Roof Plywood Thickness Under Aluminum - How Thick?

[Tommy2tone_1999]

I will be using luan plywood for my roof. I will seal it with CPES, then I will be rounding the seams and sealing them with fiberglass tape followed by painted 0.04" aluminum. My question is how thick should my roof be under the aluminum - will one 1/8" sheet of luan be enough or do I need to go with 2?

[tony.latham]

I will be using luan plywood for my roof. I will seal it with CPES, then I will be rounding the seams and sealing them with fiberglass tape followed by painted 0.04" aluminum. My question is how thick should my roof be under the aluminum - will one 1/8" sheet of luan be enough or do I need to go with 2?

In Fredrick's Build Manual, he says one layer of 1/8" is fine under aluminum, but two layers if it's not sheathed. In my experience (build #3), 1/8" baltic birch ply is fine (('m backing mine with pink or blue foam which really strengthens it up) under .040 aluminum

Tony