exterior to the interior); and
  2. keep a home warm when it is cold out (by slowing down heat loss from the interior to the exterior).

Roofing Materials with High Thermal Mass

Two things make a material a good thermal mass: a high specific heat capacity and a high density.

Roofing materials that meet these requirements include clay tile, concrete tile and slate. (Bonus: clay and concrete tile roofs can be modified with reflective coatings to make them even more energy efficient.)

A Quick Note

Roofing materials with high thermal mass tend to be heavy, so your roof deck and the underlying structures must be able to handle the weight. If you’re switching from a lighter material, modifications will have to be made to ensure that the structural integrity of your home won’t be compromised.

What if a roof replacement isn’t in the offing? Find out how you can harness the cool benefits of cool roofs without a complete reroof in Part Three of this series.

The Roofing Company 7-Point Satisfaction Guarantee

Learn what your Neighborhood Roofing Professional promises you...

The Roofing Company 7-Point Satisfaction Guarantee

Learn what your Neighborhood Roofing Professional promises you...


Frequently Asked Questions About TPO Roofing

Frequently Asked Questions About TPO Roofing

As fall starts, many homeowners are calling roofers in Chesapeake for roof inspection, repair, or replacement.

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