John

John,
I'm limited on height for a few reasons - the ledgers are already up (deck is in a corner of the house), I've got windows underneath the deck and a doorway above, and if the joists (and beam) get too low the patio underneath will be unusable.

I definitely see your point about things being too wet under the decking, but it seems like you would have the same issue with a torchdown roof - with the draped troughs I would think water would more easily be shed since it would flow to the middle of the trough and then drain out (water is less spread out than with a planar slope underneath).

I've seen deckman22 suggest using sheet metal under the deck as a roof, but after searching the archives haven't been able to find his full explanation of how to do so.

I've also considered using corrugated plastic under the joists screwed to a series of crosswise, graduated-in-size stringers. That way there would be air movement all the way around the joists.

I apologize for beating a dead horse, it's just that I hadn't seen anyone post about the draped-type underdeck roofing before.

Using a torch down would lower the joist height 1 1/2 '' or so no reason to change the ledger, in 14' a person would need 1'' of fall,the stringers run in the direction of the fall so water just runs off it nothing stayes underneith. Al has been using that glav. metal for a while now you could e-mail him I am thinking.

All the decking sitting on plastic is just asking for trouble. J

Okay, thanks John! I understand your point now, it's the wood on plastic that results in trapped water with nowhere to go. That makes sense to me.

I did email Al, haven't checked for a response yet.

When you say the joist height gets lowered 1 1/2", do you mean the total additional height is only about 1 1/2" taller? I'm thinking 2x10 joist plus 1/2" plywood plus torchdown material (minimal) plus 2x4 stringer plus 3/4" decking. Or do you lay those 2x4s flat?

Do you anchor the stringers in any way, or just let the whole system float on top of the torchdown? I guess you could just tie into the railing posts.

2x4s lay flat on strips of the torch down granulated up,thats just a little extra I do, 1/2'' plywood, 3/4'' decking yup that sounds right, if you cant make it work you cant make it work.

Do Not screw thru the stringers into the roof, in fact dont puncture the roof at all be real cearfull about that.. I usually dap out the post 1 1/2'' x what ever it takes for that dap to sit on the decking then install the post with high grade constustion adhesive and 1/2'' lags, another way would be to bolt thru with double nuts and seal tight, yet another way would be to use toggle bolts, it all depends on how much wood you are fastening to.

Execpt for the posts landing on the decking the whole thing is floating as you look at it that way, of course if you get a storm big enough to lift your project that deck is going to be the least of your problems. J