Waterproof Underlayment For Deck?

Cole

Guys, what can I lay under decking boards so that water will not penetrate the plywood underneath?

I will need to nail 2x4 sleepers to the top of it for the deck boards.

I was thinking I&W Shield but it says it is not recommended for low slope applications.

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tinner666

Not sure what you're asking. What plywood under what deck boards? Is this a 'deck' for people with plywood underneath for some reason?
Or a roof deck that's getting sleepers for a metal roof?

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Frank Slate Roof Repairs, Richmond, Va.

Cole

Well it is a carport/deck. The deck is on top of the carport.

When the job was done 10 years ago, they used plywood on top of the joists and then came with a layer of 30 pound asphalt and then laid 2x4 sleepers down on it for the deck boards to nail to it. It does have a 1/8" slope to the front, which is where the water leaves.

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tinner666

Put 2 layers of mod-bit, plain down, then apply 1 layer of granule-surfaced mod-bit.
You're not looking for an underlay, you were looking for a type of roof.

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Frank Slate Roof Repairs, Richmond, Va.

Cole

Frank, thank you.

I am not a low slope roofer so this was out of my league. I will take what you have said and run with it.

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jmorgan

Dont nail or screw the sleepers through the new membrane. Loose laid sleepers are fine.
\Jim

theroofinggod

tinner and jmorgan are right,but typically we add strips of mod bit under the sleepers too so they don`t bite into the roof over time

tinner666

Thanks TRG and jmorgan. I do some things so naturally, I forget to point them out or even mention them. Both are what I do, but I forgot to mention them. And the question of railings hasn't even reared it's head in this thread yet. But we know it's coming!

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Frank Slate Roof Repairs, Richmond, Va.

theroofinggod

notch them over the roof and secure them to the fascia w/carriage bolts