The Science

OTHER APPROACHES:

  • attic insulation (more)
  • wall insulation (more)
  • air sealing (more)
  • duct sealing (more)
  • HVAC tuning & upgrades (more)

You may have heard that radiant barrier insulation is "used by NASA," or that radiant barriers are a "space-age technology." Attractive as this may sound, the way that radiant barriers work here on earth isn't really all that spectacular. Here's a quick run-down of what they are, how they work, and why they may not be the best investment for your home.

What Are Radiant Barriers?

A radiant barrier is a building product that can help keep a home cool in the summer by reducing the amount of radiant heat gain that enters the home. They're typically used in the attic, and are intended to keep your attic cool by reducing the amount of radiant heat entering the attic from the hot roof. When your attic is cooler, the theory goes, your whole house stays cooler.

They're not necessarily a bad product, and can be pretty effective in hot climates, where the cooling season (the season in which you run air conditioning in your home) dominates the year. In southern states, for example, they're running air conditioners for much of the year, and keeping the attic cool is a high priority.

How Do Radiant Barriers Work?

attic heat gain without a radiant barrier
attic heat gain with radiant barrier
Diagrams courtesy of Energy Vanguard.

When the sun beats down on your roof, your roof gets hot. Since, according to the second law of thermodynamics, heat likes to move to cooler places, some of the heat from your roof moves into your attic. Since a radiant barrier has a low emissivity compared to other materials on the roof structure (plywood, etc), it slows down the transfer of radiant heat from the roof into the attic.

So What's the Problem?

In northern climates that are dominated by heating, a smaller portion of the energy costs of most homes is dedicated to cooling because of the short cooling season. There is also a much lower cooling load than in a state like, say, Florida. In short, the energy savings that you may achieve by installing a radiant barrier in a home in Texas or Florida could not be replicated in a northern climate zone.

According to the Oak Ridge National Laboratory, "... In the northern climate zones, the savings drops further, going from about $40 to $10 per year as you go from Chicago to Fairbanks... If there are no ducts or air handlers in the attic, the savings are much less, going from about $20 per year in Miami to $5 per year in Baltimore..."

If projected savings are only $5 per year in Baltimore, savings in Connecticut and other northern states will be even less. This doesn't exactly speak well of the economics of radiant barriers in northern climates.  

Other Considerations: 

According to research by the Florida Solar Energy Center, the effectiveness of radiant barriers decreases as more insulation is added to a home. So if your home is already insulated, you won't gain much by installing a radiant barrier. 

The consensus among building scientists is that radiant barriers are not a good investment for homeowners intending to increase the comfort and energy efficiency of their homes. See our resources page for further information.

North American Climate Zones (Oak Ridge National Lab)

In southern climate zones, retrofitting a home with a radiant barrier can make sense. In the north, it probably doesn't.
Image source: Oak Ridge National Lab