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RADIANT BARRIERS - ARE THEY BEING MISAPPLIED? VERY HOT TOPIC!!!

By
Real Estate Agent with Askins Realty Group, LLC 0599938
  • Retrofitting New Inventory Homes or Existing Homes can also be considered. I have found that www.foilbarrier.com provides the best Foil Radiant Barrier product solution in the DFW Metroplex. The work in the home below was performed by Foil Barrier. home Foil Barrier is operated by Joe Perry and he can be reached at 817-789-1057 or 214-762-3898.

Radiant Barrier Foil installed over attic insulation

Radiant Barrier Retrofit. Double layer added over insulation

GENERAL DISCUSSION

In the picture above foil radiant barriers have been installed over the attic insulation to prevent infrared radiation (IR) that is being retransmitted from the underside of the roof from striking the  insulation that sits directly over the living space below.

One of the requirements for a radiant barrier to work is that it must have an "AIR GAP" in front of the foil that is facing the source of incoming IR. That is why the barrier is on top of the insulation in the home pictured above and not glued or spray painted on the underside of the roof decking. Placing the foil over the insulation prevents IR that is being retransmitted from the underside of the boiling hot roof decking  from striking your attic insulation, thus helping the insulation over your living space stay cooler. I have been in countless homes and can tell you that the undersides of Texas roofs with or without a radiant barrier painted or glued to it becomes boiling hot during the summer months.

WHAT IS INFRARED RADIATION (IR)?

Infrared radiation is a frequency that has no temperature in and of itself until it strikes a surface where it then transmits heat energy into that surface. That is why space vehicles are "foil wrapped on the outside." In Deep Space the temperature is approximately -270 Celsius (-454 Fahrenheit) YET there is an exceptional amount of IR present.  This would suggest applying the foil over your shingles would actually give you the most beneficial radiant barrier effect and that is to reflect incoming IR before it can strike a temperature absorbing surface like your dark gray tar based composition shingles on your roof.

That is why a big Texas TREE is your best radiant barrier!

Think about it! The tree prevents IR from the Sun from hitting your roof's shingles! If shingles stay cool your attic stays cool. Once a surface gets hot, it begins to re-transmit IR as well as conduct heat within the material itself. In the case of a typical Texas house, that means IR is re-radiated from the underside of your roof decking plywood sheets into your attic insulation - NOT A GOOD THING! In my opinion gluing a radiant barrier to the underside of your home's roof decking does little as the physically attached foil quickly adjusts via "direct heat conductance through a solid" to the temperature of the HOT roof and acts like a huge hot radiator surface.

I know one of the the technical properties of a true foil radiant barrier is extremely low emissivity which means the hot foil has a very low rate of IR retransmission. However the hot foil can and does quickly heat up the attic air to very uncomfortable attic temperatures reaching to 130 F or higher. The point here is that homes with radiant barriers glued or painted to the underside of roof decking can still have hot hot hot attics that help to compromise a homes energy efficiency not to mention soak your AC system and ducts in scorching heat.

LOW EMISSIVITY CAN STILL BE A HOT PROBLEM!

Even if a major characteristic of a radiant barrier foil is low emissivity, which means when the foil itself gets hot it has a very low rate of retransmitting infrared radiation towards your attic insulation, the foil can still become a very hot surface and when you multiple a hot radiant barrier by the large surface area that most roofs represent, you still have a very hot attic. Just touching a radiant barrier in the hot afternoon will confirm the fact that foil barriers can and do get scorching hot.

As a Realtor, I have closely looked at a number of radiant barrier installations by a variety of home builders and I can tell you that some of the hottest attics I have been in had radiant barriers glued to the underside of the roof decking. What this suggests is that if you are to rely on the low emissivity principles of a radiant barrier to help you out you must also plan to have adequate attic ventilation working in tandem with the radiant barriers. At best the 'underside' radiant barrier becomes a time delay device for heat build up in your attic and if proper ventilation is not established the end result will most likely not have much of an effect on your AC bills.

So if you are going to retrofit a home and can't improve the ventilation aspects of your attic so hot air can freely circulate to the peak of your attic and out ridge vents, turtle vents, etc, then you should be considering installing the radiant barrier over your attic insulation.

This leads me to conclude that the primary intended purpose of the radiant barrier is not due to it's low emissivity characteristics, but rather to primarily defeat incoming infrared radiation by reflecting it away from surfaces directly underneath the foil barrier, hence preventing that surface from getting hot in the first place means an external barrier application over and not under a surface.

If inside radiant barrier foil applications really work (low emissivity principal) or are the primary intended use of a radiant barrier foil then why are space vehicles not employing the same technology the housing industry seems to embrace? The last time I checked, space vehicles all have the foil radiant barrier on the outside.

There are lots of opinions out there, and you have read mine, but  it seems more logical to shield your living space with a perforated radiant barrier foil directly on top of your attic insulation or over your roof's shingles if you are to realize optimal results from the use of radiant barrier technology. This way you preserve the required "air gap" needed for a radiant barrier to reject or reflect incoming IR Radiation before it strikes your insulation, or you can find a BIG TREE and place close to your house on the South West Side, but it will cost you much much more!

Good luck on getting city zoning approval for an external highly reflective radiant barrier over your roof shingles!

Comments (1)

Anonymous
Bill

You can install radiant barrier foil yourself from www.AtticFoil.com

Aug 07, 2008 04:45 PM
#1