Radiant barrier for new roof

My roof is about due for replacement. It has two layers of shingles on it, oldest is asphalt, top layer is corning fiberglass. Roof itself is plywood on 2x4 frames.
The 2 layers of shingles are going to come off and the plan is to use architectural shingles on the new roof.

Here is my question: rather than staple or spray some sort of radiant barrier inside the attic (which is very difficult in places because the roof has fairly shallow pitch, not flat but not Cape cod steep either--Think 1960’s tract house type), can a radiant barrier be attached on top of the plywood (either a spray paint type or the staple-on film) before the roofing material goes on?
If so, which is better, spray-on or paper type? And any suggestions on particular products?

BTW, I live in the Phoenix Metro area. Anyone who lives here knows why I am asking this question.

Thanks for any help and advice.

 

Radiant barriers require an air space to effectively reflect or not radiate heat. The need for an air space is why they want you to place it inside your attic. Above the roof deck, your options are first, choose a light color shingle to reflect the heat before it can toast your roof. Then, if you want the barrier up top, you would have to strap and add another layer of sheathing, with a layer of radiant material somewhere inbetween. The air gap formed by the strapping is what works in conjunction with the radiant surface to block the flow of heat. Here is a link that will explain better:
Radiant Barriers

Bud

 

Thank you for the link, Bud. Wow. Learn something new everyday. Guess I'll be crawling around the attic anyway (in January, that is.)