By Brady Kolden, National Coatings Business Development Manager
Contrary to popular belief, the surface temperature of a roof is not determined by air temperature alone. The position of the sun, UV levels, time of day, air quality and circulation, and type of roofing materials all impact the heat buildup on a roof. A 90°F afternoon with the sun directly overhead will produce far hotter roof surfaces than the same temperature in the early evening when the sun sits lower in the sky.
To understand how different types of roofing materials handle heat, our building envelope specialists at Polyglass recently decided to measure temperatures across different roof sections using thermal imaging over three hottest months of the year.
The Effects of Ambient Temperatures on the Roof’s Thermal Performance
We installed a polyurethane foam roofing system on top of an existing Built-Up Roof (BUR) with a gravel surface at a site in Henryetta, Oklahoma. The city is known for extremely hot and humid summers, with high temperatures around 87°F (31°C), with lows around 69°F (20.8°C). July sees the peak warmth, with afternoons reaching 92°F (33.3°C) and evenings dropping to 72°F (22.4°C). August hovers around 92°F (33.3°C) during the day and cools to 71°F (21.7°C) at night.
Now, we know that the hotter a roof gets, the harder a building’s air conditioning has to work to cool things down, which drives up energy costs.
Our goal was to find out how the most commonly used roof substrates heat up to different degrees based on the time of day, sun angle, and atmospheric conditions (haze, humidity, etc.). The heat of June, July, and August allowed us to test spray polyurethane foam, EPDM rubber (Ethylene Propylene Diene Monomer), TPO (Thermoplastic Polyolefin), gravel BUR (Built-Up Roof), asphalt shingles and wood shingles under the most challenging conditions.
After mechanically scraping off gravel carefully, we applied the water-based PolyBrite 780 primer to bond the new roofing system firmly to the clean prepared surface. Next, a layer of spray-applied polyurethane foam (SPF) was installed at a thickness of 1.5 inches. The foam used had a density of 2.5 pounds per cubic foot, which indicates it was a high-density material to provide exceptional insulation and long-term resilience. On top of the foam, a protective coating of PolyBrite 90 Series High Solids Silicone was put on in a layer measuring 35 dry mils thick (35 mils equals 35/1000 of an inch). The silicone is vital because it protects the foam from UV radiation, moisture, and weather damage, and keeps it watertight and energy-efficient.
Finally, roofing granules were spread over the silicone while it was still tacky. The granules embedded nicely into the surface as the silicone dried and provided a weather-resistant roofing system that outperforms the existing BUR structure.
What We Found
In the measurements taken over three months (on three different days), our roofing engineers noted that the coated SPF foam stayed significantly cooler than the other components, making it 39°F cooler than Gravel BUR and 43.5°F cooler than EPDM. On June 19, 2024 (2:00 pm), when the outside temperature was observed to be 90°F, SPF foam plated with PolyBrite 90 system remained between 88°F and 93°F, averaging 90.5°F.
Uncoated SPF was much hotter at 100°F, and gravel BUR heated up to 129.5°F. EPDM rubber and Capsheet BUR reached 134°F. TPO was in the 106°F to 111°F range and metal roofing was between 110°F and 135°F. The liquid applied PolyBrite 90 worked extremely well in preventing the roof from absorbing too much of the sun’s energy.
Next month, on July 15, 2024 (5:30 pm), when the ambient temperature was 99°F, silicone-protected foam roof averaged 96.5°F, while EPDM was around 122°F, Capsheet BUR was 125.5°F, and metal stayed at 110°F. Although TPO was found to be cooler than before at 103°F. Even though it was boiling outside, the foam-covered roof only rose a little. The PolyBrite 90 system and newly-installed polyurethane foam was 18.6 degrees cooler than other sections of the roof (EPDM, TPO).
The roof showed a consistent performance on August 21, 2024 afternoon as well. The new polyurethane foam system with Polybrite 90 kept the roof 26°F cooler than the other roofing systems on the building. On average, the foam-coated roof was much less affected by heat compared to the other materials. TPO performs better than EPDM but still gets hotter than the foam-coated roof. You could say it’s a decent middle-ground option.
Cut Down Your Building Cooling Costs with PolyBrite Reflective Roofing Systems
When the temperatures of the other parts of the roof were measured, they were, on average, 21.5% hotter than the foam-coated section. No matter what time of day it was, the foam and silicone system outperformed all the other alternatives. But when the sun is directly overhead and the temperatures are at their highest, that’s when you see the resilience of PUF foam system. At the height of the afternoon sun, the foam and Polybrite 90 together kept the roof over 20% cooler than the other systems. The cooling effect not only reduced the heat on the roof itself but also helped to lower the temperature inside the building.
A cooler roof deck and surface not only keeps the heat out, it helps your building save money year-round by reducing the amount of heat that gets trapped inside. Your air conditioning doesn’t have to work overtime to cool the building down. The result is considerably lower energy bills. Think about it: if your HVAC system has to run less, yes, it consumes less power, but there is also less wear and tear on the system. A thermally efficient roof extends the life of your HVAC equipment and minimizes the need for roof repairs or complete roof replacement.
With the addition of PolyBrite 90 to your PUF roofing system, you can slash your roof temperature by over 20%, keeping it cool when the sun is at its hottest. You’ll be saving thousands of dollars every year, and if you have a large industrial or commercial property, those savings will add up even quicker.
When your roof is hot, the entire building gets hotter. Like a sponge, the roof soaks up the sun all day long and that heat seeps through. The stifling indoor air makes for a very uncomfortable environment for your customers, tenants, and employees. With PolyBrite 90 silicone, that heat starts bouncing right off instead of absorbing into the structure and eliminates the possibility of high indoor humidity (and thus, mold). Whether you are at home, in the office, or working out in a gym, it’s easier to focus and be productive when the air around you is clean and fresh.
To learn more about PolyBrite roofing solutions and how this upgrade can deliver immediate, tangible results for your flat roofs or low-slope roofing project, get in touch with us.