If you have ever walked across a blacktop parking lot on a hot summer day, it feels like the temperature just shot up another 20° or more. The surface material has a lot to do with it. When you move off the blacktop and onto some grass, you can feel the difference.
The same thing applies to your roof. A dark roof will absorb the light and turn it into heat, which could transfer into your home and discharge it back into the atmosphere. A light-colored roof will reflect the light without turning it into heat. A green or vegetative roof will absorb the sunlight and employ it to the best advantage.
How Hot Does Your Roof Get?
On a full-sun, 90°F summer day, here are the temperatures you can expect your roof to reach:
|Black roof||140° to 190°|
|Aluminum reflective coated||Up to 68° cooler than a black roof|
|Gravel||125° to 140°|
|Unpainted metal||138° to 145°, but feels hotter to the touch|
|Painted metal||105° to 115°, or 42% cooler than unpainted metal|
|White||102° to 120°|
|Vegetative (Green roof)||90°|
It’s important to note that there are two factors involved in the temperature of your roof:
- Solar reflectance, or the ability of the material to reflect energy into the atmosphere
- Thermal emittance, or the amount the material rejects instead of absorbing
These factors are measured on a scale of 0 to 1, with a higher score indicating a cooler roof.
What are the differences between the various roofing materials?
If you have a black roof, the temperature of your roof is going to be the hottest. Though designed to last 20+ years, heat can decrease life expectancy because it breaks down the materials quickly. In fact, from a longevity standpoint, wear and tear from heat is the major problem.
A metal roof can also get hot, so it’s a good idea to go with painted metal instead of unpainted. While you can use unpainted metal and have it painted after installation, it’s best if you go with pre-painted metal.
If you have a white roof, the temperature of your roof can be 50°+ cooler than a black roof and nearly 30° cooler than a gravel roof.
If you choose a coated roof, whether elastomeric or aluminum, the temperature of your roof will be cooler than a black roof, and technology makes it possible for you to choose the color you like, still substantially reducing the temperature of your roof.
Finally, if you have a vegetative roof, the temperature of your roof will be the same as the surrounding atmospheric temperature. After all, nothing can keep your roof at a pleasant temperature than a living, breathing, cooling material.
Why are vegetative roofs cool?
On most days, regardless of the atmospheric temperature, the temperature of a vegetative roof is cool to the touch. It is in total shade, a traditional roof protected under a canopy of vegetation. The cooling qualities are much more than the individual rooftop because a vegetative roof does not reflect the heat into the atmosphere, reducing the heat island effect on the city.
How does a hot roof affect the temperature inside your building?
When your roof is hot, does it affect the temperature of your building? Yes, it does. The roof absorbs heat, and some of it transfers into the building- especially if you have an older building that was not built with R20 and R30 insulation. The newer insulation did even better than the insulation available just a few years ago. Also, adding a white or silver coating will reduce the heat radiation of your roof enough that you can scale down your AC requirements. This will reduce your energy consumption and the demands on the power grid that affect pricing.
According to the Green Building Alliance, a cool roof can translate into a 7% to 15% reduction in your overall cooling costs. Of course, it is important to note that to get the best benefits from a painted/coated roof, it needs to be kept clean and repainted every 10 to 15 years.
Should You Change Your Roof?
Believe it or not, the temperature of your roof in summer is something you can control and should be considered during a re-roofing or new construction project. You may be able to do some things to cool down your current roof. Contact the professionals at A&J Reliable to learn more about your roofing options. We offer free roof inspections, and estimates on the work we determine should be done for your roof. Please contact us today if you are in New York, New Jersey, or the surrounding area; we would love to help you keep your roof cool in summer.