Radiant barrier

A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer.

[1] In 1860, the French scientist Jean Claude Eugene Peclet[2] experimented with the insulating effect of high and low emissive metals facing air spaces.

[3] Peclet experimented with a wide variety of metals ranging from tin to cast iron, and came to the conclusion that neither the color nor the visual reflectance were significant determining factors in the materials’ performance.

Peclet calculated the reduction in BTUs for high and low emissive surfaces facing into various air spaces, discovering the benefits of a radiant barrier in reducing the transfer of heat.

In 1925, two German businessmen Schmidt and Dykerhoff filed for patents on reflective surfaces for use as building insulation because recent improvements in technology allowed low emissivity aluminum foil to be commercially viable.

[2] Within 30 years, radiant barrier was making a name for itself, and was included in projects at MIT, Princeton, and Frank Sinatra’s residence in Palm Springs, California.

[4] A metalized film was used to protect spacecraft, equipment, and astronauts from thermal radiation or to retain heat in the extreme temperature fluctuations of space.

Since the 1970s,[4] sheets of metalized polyester called space blankets have been commercially available as a means to prevent hypothermia and other cold weather injuries.

Since the thin coatings are fragile and can be damaged when exposed to air and moisture, manufacturers typically use multiple pane windows.

If an air space is not present or is too small, heat will conduct from the radiant barrier, into the substructure, resulting in unwanted IR shower on lower regions.

Manufacturers of this installation method often tout the savings in labor costs in using a product that serves as roof decking and radiant barrier in one.

While this method can be more effective in the winter[12] there are a few potential concerns with this application, which the US Department of Energy[11] and the Reflective Insulation Manufacturers Association International[10] feel the need to address.

The vapor transmission rate of the radiant barrier should be at least 5 perms, as measured with ASTM E96, and the moisture in the insulation should be checked before installation.

Lastly, this method allows for dust to accumulate over the top surface of the radiant barrier, potentially reducing the efficiency over time.

According to a 2010 study by the Building Envelope Research Program of the Oak Ridge National Laboratory,[13] homes with air-conditioning duct work in the attic in the hottest climate zones, such as in the US Deep South, could benefit the most from radiant barrier interventions, with annual utility bill savings up to $150, whereas homes in milder climates, e.g., Baltimore, could see savings about half those of their southern neighbors.

Performance testing by Florida Solar Energy Center[8] demonstrated that the increase in temperature at the hottest part of the day was no more than about 5 degrees F. In fact, this study showed that a radiant barrier has the potential to decrease the roof temperature once the sun goes down because it prevents heat loss or transfer, from the attic, through the roof.

RIMA International wrote a technical paper on the subject which included statements collected from large roofing manufacturers, and none said that a radiant barrier would in any way affect the warranty of the shingles.

A study by the Tennessee Valley Authority[15] mechanically applied a small amount of dust over a radiant barrier and found no significant effect when testing for performance.

However, TVA referenced a previous study which stated that it was possible for a radiant barrier to collect so much dust that its reflectivity could be decreased by nearly half.

Wrapping a house with radiant barrier can result in a 10% to 20% reduction in the tonnage air conditioning system requirement, and save both energy and construction costs.

A study conducted by CMHC (Canada Mortgage & Housing Corporation) on four homes in Paris, ON found that the performance of the bubble foil was similar to an uninsulated floor.

[18] The effective insulating value depends on the number of adjacent dead air spaces, layers of foil and where they are installed.