I got several calls and emails from last week’s post about installing radiant barrier under shingles.  It seems that I’ve kinda stirred up a hornet’s nest of sorts.  One roofer was grateful for “Saving” him from making a big mistake.  Another guy was down-right mad.  He said I didn’t know what I was talking about and that these products reflected heat because they are white or reflective to light on one side.  If you put white/foil or ANY reflective material on TOP of the roof, then yes it would help.  Under the shingles, conductive heat does not know what color something is.

Here is a video I made to illustrate how without an air space you can never have radiant heat.

 

Looking for more videos on this topic? Check out my posts below.

  • Thermal Proof Using RoofingFoil™ + Underlayment Under Metal & Tile Roofing
  • The #1 Attic Ventilation Problem
  • Enerflex® Radiant Barrier at Home Depot compared to AtticFoil® Radiant Barrier
  • Radiant Barrier Installation Summary – Block the Heat
  • Green Energy Barrier (and other products) Compared To AtticFoil® Radiant Barrier Foil
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    14 Comments to “New Video=> Let Me Show You Why Radiant Barrier Under Shingles Just Won’t Work”

    1. Bryan R says:

      I like how you explain this in the video. I had a guy try to sell me this stuff last year when I was having a new roof put on after a hail storm. It didn’t make sense what he was sayin would work.

    2. Lee says:

      Great video and really helpful information

    3. Jason says:

      So… What’s your take on LP Techshield? By most all accounts it works, but it’s attached to the decking? Forgive me if this is a stupid question but it seems to me that there’s no air gap between the foil and the roof deck in that scenario either?

      • Ed Fritz says:

        Techshield is a good product and I recommend it for new construction. The required airspace is actually the attic itself. Techshield or any other product applied DIRECTLY to the bottom of the roof deck is actually working off the LOW EMISSIVITY quality of the aluminum foil rather than the reflectivity quality. This is similar to wrapping a hot potato with foil to keep it hot. In general, if the air space is on the “hot” side of the radiant barrier it is working off of reflectivity. If the air space is on the “cold” side of the radiant barrier it is working off the emissivity quality. Here is a video on why an air space is required.

    4. Jason says:

      Thanks. Have to say the 2nd video really helped my understanding of your reply. Glad you included it, not sure I’d have gotten it otherwise.

    5. jeff says:

      The funny thing about this is I told a guy that I was trying to sell a roof to that it would not work but my competition said it would. He used them instead of me. I told him to use techshield. Hope he gets any of his money back in savings on his electric bill. LOL.

    6. Shane says:

      Have you tried out the Truprotect product. It seems like it would be an effective radiant barrier that you can apply directly to your roof because the corrugated board provides the air space. Foil, board, foil, board, foil, all laminated together.

      I have to redo an addition to our home that is a “rafter room,” and it is an oven in the summer. I have to find some way to insulate from the roof side. I’m thinking truprotect would be a good option…yes? no?

      • Ed Fritz says:

        Shane,

        This still won’t work. There is an air space INSIDE each layer of cardboard, but there is NO airspace BETWEEN the layers of cardboard where the layer of foil is installed. The foil has full and direct contact with the cardboard on the inside layers. The ONLY layers of foil that are effective as a radiant barrier in this product are the two outer layers. However, the minute you lay the product on something flat you eliminate the effect of the bottom layer and then if you lay something on top like shingles you eliminate the radiant barrier on top.

        The net result is you end up with a multi-layer of cardboard between the shingles and the roof deck. This will help some to reduce conductive heat flow through the roof assembly. Or, you could just install some cardboard or a thin layer of foam board to get the same result.

        It sounds like your “rafter room” is a cathedral ceiling. If your only access is from the outside (roof side), I would recommend installing ISO board (Polyisocyanurate Board) between the shingles and the roof. This is basically how commercial roofs are built. If possible, I would look to doing a ventilated skin roof with either tile, or metal so you can install a radiant barrier and still have the required air space.

    7. Gabriel says:

      Well, in my area in Texas, the xxxxx is pretty much the only one available in the area except by Special Order and the only one i have personal experience with, and so, its the only one i can personally vouch for. I’m one of the principals at a construction company and I did my homework before recommending it to our clients. The data seemed solid, it had its government certifications, and we went with it. Every One of our clients love it and are ecstatic we recommended it and are experiencing an average of about 40% reductions in utility bills. One client went from $1200 a month last April to $242 this April. So, while your theory sounds good, apparently that little white layer gives enough of an air pocket to do the job or there’s something else at work here, because it has definitely made a huge difference in each and every installation.

      • Ed Fritz says:

        Gabriel,

        Respectfully, there is no “air pocket”. My point is that physics is physics. Radiant heat by definition can ONLY travel across and air space (void, nothingness). Without an air space you cannot have radiant heat since you have a “solid”. If you look at their own information it says an air space is required to act as a radiant barrier. So, I am in agreement with the manufacturer. As for the energy saving – I’d agree with you – “…there’s something else at work” but it’s not the underlayment doing it.

    8. Bob says:

      I live in Phoenix, AZ, have a flat roof that needs to be replaced.
      Can I use a radiant barrier under a built up foam roof If I can figure out a way to provide an air space. I’m thinking of barrier, furring strip, plywood, foam.
      Will that work?

      • Ed Fritz says:

        Bob, It would be tricky to get an air space and radiant barrier below a foam roof. Since the roof is flat, I would consider adding a couple of inches of ISO board and then going over with single ply “Cool” membrane roof like http://www.Duro-Last.com

        This is an awesome roof for flat/commercial roofs. The roof has a high reflectivity and low emissivity. It acts like a radiant barrier by not absorbing much heat. You can walk around barefoot on a 100 degree day on these roofs.

    9. Mkat says:

      Ed I am building a outdoor pergola with open sides and a solid roof with shingles, will the Radiant Barrier boards help reduce the temperature under neath the pergola temperature are any where from 90 to 115 degrees.

      • Ed Fritz says:

        In an open pergola the actual AIR temperature won’t change much but the amount of radiant heat coming off the roof will be MUCH less. You FEEL the radiant heat. So, installing it is a good idea.

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