Replies

1. 
   Piffin | Oct 03, 2003 07:06pm | #1

   R-ratings or resistence to heat loss are vastly over-rated for radiant foils and films taken from results of testing in optimum lab conditions.

   When was the last time you saw an on-site installation of anything performed under laboratory conditions?

   These ratings depend on have an air space in front of the radiant barrier. If you are stapling to furring and then applying sheet rock immediately over it, in contact with it, you change it from a radiant barrier into a conductioon foil that draws thermal energy away from the warm side to the cooler side. Generally, this is an effet opposite of the intent of the installer.

   If you install on the concrete block and then place the furring over it to maintain a space, you may get some reflective benefit to resisting radiant heat loss, but I tend to doubt that it would approach 4.5. and it would not necessarily prevent the heat loss that comes with infiltration unless it were tightly sealed.

   The shame of this question is that it proceeds fdrom an increasing desire on the part of many people to reduce heat loss and increase energy efficiency in the face of rising energy costs. That demand is sparking an increase in what I regard as questionable products and sales techniques - enerquacks

   .

   Excellence is its own reward!

1. 
   fortdh | Oct 04, 2003 12:40am | #2

   You are dead on.Aluminum foil/kraft barriers in attics attached to the rafters with foil side down are very effective radiant barriers, and can reduce the attic heat load, but they are not insulation. They need 3/4" air space to produce their low emissivity (0.05). I see a lot of adds with the term "equivalent r-value" ....I would use foam board or conventional fiberglass batt over sprayed closed cell poly.Paul

   veEnergy Consultant and author of

   Practical Energy Cost Reduction for the Home

1. 
   Piffin | Oct 04, 2003 03:42am | #3

   If you don't mind, I'd rather be right-on than dead-on. There's too many funerals going on in my neck of the woods lately.

   Thanks

   ;).

   Excellence is its own reward!

1. 
   toast953 | Oct 04, 2003 09:12am | #4

   I always   figured you, for leaning to the Left, just a wee bit. eh, eh,,, You all be safe out there, Jim J

1. 
   Piffin | Oct 05, 2003 02:12am | #5

   Go right, young man, and you'll never go wrong.

   Excellence is its own reward!

2. 
   MikeR | Oct 06, 2003 06:26am | #6

   Piffin et al,

   Here in Florida they don't really use this as a "radiant barrier" style but more of an "insulative" style.  (If you can call it that?)

   Block is up, furring strips nailed to the block, then Al-Foil stapled to the strips and then drywall directly to the strips so it would be in contact with the Al-Foil and the air space (3/4" thick) would be between the foil and the block.  Is only used on block walls and never in the attics where other radiant barrier styles might be used.

   My question is I have been discussing this with some other folks as to whether the kraft paper is beneficial in our climtae or actually detremental?  We never put any kind of vapor barrier or things like Visqueen on the inside of a wall like you might do in our areas.  The debate now is if this kraft paper is serving as a vapor barrier and holding in moisture that should be allowed to permiate through the interior of the home and outward.

   I have mixed opinions on all of these thought but am interested in what you and others think.

   Thanks

   Mike