Cool Roofing Crosses Into Uncharted Temperatures

Extreme heat is pushing some roof materials to the edge of failure, but reflective roofs offer a welcome bridge between breakdown and durability.

Image: CertainTeed Solaris Reflective Roofing

I’m currently contracting out the re-roof of a Florida house with one of CertainTeed’s reflective shingle lines, Solaris.

Apparently, these shingles are installed less commonly than you might think. The roofer had to special order my batch from the plant in North Carolina, causing a three-week delay.

Why, I wondered, are cool roofs not dominating the market here? Simple: they cost more. Or do they? That depends on whether you include lifespan and HVAC savings in the bottom line. Most homebuyers don’t look much deeper than color and warranty on a new roof. My roofer says few of his clients will pay for a cool roof upgrade (about $5,000 extra on a 2,000 sq. ft. home).

Maybe that would change if builders and homeowners knew the whole story. Not only might a “cool” roof pay for itself simply by lasting longer than standard shingles, it could also protect the other vulnerable parts of the roof assembly from costly replacement. New levels of summer heat make the case for cool shingles much more compelling.

The Science of Roofing Heat Stress

Let’s narrow our focus to asphalt-modified shingles, felt underlayments, and osb roof decks, because their performance under heat stress is well documented.

Standard asphalt-based shingles (including fiberglass/asphalt composition) usually have service temperature tolerances up to around 180–200°F (82–93°C). At those levels, they may begin to soften, lose granules and age rapidly. In part, this is because sustained high surface temps increase oil exudation (where asphaltic oils seep to the surface), leading to premature brittleness and cracking.

Past studies  have measured peak roof temperatures for asphalt shingles in hot climates at about 170°F (76°C)—just brushing the edge of the “breakdown” zone. The rest of the roof, including OSB decking and traditional felt paper underlayment, has about the same tolerance for sustained heat before they too start to show negative effects.

These roof temperature estimates, however, are based on yesterday’s weather data: when hot days rarely exceeded the 90-to-100-degree range. The world is getting hotter, and that’s a problem for both new and existing roofs.

Oak Ridge National Laboratory (ORNL) Estimates that dark asphalt shingle roofs can run 50–70°F (28–39°C) hotter than the ambient air temperature under typical summer conditions. So if the ambient temperature is 90°F (32°C), shingles on a roof surface might reach 140–160°F (60–71°C). If temps hover around 120°F for several days, as they did in some places last year, shingles may hit 190°F or more, suffering permanent damage.

Hot Cities in 2023—New Extremes

The worst sustained heat has been happening in the West, but Southeast States also are feeling the trend, and scientists are unsure how much higher the new normal temperatures might get.

Preventing Damage and Extending Roof Longevity

A study by the Lawrence Berkeley National Laboratory found that cool roofs can lower surface temperatures by up to 50°F (28°C) under peak conditions. In the context of rising temperature extremes, they offer roofing assemblies a “safety zone”

First, they prevent shingles from reaching damaging temperatures. By maintaining surface temperatures closer to ambient air levels, they reduce thermal cycling, the repeated expansion and contraction of materials due to temperature changes. This, in turn, minimizes cracking and extends the functional life of shingles by several years.

Next, they protect traditional underlayments and roof decking. The materials beneath shingles, including some underlayments and roof decking, are susceptible to heat-related damage when temperatures hit extremes. For example, the resins in OSB have been found to break down beginning at about 200 °F (93°C). It should be noted that some of the more modern underlayments can handle higher heat, up around 240°F, but felt paper cannot.

And finally, they clear the way for radiant barriers. Without reflective shingles, applying a radiant barrier on the underside of a roof could push roof assemblies into the red zone. By adding cool roofing, this affordable heat defense remains one of the best retrofit approaches to knocking down temperatures in attic spaces.

A simulated study of a residential attic in El Centro, California , by Oak Ridge National Laboratory, for example, found that “installing a radiant barrier in the attic of a home with a cool-colored shingle roof resulted in a 28.2% reduction in energy consumption compared to a conventional roof and attic assembly. This combination was found to be as effective as doubling the ceiling insulation from R-19 to R-38.”

In another analysis, researchers noted that the radiant barrier has the added benefit of compensating for any “heating penalty” a roof might incur by having a cool roof during winter months.  The radiant barrier essentially isolates the roof assembly.

Reducing the Need for Attic Ventilation

Without proper ventilation, attic temperatures can exceed 150°F (65°C) in summer, straining HVAC systems and contributing to heat transfer into living spaces. Cool roofs, by significantly reducing heat absorption, lower attic temperatures and diminish the reliance on mechanical ventilation.

A simulation conducted by the Oak Ridge National Laboratory found that homes with cool roofs had attic temperatures reduced by up to 30°F (17°C) compared to homes with conventional roofs. This reduction not only lowers overall HVAC cooling costs for a ducted system, it can alleviate the need for powered attic ventilators, saving homeowners additional energy costs.

ROI: Selling the Cool Roof Advantage

Given these factors, cool roofing should be an easy upgrade to sell to homebuyers. Key perks include:

Energy Savings. Cool roofs can reduce air conditioning costs by 10-15% annually, depending on the climate. For example, in regions with average summer temperatures of 90°F (32°C) or higher, a typical household can save $200–$300 per year in cooling costs. Over a 20-year roof lifespan, these savings can total $4,000–$6,000.

Extended Roof Lifespan.By preventing heat-related damage, cool roofs can add 5–10 years to the lifespan of a roofing system even in normal conditions. That figure is likely larger in our new, extreme temperature scenario. The average cost to replace a residential roof is about $14,000, with a 20-year warranty. Cool roofs can add about 30% to the lifespan, equivalent to another $6000 In value.

Higher Resale Value. When home sellers put on a new roof, in some markets they recover 100 percent of the cost of installation. There’s no data on exactly how cool roofs impact a home’s price, but  if a contractor helps them understand the value added, the bump in value should be significant.

Incentives and Rebates. Most cool roofs qualify for the ENERGY STAR federal tax credit, up to 30% of installed cost (capped at $600). Also, many municipalities and utilities offer local rebates for installing cool roofs. For example, Los Angeles provides up to $0.20 per square foot for reflective roofing installations. That’s a $400 rebate on a 2,000 sq. ft. roof.

Given the many financial advantages of cool roofing, upgrading to these products should be almost automatic in hotter parts of the U.S. Along with the ROI points I’ve discussed, longer lasting roofs reduce the asphalt waste load. While 10 to 20 percent of post-consumer asphalt shingles are recycled, the industry still has a long way to go before these products can be said to be sustainable. Cool roofing offers a step in the right direction.