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Understanding Radiant Barrier Under Shingles

Updated on October 29, 2013

Thinking about installing a radiant barrier under your shingles? A radiant barrier can be an extremely effective way of reducing heat gain in your home and increasing energy efficiency - but as with so many things, it only works if it's done right. It sounds simple enough - you're re-shingling your roof, so why not just layer the roofing felt, some radiant barrier foil, and then the new shingles? Presto, instant radiant barrier, right?

Unfortunately, no. While it can be done, a quick lesson in simple physics will show you why installing a radiant barrier under shingles isn't quite this easy. Radiant heat, by definition, is the transfer of heat from one item to another without touching. To be technical about it, radiant heat is electromagnetic radiation that travels in a waveform across a void. Ever hold your hands up to a fire? You feel the warmth of the flames, but you're not touching them - that's radiant heat. Radiant heat does not exist without space between objects, and without radiant heat you have no radiant barrier. When you simply layer radiant barrier foil and shingles with no space in-between, you're dealing with conductive heat instead – the type of heat transfer that would happen if you actually put your hand in the fire. Conductive heat cannot make a radiant barrier.

Although professional roofers should know better, some persist in offering foil-coated roofing underlayments, such as Polaralum®, as a radiant barrier. These roofers – whether mistaken or willfully misrepresenting the product – are trying to sell you something that doesn't exist. No product can work as a radiant barrier when placed directly under shingles, even if it is designed to be a radiant barrier in other situations. In fact, the manufacturer of Polaralum® clearly states that their product acts as a thermal barrier on roofs – not a radiant barrier.

While installing a green energy barrier is not as simple as just adding an extra layer to the shingling process, it can still be done economically and with a minimum of fuss. What you need to do is create an air space between the radiant barrier foil and the roofing material. Some roof types, like standing seam metal roofs and barrel-type roofing tiles, naturally have an air space between the roof deck and the roofing material.

You can also use wood battens to create the necessary space. After you have covered the roof deck with roofing felt and a layer of perforated radiant barrier foil, simply install the battens according to the manufacturer's instructions. The roofing material can then be attached over the battens, maintaining an air space between the foil and the shingles. To allow for maximum airflow, “notch” the battens or leave spaces between them.

Installing a radiant barrier as part of your new roof can be a smart move, but only if it is done correctly. An effective radiant barrier is like built-in shade for your roof – it will reflect heat away from your home, lowering energy costs while increasing comfort. Just be sure that you're truly receiving a radiant barrier and not simply shelling out money for an extra layer on your roof that actually provides no additional benefit.

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    • profile image

      Danny 

      4 years ago

      So explain to me how I put it under my shingles when I re-roofed my house and it worked? lowered my attic temperature and the temp in my home significantly.

    • Better Yourself profile imageAUTHOR

      Better Yourself 

      5 years ago from North Carolina

      Kelly - Glad the hub was helpful for you in coming to a decision on your new roof. Thanks for stopping by my hubpages!

    • profile image

      Kelly 

      5 years ago

      oH so very glad I googled this - we are getting ready for new re-roof and the contractor bid Polaralum - which - after reading this post- is a waist of money - we should foam insulate the rafters instead.

    • profile image

      neville 

      6 years ago

      There is some truth and also some misinformation in this article. The "simple physics" is far oversimplified. I happen to be a physicist as well as a building contractor. Radiant energy, whether in the visible spectrum or otherwise, must first be absorbed in order to be mechanically transferred as conductive heat. There is insufficient thermal mass in the aluminum sheet to hold and re-radiate any heat. Some products, notably Polaralum, are primarily NON-conducting with a very thin layer of reflective aluminum. For the non-physicist, "the proof is in the pudding" so to speak. Although many shingle manufacturers have explicitly approved this type of product for under-shingle use, there are certain types of shingles that will be destroyed by the excess reflected heat (a certain amount of the original radiant heat was absorbed by the shingle on the way in, and the excess is what goes into your attic/house and heats it up - this is what the barrier is reflecting and the shingle will absorb a portion on the way out). Class 4 (or impact-resistant) shingles made with SBS-modified asphalt composition will overheat and blister if installed on top of a reflective barrier such as Polaralum.

      I agree that the batten system will increase the insulative quality of the roof by creating an air gap (similar to dual-pane windows, though not sealed) that will keep the outside air temps from coming inside, this is a secondary issue - the point of the reflective heat barrier is to reflect radiant heat. It does not stop conductive heat transfer, neither does it create it. However, if you choose to use battens, note that the article does not explain the whole procedure. For rigid metal roofing (Decra, etc.), slate, faux slate, wood shake, etc. battens alone proper. However, you cannot properly install asphalt composition shingles on battens. A new deck has to be laid on top of the battens, and then the shingles may be installed on top of that.

    • Better Yourself profile imageAUTHOR

      Better Yourself 

      6 years ago from North Carolina

      Hey Marta - Our apologies - that video has been taken down, and here is the new video to help you. http://www.atticfoil.com/install-questions/using-u...

    • profile image

      Marta Ramirez 

      6 years ago

      Hello again. I am trying to see the video on how to install the radiant barrier, but the video is private. I tried to sign with my gmail account but still cannot see the video. I was talking to the roofer and he says that the shingles has to be attached directly to the barrier (deck- felt- barrier- shingles). How can he leave the space in between the barrier and the shingles (GAF Timberline 30yr shingles)? Thanks in advance for your answer.

    • Better Yourself profile imageAUTHOR

      Better Yourself 

      6 years ago from North Carolina

      So glad it was helpful for you, Marta! All the best with getting your new roof :)

    • profile image

      Marta Ramirez 

      6 years ago

      Thank you soooooo much for this information. Now I can make a wise decision when choosing the right company to do the roof in my house. Different roof companies have given me estimates and all of them tell me different things. Thanks to Google that I found your information.

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