Radiant barrier decking (like TechShield) works and can actually be quite economical if you are having a new roof deck added. (Learn more about the difference between AtticFoil and TechShield here) The foil is applied to the plywood and then laid face down (toward the attic space) as it is installed. This application leaves the foil with an air gap (the attic space) so the foil works to block radiant heat from emitting (emissivity) into the attic space, and ultimately the home.

Another alternative to radiant barrier decking is to install the foil below the roof deck before the deck is laid (as shown here).  

The 60" wide radiant barrier roll is great for applications like this since it is the widest roll and you can cover more space faster. You can also use the 48" wide standard width radiant barrier, if that is more convenient for your situation.

Buy radiant barrier foil 

Installation

Second, the installation creates a channel between the roof deck and the foil that promotes air flow and proper ventilation. Ventilation goes a long way toward having a lower attic air temperature and an overall more comfortable space.

When installing the radaint barrier foil under the decking, you want to start the foil about 6 inches up so the foil sticks past the sheets of decking. Then you can put in foil as you go up and stop the foil about 6" to 12" from ridge or hips.

Here is a close up where you can see the foil is pulled/draped down about 4" from the deck. Installing the foil this way gives the air a chance to flow both between the roof deck and the foil and below the foil from the attic side.  

More Radiant Barrier Applications