Insulation, Radiant and Vapor Barriers - Insulating attic rafters??

I have a customer that has 6" of batt insulation in between the floor joists in the attic. Living in southern Cal. I believe that is suffecient. But he wants to deck the attic for storage and insulate the rafters. My research indicates that the silver radiant barrier insulation is better and more cost effective than the foam. Insulation has never been my big thing so any insight will be helpful. Thanks in advance!!

BBWOLF5:D

Hi big bad, here is a link that will cover some of the does and don'ts.

Welcome To Home Energy Magazine Online (http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/95/950309.html)

Bud

If your attic is ventilated, you should use radiant barrier rather than bulk insulation on the roof. Your roof is not your "thermal envelope" the ceiling is the thermal envelope. This (the ceiling) is where you want the insulation. Putting radiant barrier on the bottom of the roof deck will do just as good a job at reducing attic temperature and cost less.

All you really are looking for is shade. If you had an big, thick umbrella, would it keep you cooler in the Summer? No, since air is flowing on both sides. Ambient temperature is about the best you can hope for in an attic. Putting insulation on the roof is like having a jacket 2 feet away from your body??? Insulation does not "insulate" unless it is in contact with something you are trying to keep hot/cold.

Instructions on installing radiant barrier foil: Do-It-Yourself Radiant Barrier Foil Insulation - AtticFoil.com (http://atticfoil.com/foilinstallpics.htm)