What is a Radiant Energy Barrier?

By Vernon Trollinger, March 10, 2017, Energy Efficiency, Green, Home Improvement, Save Money

While most homeowners love their homes, not every home is perfect. There are either one or two things the homeowner would like to change, such as an outdated bathtub for a new walk-in shower or updating the look of their kitchen. And then there’s occasional “uh-oh” of the unexpected repair. In our How to Shop for Home Improvement Projects series, we’re going to identify several projects and some of the ins and outs of what you can expect.

How to Shop for Home Improvement Projects - Radiant Energy Barrier | Bounce Energy Blog

How to Shop for Radiant Energy Barriers

More than one sweaty homeowner has remarked that the Devil spends summer vacation in a Texas attic because it’s the only place that feels like home. With the sun blasting practically straight down on to shingles and decking, it’s little wonder an attic’s temperature can climb past 150°F. As the sun shines, its heat energy is absorbed by the entire structure of your home’s roof. It gets hot and begins to radiate and emit this heat into the attic space, warming everything that’s in there, often as hot as 150°F. Eventually, the home’s framing will conduct this heat down into the living space. Radiant energy barriers, however, prevent (or slow down) this process by reflecting the heat energy back into the roof and ultimately back into space. By keeping the heat out of your attic, your home stays cooler. While radiant heat barriers are good way to deal with that heat, there’s a lot of confusion about what works best.

A Matter of Materials

The two basic types of radiant energy barrier materials are reflective paint and reflective foil. The spray-on paint is known as an interior radiation control coating (IRCCs). It contains aluminum flakes and when applied to the underside of the roof decking, the aluminum flakes reflect the infrared heat back into the roof assembly and outside.

How to Shop for Home Improvement Projects - Radiant Energy Barrier | Bounce Energy Blog

The reflective aluminum foil or a combination of foil and plastic does the same thing as the paint. Installation technique is sometimes hotly contested between attaching the barrier foil face-down directly against the underside (attic-side) of the roof decking versus stapling it across the bottom of the rafters, from the lowest point near the eaves soffits all the way up to the peak near ridge vents. The former is currently the most common.

The difference between paint and foil is cost and performance. In terms of cost, paint prices runs about $50/gallon to cover roughly 375 sq. feet. Double-sided barrier foil to cover the same area costs about $100. In terms of performance, testing shows that foil radiant barriers out perform paint, reducing attic cooling loads by 34% for foil versus 24% for paint.

How to Shop for Home Improvement Projects - Radiant Energy Barrier | Bounce Energy Blog

Foil-clad bubble wrap is a popular radiant energy barrier.

The foil barrier has a lower emissivity than paint, which is the amount of heat an object will emit as it is being heated. Emissivity runs from 0 ( a mirror) to 1.0 (a theoretical “blackbody”.) While painted roof deck does indeed block heat from radiating from the roof structure into the attic, the painted surface is also bonded to the roof assembly—which gets hot because this direct contact conducts heat right through the paint. Paint tests have shown its emissivity averages at 0.17. Meanwhile, foil radiant barriers that are stapled from rafter to rafter are separated from the roof deck by an air gap. Because foil radiant barriers have an emissivity at .1 or lower, up to 95% of the heat that radiates from the roof decking is stopped by the foil barrier. While the roof-facing side of the foil does get hot, the foil doesn’t emit as much heat into the attic space.

There are, however, two things to bear in mind when installing a foil energy barrier. One is that while double-faced foil might be advertised as extra-efficient, it’s not all that great. While one foil face might reflect 95% of heat back towards the roof deck, the side facing in can only reflect less than 5%. That second side only adds to the cost but not the efficiency.

The other thing for Texas homeowners to remember is DO NOT USE foil radiant barrier to cover insulation on the attic floor. It will act as a vapor barrier and trap moisture in the layers of insulation. That can lead to mold, mildew, and serious water damage. While some manufacturers tout radiant barriers as a type of insulation depending on it’s use, the real fact is that at best the stuff only has an R value of 1.

How Much Can You Save?

How to Shop for Home Improvement Projects - Radiant Energy Barrier | Bounce Energy Blog

A lot of research has been done on how radiant barriers can reduce the amount of summer heat gain in attics. Oak Ridge National Lab (ORNL) tests showed that for attics insulated to R-19, a radiant barrier could reduce the summer cooling bill by 2% to 10% depending on the amount of insulation you have in your attic. Because the insulation slows heating moving from the attic space down into the living space, the less insulation will see more of a benefit in their living space from a radiant energy barrier. Homes with a well-insulated attic will not notice the benefit as much.

However, many Texas homes are built with central air conditioning installed in their stiflingly hot attics . Consequently, keeping the attic space cooler can help the air conditioning cool your home more efficiently as well as extend the blower motor’s lifespan by reducing wear from running in too much heat.

What’s the Right One for Me?

How to Shop for Home Improvement Projects - Radiant Energy Barrier | Bounce Energy Blog

When you’re considering a radiant energy barrier, either paint or foil, there are several things you need to consider.

  • How much insulation do you have in your attic? If you have more than an R-19, chances are you’ll notice less change in your cooling bill.
  • How much do you want to spend? While foil barriers have been shown to be superior, paint costs less and has a lower labor/application cost.
  • Be wary of the sales people telling you radiant barriers are “equivalent” to insulation. It’s not the same stuff and doesn’t do the same job.
  • If you’re unsure about putting a radiant barrier into your attic, consider planting trees that will shade your roof, instead. Not only will the shade cool your roof, they also help cool the area around your whole home. Plus, they also increase your home’s curb appeal!
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