Replies

1. 
   Riversong | Oct 31, 2010 06:37pm | #1

   Not if it's installed on the attic floor, since it will be a wrong-side vapor barrier and it will get covered with dust and lose its reflectivity.

2. 
   Robert Hronek | Oct 31, 2010 11:06pm | #2

   You are better off spending the money on air sealing and beefing up the insulation. Reflective barriers work the best when a building is not well insulated, But the reflective barrier will only help reflect radiant heat, it does nothing to stop conduction or convection. If your house is not air sealed and does not have at least the code R value for your area then that is where you need to start.

   With the home well insulated then there is very little benefit to reflective barriers, to the point it will never pay for its self.

   The Oak Ridge National Laboratory website has information on radiant barriers. It has a Radiant barrier savings calculator, It allows you to insert some parameters such as the amount of insulation. Adjust the amount of insulation up and it shows how little benefit there is from a radiant barrier.

3. 
   Riversong | Oct 31, 2010 11:37pm | #3

   Radiant barriers in attics do little to control heat loss but can do much to control solar radiant heat gain in the summer. But the barrier has to be installed on the underside of the rafters with the foil facing downward to prevent dust accumulation. Combined with thorough soffit-to-ridge roof ventilation, it can be a cost-effective way to limit radiant heat gain into both the attic and the conditioned space below.

   Radiant barriers are also very effective to decouple a floor assembly from the cold ground of an uninsulated or vented crawl space, and the work best for limiting heat conduction when in a floor with heat loss downward (offering as much as R-9 in insulation value).

   A radiant barrier under a wood floor radiant heating system will help considerably in reflecting heat back up to the floor instead of allowing it to warm the ceiling below.

   But those are the only effective uses of radiant barriers. And foil-faced kraft paper works as well as the much more expensive bubble foil products, while costing very little for either material or installation.

4. GBA Editor
   Martin Holladay | Nov 01, 2010 09:17am | #4

   Walter,
   The previous posters have provided you good advice. If you want more information, check out Radiant Barriers: A Solution in Search of a Problem.