Is there a difference in heat gain in the house if you place the radiant barrier on the attic floor or roof section? On top of the studs, with a vapor space.
Some studies show that the typical reduction of the heat flux in the ceiling of the house with the radiant barrier installed on the roof rafters is around 25%. When placed on top of the mass in the floor, the reduction is as much as 40%. I believe the testing was done with an R-19 mass in the floor. Of course, over time, if dust collects on top of the radiant barrier on the floor, the thermal performance will be reduced, whereas no such reduction would be expected on the roof rafter installation.