Imo there are a lot of composite decking that is better than Trex, Premier, Timbertech, Boardwalk, Evergrain just to name a few.

There are ways to use metal roofing under your deck to waterproof underneath. I don't have time to go into it now, but if you email me I can run the process by you later. It's a lot less expensive than any systems that I have seen.

deckman2@hotmail.com

Slucci, I was wondering if you had any luck in finding an under-deck drainage system? I just had a composite deck built, and am interested in using part of it as storage (I was hoping to take advantage of the space underneath the 8x8 section that wraps-around to my back yard). I took a look at the original link you posted, plus another product called 'Rain Escape' and while they both look pretty nice, I'm guessing they are somewhat expensive and would probably be overkill for what I need. I don't care if it has that 'finished ceiling' look for example, (although that would be very cool! :-) given its location and intended use. I just want something to keep my snowblower/lawnmower dry.

Thanks in advance!

Do a little search on this site on trex brasilia and see if you want to use that junk. J

Doesn't attaching material directly to the joists under the deck prevent air flow and expedite the rotting of them? How much gap is needed to vent the joists?

I'm about to do the exact same thing with my deck-rebuilding project.

Went to Lowe's to see what's new in corrugated materials. In addition to the old El Cheapo 5-ounce fiberglass everyone's seen on hothouses, etc., Lowe's now offers a corrugated PVC material called "Deck Drain" by the manufacturer. It's around $20 for a 26" by 12-foot piece. And if that's not fancy enough, they also have it in polycarbonate (like what your DVDs are made out of).

One advantage of this approach is that you can build the deck dead level and just shim/furr out the plastic underneath to get the required drainage slope. You'll probably have to use furring strips anyway as the rib spacing on the plastic might not correspond to the joist spacing you're attaching it to. The furring helps with the overall ventilation too.

You'll have to fake it between the deck edge and the ledger beam that supports the joists at that end. You can either just custom-fit the plastic between each pair of joists, or use a flexible membrane between the joists to back-drain over to the main drainage plastic. (I've seen complete systems done this way. They have a funky visual appearance.)

I looked at the "Deck Drain" on their website. I don't know. It seems to me that sealing gaps between deck boards or restricting air flow through is a recipe for a remodel. Even with treated wood. I was working at an old guys house a few weeks ago and he was removing his 12 year-old deck (his words) and those joists were rotted. He used a similar setup.

If you use furring strips perpendicular to the joists to space down and slope the Deck Drain from the joists an inch or so, I don't see how the airflow would be very restricted -- still a lot better than, say, a low deck with sleeper joists.

That's true. I was referring to the "over the joist under the deck board" method. It seals the gaps between deck boards restricting the air flow.

any updates on this? I have been planning on using metal roofing (upside down) to create a "dry" space below my deck where we have a stone patio. I was going to install a gutter system along the outside of the deck and then install the roofing to the joists. I was going to attach a 2x4 to each joist to create a minor slope so the water would fall. I was afraid to use "shims" as I figured they would rot quickly. Just wanted to see if anyone had positive results using a similar method or am I getting myself into a nightmare?

I've done the metal roofing under decks quite a few times. I would suggest using larger boards beside the joist to create your slope, unless it's a really short span 2x4's won't do. Then you'll need to strip those new ceiling joist with 1x4's or 2x4's 24" o.c. @ 90 degrees to the joist. Now install flashing at house then you are ready to screw on the metal roofing. You may need custom flashing around post done at a metal fabricating shop, depending on how you set it up. Use a good grade of metal roofing that has a 1 1/2" ridges instead of the stuff with 3/4" ridges, less chance of leaves creating a dam. Skirt the sides of the deck for a nice finished look. Done right it will last as long as your deck does.