You know how walking across a blacktop parking lot on a sunny day can feel like the temperature just went up 20 degrees? It’s not your imagination – surface material has a lot to do with temperature. Move from the blacktop to the grass and you can instantly feel the difference.
It’s exactly the same with roofs. Dark roofs absorb light — up to 90% of solar energy — and convert it to heat, emitting it back into the atmosphere. White ones absorb much less light by reflecting the light without transferring it into heat.
Here’s the kind of temperatures you can expect your roof to reach this summer depending on its surface:
|ROOF SURFACE||DEGREES FAHRENHEIT ON A SUNNY, 90-DEGREE DAY|
|Aluminum reflective coated||Up to 68 degrees cooler than black roofs|
|Unpainted metal||138-145, but feels hotter to the touch than a black roof|
|Painted Metal (ex: BASF Cool Paint)||105-115 or up to 42% cooler than unpainted metal|
Effects on the temperature inside your building
Does a hotter roof make for a hotter interior? Absolutely. Heat can be absorbed by your roof surface and radiated inside, especially in buildings with older roofs that were not assembled using R20 and R30 insulation. Newer insulations do a better job than even just a few years ago. And if you also add a nice white or silver coating, you can reduce heat radiation enough to size your AC requirements differently. Which in turn reduces your energy costs and the demands on the power grid that contribute to energy pricing from the utility company.
Should you change your roof to keep it cooler?
How hot your roof really gets in the summer is a variable you have some control over. It’s definitely something to consider when re-roofing and in a new construction project, and you might be able to take steps to cool things down on the roof you already have. Plus, new coating technologies are being developed all the time. A recent study in Australia showed promising results from coatings that can keep the roof even cooler than the surrounding air.
Our team at LaFerney can advise you on your best options for your particular roof that will also align with your long-range goals for your building.
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