Water behind metal siding over bay window

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Old 06-19-19, 05:20 PM
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Water behind metal siding over bay window

Hi, I have a bay window over my garage and have noticed leaks on the drywall in the garage below the bay window. I confirmed that water is getting behind the siding by spraying the siding above the bay window and observing water draining from behind the siding where it meets the shingled roof of the garage. In the detail below, at each top corner of the bay window, there appears to be j-channels going around the siding above the bay window. A glob of caulking was applied where the j-channel terminates.

Is this the correct way to terminate the j-channel? What, if anything, can I do to stop water ingress?

Thank you,
Peter
 
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Old 06-19-19, 05:34 PM
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Welcome Peter, i see this is your first post.

Number one, steel, aluminum and vinyl siding are NOT waterproof... they are not designed to keep water out. So there should not be ANY caulk at the end of the j-channel. These types of siding require a WRB be installed behind the siding- when the WRB (your housewrap) is installed correctly, there should not be any way the water should leak onto the sheathing or into the wall, as it should harmlessly drain out the bottom of the siding at some point.

Since you say it is leaking, my guess would be that something was done backward and the water coming off the j-channel is getting behind the WRB... or maybe there isn't even any WRB there in the first place!

Only way to find out on metal siding is to remove all the siding (starting at the peak) and work your way down, pulling the nails as you go (without damaging the siding), numbering the siding as you remove it so that you can put it back exactly where it used to be.

A more likely place for the leak to show up would be where your shingle wall flashing meets the house. Those flashing are often installed on TOP of the WRB when in reality, they need to be BEHIND the WRB if you don't expect them to leak. Because like I said earlier, it's normal for water to get behind the siding.

So you might be spraying the top corner but the leak- and solution- could possibly be at the wall flashing above the shingles. Flashing details are quite often done wrong when things aren't done in the right order.
 
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Old 06-19-19, 06:31 PM
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Thank you for your reply. I'm aware that siding isn't waterproof. However, the amount of water entering behind the siding seems excessive in my case. I'm wondering if somehow terminating the j-channel differently (some sort of kick out?) would minimize the amount of water ingress.
 
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Old 06-19-19, 06:44 PM
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Possibly, but there is no way to do that properly without removing siding. And you are still fixating on that top corner as being the point of entry when the siding and j-channel to the left and right of the window (behind the shutters) are just as likely to let water in. You sprayed water on the top corner but where was all that water runoff going... down the side of the window, that's where.

If you wanted to try and make a kickout without removing siding, I would suggest you make an angled cut with a multitool or angle grinder (perpendicular to the roof and flashing) that starts in the center of that blob of caulking, and heads up and left. You would want to make a slot that is about 1/4" - 1/2" wide and maybe 2 1/2" high. That would enable you to slip an L flashing behind the existing j-channel (it's going to hit a nail when you try and slide it under) and out on top of the siding. The back side of your L flashing would then be caulked to seal up the slot, if your goal is to try to keep water out.

My guess is if you did all that and sprayed it again it would still leak. (From the side behind the shutters.)
 
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Old 06-20-19, 05:40 PM
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Great, thank you for the suggestion. I'll try it and report back.

Peter
 
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