As it's already been said, this Forum is rife with mis-information. And the mis-information INCLUDES your statement: "You guys talk funny... we don't." I'd like to know where you get THAT mis-information. Maybe I have mis-information like you because I'd say YOU guys talk funny... we don't. Go figure.
I, personally, don't know of an UNDERSIDE radient barrier that you describe. With all this goings on, no one has stated a product or a manufacturer. From there, anything said about research and so on is moot. And we're talking about a shingled roof with wood sheathing (BIG assumption on my part so I could be wrong on the 'wood' aspect ...) Anyway, if you're gonna tout an UNDERSIDE, radient product, put it up so I can educate myself w/o having to rely on third party testimony. And according to Bill, the immediate TOP of the roof will get real hot but by the time you get to the UNDERSIDE, it's relatively cooler. Now, with that, put a radient barrier up. Where does the heat go??! If there's a radient barrier, then obviously, the heat's gonna be reflected back where it came from. And in between the outside of the roof and the radient barrier is sheathing. Are you really telling me that physics says that the sheathing will STILL be cooler on the UNDERSIDE with a radient barrier installed? It's impossible - then if it's possible, it isn't a radient barrier.
In the bonfire example, you stand in front of the fire, then put a piece of wood in front of your face. After some time, the heat begins to 'bleed' through the back side of the wood. BUT, between your face and the back side of the wood, is air. That air is the next thing that begins to heat up because it's COOLER than the back of the wood in front of your face. Now, put yourself in a space suit with a piece of wood as a mask, you're gonna cook because there's no place for the heat to go once it 'bleeds' through the wooden mask. (That's what it sounds like this attic is like.) At some point, the inside of the suit is gonna get so hot that the heat is going to begin to radiate BACK through the wooden mask to the, now, COOLER outside... No? If not, then where does the heat go?
This is why I want someone to cite some 'material' or a 'mfgr.' so I can see what I'm missing here. It doesn't make sense and I don't care WHERE you're from.
Are you still harboring some sort of 'grudge' by referring to people that live in a different part of the country as Yanks??! I thought the Mason-Dixon line was in Delaware somewhere. You mean no one builds homes below that line w/a basement??! Maybe you need to take a vacation outside your area code. You're living a deprived life.