Decks, Patios, Porches and Docks - Converting deck to screened porch

I am planning to convert my deck into a screened porch. I have posted preliminary plans here:

http://i257.photobucket.com/albums/hh224/3furrykids/porch/porchexport.jpg

The support posts will be 4x4. All exposed material will be either stained or painted. I am considering using ScreenTite over the posts, or they will be capped with 1x4 batten boards.

What type of lumber is recommended for the posts? PT? Fir? Redwood?

My deck railing posts, which will be removed, have warped over the years, they were pressure treated. I guess I'm afraid of the same thing happening to the 8' posts. Any suggestions appreciated.

Thanks,
Brian

Not sure where you are located, but one problem you may run into is underpinning or foundation requirements. If it is as low to the ground as your drawings indicate, I would pour a continuous footing on the 3 support sides, build a block wall and just build a room using standard construction methods. 4x4 will give minimal support, and may be nixed in opposition to using 6x6's by your authorities.

Larry,
Thanks for the reply. I am fairly certain that the deck foundation is solid, but I'll be submitting plans to the county and will follow their guidelines and recommendations.
A few people have suggested to me that I convert the deck into a full room or at least a sun room with large sliders. We live near the Chesapeake Bay in Maryland, and in fact a tributary is just a block away. Mosquito season starts in May and goes straight through September, and it is brutal. It really is impossible to enjoy the deck at that time, but we want to be as close to the outdoors as possible. This is what I have in mind:

http://i257.photobucket.com/albums/hh224/3furrykids/porch.jpg

I'll be using untreated wood for the roof structure as it will be protected, I'm just not sure about the posts. They will be painted or stained. What type of wood would a pro coming in to do this job use?

Pressure treated posts typically don't warp noticeably when used under a roof, especially when sealed with paint or stain. I've got a cabin in the mountains of NC, and the back porch is supported by 6X6 PT lumber. Between the porch floor and the roof, 4x4 PT posts were used. I don't have the exact measurements, but the 6X6 posts are around 16' (not counting the portion set in the ground,) and the 4x4s are 8', all of this is exposed and endures periods of high and low humidity/temp. The structure was built to withstand 100+ mph wind as well, (which only means some beefed up hardware in my case.)

If I can find a photo of it I'll post a link, but it hasn't warped yet.

Keep in mind I'm not a seasoned pro, but I've built several porches similar to what you're planning using PT lumber with very good results.

Sorry for taking so long to follow up with a pic. You're probably already close to finishing your project, or you may be finished.

It's a 4 hour drive to get to my cabin, and with gas prices the way they are, I don't get to go as often as I'd like.

Anyways, here's a pic of my porch/deck.

http://www.katanapg.com/picture/67372

I sort of told a lie, the 6X6's aren't 16', well, maybe one is. Still, they span quite a distance, and despite prolonged exposure to some pretty serious elements, the only complaint I have is that there is some splitting occurring. However, the deck-boards are the only components that are stained, the posts haven't been stained. So the cracking wouldn't have been a problem if it was stained or painted properly.

Cheers,
Jeffrey