radiant barriers in attic

A radiant barrier is one of many measures used to keep heat out of the home.

Paul Proctor is CEO of R E Roofing and Construction, Inc.

Guest post by Paul Proctor of R E Roofing and Construction, Inc.

If you’re concerned about your home’s energy efficiency, you’ve probably heard about radiant barriers. But what do you actually know about them? Do they really work? And how should they be installed? In the following article, we’ll address these and other questions about radiant barriers.

 

The impact of solar radiation

Before learning about radiant barriers, it’s helpful to get an idea of how solar radiation affects temperatures in the home. As explained in an article published by Green Builder Media, radiation from the sun travels through space, enters the Earth’s atmosphere and eventually hits our roofs. It’s estimated that the amount of unfiltered radiant energy that strikes one square foot of roof surface is about 250 BTUs. If you take the average roof area of 3,000 square feet and divide that by two (since typically only half of a roof’s surface gets direct sunlight), that creates a whopping 375,000 BTUs. To gain some context, consider that the average stove range has about 7,000 BTUs per burner. In a word: hot!

Unfortunately, all that heat accumulating on the roof doesn’t just stay there—it radiates into the attic and eventually ends up in the living area of the home. In many cases, this requires a lot of air conditioning. Specifically, to offset 375,000 BTUs of solar heat gain, you’re looking at more than 31 tons of air conditioning! In terms of energy bills, that’ll take a big bite out of the average wallet.

The impact of solar radiation is further exacerbated by the fact that many homes’ attic air ducts contain leaks. This causes the ducts to draw in and distribute hot air throughout the home, which requires the air conditioner to work even harder. The result: more energy consumption and more money spent.

 

Measures to combat solar heat gain

Fortunately, there are several ways to allay the effects of solar radiation on the home. These include supplementary measures like insulation, ventilation, roof materials, air duct and attic sealing, and, of course, radiant barriers. However, since all of these measures play an important role in reducing in-home temperatures, it’s worth looking at each before we discuss the one at hand.

  • Air duct and attic sealing not only improves energy efficiency, it’s the best way to improve a home’s indoor air quality. You can have your air ducts tested for leakage at any time (and, if necessary, repaired). However, measures to prevent leakage from other areas of the attic can only be implemented during initial construction or a reroof project when the roof is removed and all areas of the attic are accessible.
  • Insulation traps much of the hot air from your attic and prevents it from migrating into the living space below. In the Bay Area, depending on the climate zone, R-30 to R-60 attic insulation is required for new homes and a recommended upgrade for existing homes.
  • Ventilation is the means by which hot attic air is removed from your home. This can be accomplished with properly sized and situated passive or power ventilators. The appearance and effectiveness of ventilators can vary, so you’ll need to do some research before choosing. Installing and/or upgrading ventilation is usually done at the time your home is built or during reroofing.
  • Roofing materials are a major determiner of how much solar radiation is permitted to enter the home. Today, all roofing materials are rated for solar reflectivity; the higher the rating, the more energy-efficient the materials will be.

 

Understanding radiant barriers

And now, let’s look at radiant barriers. A radiant barrier is a shiny, foil-like material that reflects radiant heat from the sun. It’s typically installed in the attic, just below the roof, where the majority of radiant heat enters the home. Radiant barriers are available in rolls; laminated onto sheets of plywood, OSB and rigid insulation; or as a spray-on substance.

Of course, the big question is, “Do they work?” In theory, yes. Depending on the circumstances, a radiant barrier can lower the temperature in an attic by 20 to 35 degrees Fahrenheit. However, this doesn’t mean the temperature of the home will be that much cooler. As cited by the author of the aforementioned Green Builder Media article, following an application of a spray-on radiant barrier, he saw a 20 F drop in his attic’s temperature. This translated to a mere 2 F drop in the temperature of his living space. Clearly not a huge difference, but a difference nonetheless.

In terms of your own home, the next question on your mind is likely:

“Will I benefit from installing a radiant barrier?”

How much you’ll benefit from a radiant barrier will depend on two primary factors:

  1. Environmental factors and supplementary measures

If your home is well-shaded during much of the day, a radiant barrier likely won’t be worthwhile, as there isn’t much solar radiation hitting the roof. Additionally, if your home is well-ventilated and well-insulated, with well-sealed air ducts and an energy-efficient roof, a radiant barrier may not have much of an impact. However, if your home lacks these measures, a radiant barrier can provide an affordable, easy-to-apply means of supplementing them.

  1. Correct application

For a radiant barrier to perform effectively, it needs to be applied properly. For example, there must be an airspace of at least one inch between the radiant barrier and the underside of the roof. Since there is currently no universal building code governing the application of radiant barriers, you must rely on your local building department (most of which have not yet established their own guidelines) or the good practices of your builder or roofing contractor.

To summarize, a radiant barrier can be a helpful measure to reduce temperatures in the home and, in turn, the need for supplementary air conditioning. However, a radiant barrier’s effectiveness is dependent upon a variety of factors, including climate, roof efficiency and proper installation. Also, a radiant barrier is just one of several ways to reduce home heat gain, so be sure to consider the full spectrum of your options.

To read more contributions from Paul Proctor, visit his Diamond Certified Expert Contributor Profile. He also contributed this previous guest blog.

 

Photo credit: Jason Dale ©2014, shared under a Creative Commons Attribution-Share Alike 3.0 Unported license

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