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Question DetailsAsked on 1/24/2016

how to fix water coming under or over my j channel when we enclosed our porch

We enclosed our concrete porch. The siding doesn't come to the edge of the concrete. There is about 3 inches in front. So after all said and done we have leaks. My thoughts are the water is coming in the j channel and over it or under the j channel and leaking into the inside. So now how do we fix this. My only thought is that we use flashing that will hang over the end of the concrete and up behind the j channel. We have to tear off the siding. So any better thoughts or ideas. But a question. What would of been the right way to do this In the first place. Did we do it wrong. Thanks

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Not totally clear on your situation - sounds like you enclosed the porch and built back from the front edge o the slab so the wall does not sit on the edge, and the siding does not hang down over the front of the porch slab as it usually would - VERY unusual to do it that way, and would require significant flashing effort to make it work unless the front edge ofthe slab sloped significantly away from the house, in which case some caulking and base L flashing driven in under the bottom plate of the wall might work.

And why a J channel was used - not clear there either, unless you were trying to use that as a bottom-of-wall gutter ? But it would not have the slope to act as that, so just sounds like a dirt and water trap.

You likely have two problems - trapping of the water from the siding in the J channel, and water coming under the J channel or under the sill plate along the top of the concrete. And a third issue - if the wall was not built with heavily treated bottom sill or plate (the bottom horizontal 2x4 or 2x6 that the studs are fastened to and sits on top of the concrete - or perhaps a bottom treated sill plate under the wall plate - that is likely to rot quickly too.

Best solution I see - removing bottom of siding, treating the bottom plate/sill plate with copper treatment like Cupreanol (watching out for penetration as it will stain concrete badly and pretty much irreversibly), caulking along the sill plate/concrete interface with high-grade 30 year caulk, then putting on an apron or Z flashing like is used on decks - see images below. Then put the siding back over the Z flashing.

You definitely need GALVANIZED flashing (or the more expensive stainless or copper), in my opinion (which can be pre- or post-painted as you wish), because this is going to have water and maybe snow sitting in it a lot over the years. The flashing has to go up behind not only the siding but also behind the the water barrier in the wall, and should go WELL up the wall - I would use probably a 6x3x3 flashing (or at least 4x3x4) or apron flashing if the space in front is 3 inches or less - or you may have to have flashing specially bent for the job (not a big deal to have that done). (4 to 6 inch leg up into the wall).

Where the diagrams below show the flashing above a deck ledger board, just imagine that is your concrete face. Typical installation details below, FYI - (bottom image)

Note that the lap joints (2 inch minimum lap, I would recommend 4 inch) on the pieces of flashing should be liberally caulked and, at the exposed sections in front of the wall, should be fastened mechanically - I predrill and use aluminum pop rivets at about 2 inch spacing, sealing the hole in the pop rivet afterwards with long-life caulk, paint touchup as desired. Of course if using copper, then solder. I also rivet the overlap at the bottom of the Z, so the exposed end corners do not become a snagging hazard to people walking by. And of course, the longer the pieces of flashing, the fewer the number of seams to potentially leak.

Also, the "horizontal" or middle part of the flashing should slope significantly downward as an apron to ensure drainage (so apron flashing will be easier to use than Z flashing if you can find it with wide enough center section), so you may need to shim under the back edge on top of the concrete to provide a uniform slope - or depending on where your J channel is, maybe that can serve as the back support/guide. If wood is used for shimming I would use cedar or treated wood. Slope like this flashing designed for use under lap siding -

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I would ensure that some airspace is left to the area under the flashing, but with bug screening to keep it from becoming a bug haven - will take a bit of creativity - perhaps multiple folds of screening along the front edge of the concrete with the flashing in tight contact, so air can exchange. The flashing needs to protect the base of the wall and prevent blow-under as well as run off water coming off the siding or falling on the porch slab projection.

Not knowing where the J channel is and what it is doing, I can't comment much on that - but sounds like it needs to come out entirely if under the bottom of the siding - that is not a place for that product to be used.

Answered 3 years ago by LCD

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