Building a Weatherproof Deck

[bobdoo]

I am wondering how others have covered their decks to provide a dry area underneath. I have built a deck structure 16' x 32' attached to 2nd floor level of the house by a 2" x 10" ledger board bolted on. House siding is Hardiboard cement board so flashing will have to be caulked/fastened to outside surface of siding. Have approved building permit and design meets FL Building code. Deck area is joists on 16" centers covered with 5/8" OSB which is covered with waterproof leak barrier material (GAF Weather Watch Grandular Mineral Surfaced Leak Barrier). I have enough 12" x 16' PVC hollow core deck boards (manufacturer u/k-see atch photo) and stainless screws to cover the deck but have reservations about water getting under the deck boards and causing problems, ie. mold, etc, and expansion problems. I am thinking of using grooved 2" x 6" PT boards around the perimeter to cover the hollow core (to keep out pests) and to provide finish to sides and ends of deck boards. Location is Florida coastal area. I would appreciate any comments, suggestions or criticism of this project.

[Winchester]

How much is the deck sloped?

The grooves will be vertical for drainage around the perimeter?

Never heard of the products. Are you screwing through your waterproof membrane? Does it seal penetrations?

[bobdoo]

Winchester,
Thanks for your questions which I did not address in my initial description. The deck surface has a very small slope - 4" in 16' (1/4" per foot) and the grooves between the deck boards will be in the vertical position for drainage, however I'm still considering using 2" x 6" PT lumber around the perimeter to cover the end openings in the PVC deck boards and on the side edges to cover the PVC flanges (see photo). Yes, I am planning to screw the PVC deck boards thru the flush flange to the deck structure (thru the asphaltic membrane into the 5/8" OSB/joists). The membrane will seal the screw penetrations. This membrane can be used in lieu of roofing felt under regular asphalt/fiberglass roofing shingles and satisfies the FL Building Code, but I am not using shingles, but rather, the PVC deck boards. I have not applied the deck boards yet and wanted to get opinions/suggestions from the experienced decking builders/contractors on this forum before I proceed. Also, do I have to be concerned about thermal expansion of the PVC deck boards across both the width (32 ft) and the length (16 ft) as the temperature extremes will be from a winter low of 28F to 105F summer temps?

[Winchester]

I don't really use PVC for anything but the occasional exterior trim. So take my advice with a grain of salt ;)

However, yes, thermal expansion is probably something you should consider in your design as PVC is known for that. Since your decking looks rather hollow it might not be much of a concern across the width. It should be something you talk to the manufacturer about as they "should" know their product best.

As far as membrane satisfying code under a shingled roof. Generally the requirements are different for a sloped roof vs. a low sloped roof vs. a flat roof (which is what your deck is).

For a flat roof, penetrations are much more of a concern/issue and should be minimized whenever possible. If it is not too late, I would consider using sleepers over the membrane and screwing the decking to those.

As for the PT 2x6 perimeter, find out if the manufacturer recommends expansion joints and go from there.

If there is a manufacturers warranty you don't want to void it, so find out everything you need to know from them regarding installation requirements.

[Bayn Wood]

That would turn out really bad ...!!! Ice and water shield is not for that purpose, it is for roofs with at least a 3/12 pitch. If you going to do it that way use 3/4 treated plywood cause it is going to get wet!

That decking is going to move as much if not more than vinyl siding, and you know what they say about vinyl siding don't nail it tight because it will buckle, now imagine that plus a wet sub-floor....yikes

The only similar application I have seen is this - http://www.wahoodecks.com/dryjoist/ I have no idea if the product is any good we have never used it. They also have a aluminum tongue and groove decking that is suppose to seal the water out and down the groove/gutter portion of the decking.

Timber Tech has a good under deck drainage system we have used before http://www.timbertech.com/products/finishing-touches/dryspace-drainage-system/default.aspx

Trex also has a good under deck prodct we have used before - http://trexrainescape.com/

Hope that helps