A Complete Guide to Cool Roofs and Roofing Materials
A cool roof is essential when living in warm climates like in Phoenix, Arizona; but the benefits of a cool roof are valuable for any homeowner.
Recently, I read a report about one such roofing material: something capable of keeping the roof – and interior of the building – much cooler than the hot air outside and the surface temperature of the roof exterior.
Roofs heat up VERY quickly under the Arizona sun. When it’s 100°F out – not unusual in Arizona –the surface temperature of a traditional asphalt roof can easily be 140°F – even 160°F. Even a roof made from reflective white material can still be hotter than the surrounding air temperature by 10-15°F.
This is a problem because the temperature of the roof still greatly affects the internal temperature of the home. Much of that heat is still absorbed through the roof, into attic, and then into the home blow.
The hotter your roof is, the more difficult it is to stay cool inside – and harder your AC unit must work to keep your home at a comfortable temperature.
New Roofing Material Can Keep Your AZ Home Cooler
Cool roofing is not an entirely new concept. Researchers have been studying materials that can reduce solar reflectance and thermal emittance for decades, if only so that energy consumption due to cooling buildings could be reduced. The first “cool roof” material was introduced in California in 2001.
But over the past few years, the number of cool roofing materials and options has exploded – and new ones are being created all the time.
A new roofing material – the one I read about – was found by scientists in Australia just a few years ago that boasted of some very impressive numbers.
This “coated polymer stack,” as they called it, boasted of keeping roofs up to 11°F cooler than even the best white roofs already out there – potentially reducing the urban heat island dramatically. It’s reported that if a number of commercial buildings in an area are all coated in this new material, that the heat that radiating from the buildings would be reduced by several degrees.
That could potentially reduce the urban heat island dramatically – and be a serious game changer.
Best Cool Roofing Materials for Phoenix Homes
Until ground-breaking technology like that is in production and widely available, we’ll have to “settle” for some of the cool roofing materials already on the market. Thankfully, these materials are very effective and anything but “conventional.”
Here are the cool roofing materials already busy keeping houses cool all across Arizona, and some of the benefits and drawbacks of using each.
Asphalt shingles are traditional roofing materials, but usually aren’t the first thing on people’s mind when they think “cool roofing material.” That’s because the thermal emittance of asphalt is still rather low – even white asphalt, which is only about 30% reflective. Asphalt is a great low-cost roofing material, but there are better choices for keeping your home really cool.
Metal Cool Roofing
Cool metal roofing is a popular cool roofing material, as it can offer more than twice the solar reflectance of traditional asphalt roofing: up to 70% when paired with a colored reflective coating.
Compared to the 30% solar reflectance of asphalt shingles, that’s a dramatic difference.
By some accounts, you can save more than 20% of your cooling bill in the summer simply by switching to cool metal roofing.
Additionally, metal roofing is quite durable – the most durable of all roofing materials. Made from aluminum or zinc-coated steel, It’s surprisingly lightweight and sturdy, as well as weather-resistant and good at resisting mold and mildew growth. A good metal roof will last anywhere from 30 to 50 years with the right maintenance. It is usually more expensive than other cool roofing materials, but the investment can pay itself off many times over. It’s also fully recyclable.
Reflective Roof Coatings
White Roof Coatings:
White reflective coatings are some of the most effective cool roofing materials out there. Have you ever noticed how MANY cars in Arizona (and other HOT locales) are white?
It’s because white is extremely reflective. That’s also why people tend to wear white clothing on hot sunny days – to keep themselves cool.
White coatings are opaque, usually made from a polymer or similar material, mixed with some kind of white pigment or paint. And they’re VERY effective: a good white-coated roof can reflect up to 80% of solar energy that hits it. That’s even more than metal roofing – and can make a huge difference in your home’s interior temperature. The surface temperature of a white roof can be virtually the same as the ambient air temperature around it.
Pigmented Roof Coatings:
Pigmented roof coatings come in different colors – besides white – but aren’t quite as reflective or effective as white cool roof coatings. If you have a dark color like green, black or red, that might only reflect about 20-30% of the solar radiation from the sun – for the same reason a dark-colored car will be hotter than a white one in summer. Lighter colors, however, such as raw cotton (a light yellow) can be extremely reflective – up to 80%.
Pigmented roof coatings are popular for residential homes where appearances matter but aren’t a great choice for cool roofs. But as dark colors are just not very effective at reflective sunlight, and lighter color ones are better. And, like white coatings, the thicker the coats, the more reflective the roof.
Aluminum Roof Coatings
While white and pigmented roof coatings are usually made from some polymer material, aluminum roof coatings use a resin (similar to asphalt) that contains aluminum flakes. The flakes create a “leafed” effect that covers most of the roofing, creating an almost solid top layer to reflect solar energy.
Aluminum roof coatings can reflect as little as 50%, or more than 70% with some premium, high-end models. Used properly, they can easily cool the interior temperature of the house by 10+ degrees – a HUGE difference.
Unfortunately, aluminum also absorbs and radiates heat that isn’t reflected, becoming hotter than a composite material with the same “flaked” coating otherwise would.
Roofing membranes are composite materials made from flexible, sturdy, usually waterproof materials: usually a combination of felt, fiberglass, or polyester with a polymer, asphalt or synthetic rubber to connect them and attach them. A reflective coating or pigment is often applied to the top, to maximize reflectivity.
Common roofing membranes include single-ply EDPM or PVC, the reflectivity of which depends on the pigment used; a white EDPM or PVC roof can repel roughly 70% of solar energy, while a black one will reflect almost none. Some premium cool roofing manufacturers, like Ecology or Sika-Trocal, make membrane roofing that repels 80% + of solar energy.
Other benefits of membrane roofing include flexibility and durability, ease of installation and maintenance, and low cost – all reasons why they’re the most common type of commercial roofing.
Tiles are another excellent, but often overlooked, cool roofing material. They’re most popular in warm, sunny climates, where they tend to match the earthen look of the homes – like here, in Arizona. Usually, they are made from ceramic, but can be made from cement as well. Clay is more reflective than cement, but tile’s reflectance depends heavily on their color, as well: red clay might only reflect 20%, but a white clay tile can reflect up to 70% of solar energy.
Other reasons to get clay tiles are durability and recyclability; quality ones made of natural materials can be 100% recycled when you’re done with them (although that may not be for a long time; a real clay roof can last 50 to 100 years).
Just think of how much energy this sharp-looking roof material could save you (and your descendants) over an entire century…
They’re also totally non-combustible, making them an excellent choice where safety is paramount.
Drawbacks to tile roofs include cost and weight. Clay and cement weigh a lot more than either asphalt shingles or most metal roofing and is a lot more time-consuming (and thus expensive) to install.
But when you have the money – and the tile look fits your home perfectly – then you can count on tile to keep your home cool (and your AC bill low).
For more information on cool roof standards and their evolution, click here to download a complete guide.
Estrella Roofing Installs the Latest in Cool Roofing
I will eagerly await the manufacturing of this new material. Until then, here are some suppliers of cool roofing materials that we use here at Estrella Roofing: