I'm thinking about putting more insulation in my attic. The possibilities are more insulation on the floor of the attic, spray foam or cellulose, or radiant barrier under the roof deck. Several weeks ago I got an estimate: $3700 to spray 5" of open foam up under the roof deck. This is supposed to keep the attic about 10° warmer than the house. Wow, sounds great because the attic becomes a more usable storage space instead of baking stuff at 140°F! However when I called another contractor, I was told that open/closed foam was not allowed with gas water heater/furnace in the attic. (That's how they do it in Houston, no basement, furnace and water heater in the attic, although I'd prefer it in my garage but those are not big enough to put them there). So that's why this contractor offered cellulose insulation. And then there is radiant barriers, aluminum foil stabled to the bottom of the rafters that keeps heat out of the attic. Anyone familiar? I'm about to launch some net research to educate myself, but thought I'd ask here.