Ceder Deck joists


I am building a deck that floats on a low slope 12 by 24' roof with a pitch of " per foot. The roof and porch have been designed and built to accept the weight. I will cover the roof with an EPDM membrane.
I am just looking for best guesses. I would like to have the deck flat by using tapered 2X joists from 2" to 6" to match the roof slope. I can not go any wider then 2" on the skinny end of the rafter. I am concerned about cutting and using green treated thinking the skinny ends will dry and warp before I get the composite decking attached/screwed? Cedar would be an easier wood to work and not have the problems of green treated. But will it last as long as treated if I put a finish on all sides? Is 20 years overly optimistic given that it is on the north side of the house? thanks
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snipped-for-privacy@dva.state.wi.us wrote:

Do they make composite 2xs? If yes can the be bought wide enough to rip 2 joists from one board? Then You would never have to worry about treating the cedar or any wood near the epdm and harming that in the future..The composite deck boards supposedly will last "forever",,the joists might as well too if possible.. Dean
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Dean wrote:

How long are you going to wait before you deck it? I would use treated. If you really want longevity, use .60 treated. I don't think warping and twisting will be a big problem unless you leave them laying on the roof for a long time before you deck. Cedar would be a big expense and unnecessary IMHO.
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