Radiant Barrier – Things to Consider

Radiant Barrier has a long successful history as a way to reduce heat loads, but didn’t really get the deserved credit until NASA  acknowledged its use in the Space Program.  As a construction product; it is basically heavy-duty aluminum foil with at least one shiny side. For a greater understanding of the principles of this product, see  How it works? 

During the summer, an attic radiant barrier, combined with existing R-19 attic insulation, may reduce heat gain through the ceiling from 16%-42%. For single-story houses, typically about 15%-25% of the summer cooling load is due to ceiling heat gain. During the summer, the interior ceiling becomes a radiant heater adding heat to the interior spaces. The heat gain reduction from a radiant barrier installation will usually result in a total cooling load savings of 2%-10%-possibly as high as 15% in attics insulated to R-11 or less. Higher savings occur when retrofitting less efficient buildings. Buildings with little to no attic insulation and a high volume of attic ventilation typically provide the most dramatic energy savings from a radiant barrier. The hotter and sunnier the climate is, the more beneficial the radiant barrier installation becomes.

Types of Radiant Barriers

• Foil Faced Decking Material: With the trade name of TechShield, this radiant barrier product is applied to the back of roof decking during manufacturing and can be applied when the house is built or during a re-roof. Efficiencies of this product is in the neighborhood of 95-97%
• Rolls or Sheets: The sheets can be applied in a couple of methods; 1) Tacked up on the rafters or 2)rolled out on the attic floor. The labor makes these choices fairly expensive, but you can reduce the installed cost by making it a  DIY project.
• Spray on Solution:  This is a fairly new option, and came about because of the installed cost  of rolls or sheets. However, spray on radiant barrier is only about 65% as efficient as the aluminum foil types and lacks the low emissivity factor found in the other products. So it may have a lower installed cost, but your benefits will not compare to previously mentioned type.

Things to consider before purchasing or installing a Radiant Barrier

1. Climate: If living without air conditioning is not an option for you,  you may live in a temperature zone worthy of installing radiant barrier. Studies have shown, this product works better in very hot climates. If your attic regularly exceeds 130 to 140 degrees F, radiant barrier can reduce the attic heat load allowing your HVAC to work more efficiently , in-turn reducing your electricity consumption. If you live in climates similar to Arizona, Florida, or Texas,  you are probably a candidate for radiant barrier.
2. New Construction or Re-roofing plans: If you are considering either of these projects, foil faced roof decking can be purchased for a couple of dollars per sheet. This is the most inexpensive method to obtain radiant barrier. 
3. Attic Insulation: Make sure you have enough attic insulation, radiant barrier is not an insulation replacement product but just part of the equation. Having the proper amount of attic insulation combined with a radiant barrier product will provide the maximum benefit.  Also see Insulation: Do you have enough? and Insulation Choices.
4. Radiant barrier as a DIY project: Choose a product that has high tensile strength or is embedded with tightly woven fiber mesh; either of these features will reduce the opportunity for the product tear during the installation process. There is also a bubble pack version that appears to be as strong too. The bubble pack version is a great product for re-insulating HVAC ducts. Any radiant barrier product should be UL listed and/or have a NFPA “Class A”  flammability rating.
5. Location to place the radiant barrier: The following table shows a comparison of the effectiveness of the product applied in 4 different locations. Even though the attic floor application appears to be the most effective, this location may 1) cause moisture to collect under the barrier, 2) collect excessive dust; known to reduce its effectiveness and 3) add to the complexity to performing future work in the attic.  HomeownerBOB recommends avoiding using this product on the attic floor. 

Radiant Barrier Location	Whole House Tests		Test Cell Tests
	Mineral InsulationLab	Oak Ridge Lab	Solar Energy Cntr	Tenn. Valley Auth.
Roof: attached to roof deck	—-	—-	36 – 42%	16%
Roof: stapled between rafters	—-	—-	38 – 43%	—-
Roof: stapled under rafters	24%	25 – 30%	—-	23 – 30%
Attic Floor***	35%	32 – 35%	38 – 44%	40 -42%

If re-roofing is not in your future, installing the barrier on or under the rafters to gain the most long-term effectiveness is probably your best choice. Most of these products qualify as an energy tax credit so take advantage of the opportunity and get it installed before it gets too hot.

Reference Studys of Effectiveness of Radiant Barriers

1. TAMU Study
2. Radiant Barrier Fact Sheet; DOE Oak Ridge National  Laboratory