I have a 14'x25' space under my screened in covered porch (look-out elevation), that I would like to create a dry storage space. I have read online forums on how to install a corrugated roofing system underneath the joists at a pitch and install gutter irrigation. However, I'm not sure how to make it water tight, given I have many 6x6 posts that get in the way during my roofing installation. Additionally, I would like to run the gutters at a pitch away from the house (first photo), however not sure how I can ensure my walls up to the posts will remain water tight without some flashing (or something to keep the water out beyond the roofing material). Is there a good solution to wrap the 6x6 to allow drainage onto the roofing material? The ideal solution is to build walls up to the existing posts, wrap them, put siding on and install a barn door on the exterior (leaving an area around the window open for fire exit). I just got concrete poured, so looking for any help on next steps.

 

It looks like you have a roof over the 2nd story deck so installing anything under the deck isnt really going to do much more for the fist floor area!

Doesn't it stay dry currently?

 

It mostly stays dry, but rain doesn't always fall straight down, and I want the below area to be water tight, so I can use the space as a shed.

 

That looks like an egress sized window underneath the porch? Is there a bedroom in that corner? Enclosing the area under the porch can render it useless and void it's classification for egress and could mean that that room can no longer be a bedroom.

 

I don't plan to enclose in front of the window, as I do plan to retain the bedroom in the basement.

 

I misunderstood. I thought you were enclosing the space. If just adding a water collection system the bedroom egress window shouldn't be affected.

I've seen a couple systems similar to what you're considering. Most, just go up to the posts and fit as close as the installer's skill with no water sealing. What water hits the column remains stuck to the column and just runs down and out along the floor.

I have seen a few where they did try sealing to the posts. One made shallow saw cuts in the column and inserted flashing much like you'd flash a chimney/roof intersection. It looked like it worked but I'm not going to advise anyone to make saw cuts in their structural column. I might consider it with 6x6 posts but a 4x4 post is actually 3 1/2 x 3 1/2" (at best). If you make a 1/2" deep cut all the way around the perimeter you're down to only a 2 1/2" square of wood carrying the load.

Another installation I've seen used a flashing tape. Aluminum on one side of the tape and a thick bitumen/tar like adhesive on the other. It had been up for a couple years and still seemed to be sealed pretty well. Since your posts are aged, dry and painted I think you'd have good adhesion as long as the paint is well stuck to the wood.

 

Not really sure what you are envisioning. IMO, just putting 4ft of pitched roof around/under the perimeter of the deck would probably take care of 99.9% of the rain, and would be easiest to accomplish. Your blocking kind of prevents you from using any product that gets pitched toward the front since those products go up in the joists and are pitched to the front.

if you would be satisfied with 4 feet of perimeter protection, frame up your perimeter walls about 6.5 ft high... Use 5 ft rafters that would sit on the perimeter walls then run them up alongside your joists. Sheet it with plywood (outside corners will be hip roof corners) then put hi temp ice and water on it. Fold the ice and water up on your posts to flash them. Run it up about 6" and cap it with a terminator bar, Geocel or Solarseal roof sealant on the top of that bar.

Then put some metal roof panels on top of that. Use foam closure between your gutter apron and the bottom of your roof panels.

Typically if you want a 100% dry area under the deck it has to be planned from the beginning, before any decking even goes on.

 

Xsleeper's suggestion sounds good but a lot of work and probably not the best looking solution. Depending upon what and how much you plan to store, a couple of free-standing storage sheds might work, may look better and can be moved or removed easily. Get an extra for the kids to use as a play house.