The Pros and Cons of Cool Roofs
If you start investigating eco-friendly materials for your roof, sooner or later you’re bound to come across the idea of a “cool roof”—a surface that’s specially designed to reflect heat, rather than absorb it. When you really stop and think about it, it makes total sense. After all, you wouldn’t throw on a black sweater and jeans to go out on a steamy summer day, would you? So why should your roof be clad in heat-absorbing dark colored shingles? Especially since that heat gain can transfer into the rest of your home, driving up cooling costs?
Well, that’s exactly what air conditioning experts and building-energy-use researchers were wondering when they first designed cool roofs. Their studies showed that light-colored, reflective materials reduced the need for air conditioning in building interiors, particularly during the hottest part of the day when cooling demand was highest. And without a bunch of heat-soaked surfaces dotting metropolitan areas, cool roofs might help reduce the urban heat island effect—the climatological buildup of heat and greenhouses gases in densely populated areas.
Unfortunately, cool roofs may not be all that they’re cracked up to be. Most notably, a prominent Stanford study revisited the effects of light-colored roof surfaces and found that they might actually speed up global warming, rather than working to reduce it. So is this controversial roof surface right for you? What are the pros and the cons? Read on for the full scoop.
What Exactly Is a Cool Roof?
No, it’s not a roof that wears shades. Typically composed of a heat-reflective material—like treated asphalt shingles, tiles, or just a roof surface painted with a special, reflective pigment—cool roofs can be installed during a roofing replacement project or by retrofitting existing shingles using a cool roof coating. In fact, many homeowners choose to add specialty coatings to their roof surfaces. These silicone, acrylic, or polymer paints typically contain UV resistant materials and can be applied to roof surfaces after the fact.
Cool Roofs Cut Cooling Costs in Hot Climates
Even opponents have to acknowledge that cool roofs cut air conditioning loads. According to the Department of Energy, roofs can easily reach up to 150 degrees Fahrenheit on the hottest days, whereas installing a cool roof reduces those surface temperatures by as much as 50 degrees. And when energy experts evaluated cool roofs in California, Florida, and Texas, they found that their installation reduced electricity demand during peak power times by 10 to 30 percent.
Cool roofs obviously work best for hot climates, where the cooling season is longer and air conditioning is in high demand. In fact, in colder areas, they may have the opposite effect, driving up heating costs in the winter.
But They Could Increase Global Warming
But the problem with cool roofs, as with many green products, is that the environmental impact as a whole needs to be weighed when evaluating their actual benefits. The newest research looked at the net global warming for light-colored surfaces, rather than its effect on a single building or small area. This analysis found that white roofs actually contribute to global warming rather than reducing it.
That’s because these surfaces set off a chain reaction that increases the amount of sun cities receive. The white surfaces reduce the vertical transport of moisture to the atmosphere, which in turn limits cloud coverage. That means less rain and an increase in drought conditions—the opposite of the intended effect. The finding highlights a flaw at the root of the cool roof philosophy—namely, that more research needs to be done before these surfaces can be declared energy efficient.
Sealing Your Attic: The Safest Way to Reduce Cooling Loads
Experts may not agree on the benefits of cool roofs. But most will tell you that you can reduce cooling costs by properly sealing off your attic from the rest of your home. That way, your air conditioning won’t leak from the interiors below. Floors should be properly insulated with insulation blankets and vapor barriers, if necessary. Gaps around soffits, utility chases, and recessed lights should be patched with drywall and sealed with expanding foam or silicone caulk. Additionally, you can add weatherstripping around your attic access door to create a super-sealed energy-saving effect. Now that’s a cool idea!
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