I have an existing 16x16 deck that I'd like to screen-in. I'm confident with how the deck is anchored and it's stability. My concern is I'd like to not have to dig more footings for more posts to go up to roof level. My question is: Will the roof be adequately stabilized by "tieing-in" the roof structure to only the existing deck structure? (the roof will also tie in to the roof of my house, and slope in one direction only...to the backyard)

 

It's difficult to say since you don't describe how you plan to "tie" things together. Talk to your local building department. They can give you a valid opinion. (My instinct tells me that they won't go for it.)

 

The deck posts are 6x6, anchored to concrete footings. I have a doubled 2x12 beam fastened with hurricane ties on top of these 3 6x6's. 2x12 joists are fastened on top of the beam (again with hurricane ties) and cantilever 4' past the beam. The rim joists are doubled 2x12's.
I would notch 4x4's or 6x6's the depth of the rim joists and lag bolt them, at 4' spacing, which would land a post on either side of the deck on top of the 6x6's anchored to concrete. The top of the posts would be "sandwiched" with 2x10's and lag bolted. Then, a typical roof system consisting of 2x6 or 2x8 roof trusses running from the houses roof to the 'front' of the deck.
The only difference I can see is that those posts would run all the way to the ground. Is that such a substantial difference? I'm not trying to be argumentitive, just postitive the extra work is necessary. Thank you for your previous response, and your time.
Jim