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by • January 21, 2011 • UncategorizedComments (4)2040

Radiant Barrier Walls for a Hot & Humid climate

If you google “radiant barrier” you’ll get a zillion hits about how you should use radiant barrier decking in your roof/attic assembly.  But, you don’t hear much talk about using radiant barriers on unshaded exterior walls.  One reason you don’t hear much about walls and radiant barriers is that it’s harder to build in the air gap needed to make a radiant barrier actually work.  If you embed a radiant barrier in a wall assembly (say behind siding up against the sheathing) it won’t function.  But, if you’re cladding your house in rock or brick you have that air gap behind the masonry and it’s a great place to use a radiant barrier.  This is especially true for our hot/humid climate when a house has unshaded south & west facing walls.  In this video you’ll see how we are using this technique in a very efficient Barley & Pfeiffer Architects home my company is building near downtown Austin, TX.  -Matt Risinger

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  • Hi Matt,

    Enjoyed your post, as always. Out of curiosity, why did they use that 3/4″ rigid foam sheathing? It would seem like overkill for Austin if they also used spray foam on the interior wall cavity and especially if they used 2×6 studs and closed cell foam. What was their design R value for the exterior walls? Regards, John in Houston

  • Hello Matt,
    Thank you for sharing your great wisdom and building science knowledge. I have learned a lot from watching your video blogs. I have a question about using radiant barrier on exterior walls. I am building a custom home in Charlotte, NC for myself and wanted to install the radiant barrier on South and West facing walls. However, I am concerned about negating the moisture permeability of the Tyvek HouseWrap by installing the radiant barrier on top of it. In this region, the code requires a vapor barrier on the interior of the wall. I have read that it is a really bad idea to put a vapor barrier on both sides of the wall. I do plan to make the walls fairly air tight by caulking/sealing all joints and gaps and insulating with Roxul mineral wool bats, covered with Certainteed MemBrane vapor barrier (a wall system similar to Corning EnergyComplete.)
    What are your thoughts on me installing the radiant barrier on the exterior walls? I appreciate your reply.
    Thanks.

    • Couple thoughts: 1. Be sure there is an air gap on the front of the radiant barrier or it won’t work. 2. Tyvek makes a radiant barrier version called Thermawrap. I’ve used it before with brick and had good success.
      What’s your cladding?
      See my post today using rigid foam R-Max as the radiant barrier. The video is called “Texas Deep Energy Retrofit”. Best Matt

  • Hello Matt,
    Thanks for the super fast response. My exterior cladding is brick veneer, with hard coat stucco on dormers and a small gable area above a hipped portion of the roof. Thanks for the recommendation on Thermawrap. I will see about getting that from my supplier.
    Regards,
    Jack.