I recently moved homes. I am getting a pretty bad leak above a window. I assumed it was the flashing, but before I even got that far I noticed the J Channel looks very wrong (to my amateur eyes).

There is a large gap in this image taken from above. First of all, I wanted to get confirmation this is incorrect. Secondly, if so, what is the best solution?

I checked a few other windows and now I am pretty sure all 20+ of my windows have this gap in the J Channel.

gap between J channel

Edit: Below is a picture of the window under the siding. Would the flashing be under the black stuff? Or does this mean there is no flashing? If none, does anyone have a go-to how-to video or it is easy to DIY?

window frame under siding

Edit 2: I used a water bottle to dump a few liters of water over the J channel. No leak. I decided to go up to the next weak point, a bathroom vent. I poured 1 liter of water all around it and it leaked! I freed the piece of siding under the vent (see pictures below). The water seems to be going behind the black stuff.

  1. Is there a quick fix to prevent further leakage?
  2. What is a good permanent solution?

bathroom vent

partial under bathroom vent

under bathroom vent

under bathroom vent different view

  • Yes that is wrong. The upper piece should have an ear overlap to direct water away, but even with this, the window should be flashed and it probably is not. You'll have to give us a few more pictures, and expose the area around the window to get more info
    – noybman
    Jul 19 '19 at 0:28
  • Sure I’ll disengage some siding and try to get a better look.
    – rys
    Jul 19 '19 at 2:13
  • @noybman I added a picture of the window under the siding.
    – rys
    Jul 20 '19 at 4:03
  • that is peculiar - the window is a vinyl frame, this makes me think the water getting in has nothing to do with the junk job on the J-Channel, even though it is a junk job. It may be getting in from higher up. I don't see 'tyveck' (house wrap), and the window has a natural lip, but water can be getting in from walking the wall. Can we get one more photo of the wall in question
    – noybman
    Jul 20 '19 at 4:13
  • 1
    Thanks @noybman I added even more pictures :)
    – rys
    Jul 20 '19 at 20:58

As Iggy noted his answer is absolutely correct for J-Channel installation. The guidelines he recommends help keep water flowing away-from and down-to the bottom of the house.

Your siding installation from what we can see was not done with a number of typical guidlines in mind. The J-Channel is just one of these. Often times before applying siding, the house surface will be prepped with foamboard to add R-value and flatten the surface, and/or, joints are taped, or housewrap is used. Around windows and doors (very often) an aluminum brake is used, or more felt paper,or additional drip caps or even other pieces of vinyl are used. These things are installed anywhere water can get inside the structure. They are installed to promote water to "stay on the surface" of the wall, and travel down via gravity.

In your case, it looks like none of these things were done. The properly cut J channel is just one step. Looking at your photos you want to release more runs of siding, going up the wall, looking for where water is dropping into the wall. This will be anywhere the siding is cut for protrusions or doors/windows, corners, and lastly, the weep holes of the siding itself.

Your photo shows a dryer vent right above the window. It has a lot of water around it. You show wet area behind the siding. This is probably where the water is coming from. Actually, this and any area above it.

use the tips Iggy provided, but for each of these areas, add flashing, making sure to tuck the piece being added uder tar paper or other flashing above it. Continue thos overlapping process all the way down the wall. Caulk or use great stuff on large gaps and joints before doing so, this is just a good practice.

You can do quite a bit without pulling the siding off completely, but in my opinion, you could at least do this entire wall properly faster by doing it right. (meainging pull it off and do it right), then put it back up. At a glance it looks like this wall sees a lot of weather, if so, this is a good measure to take.

I'm not suggesting you redo the whole house, but at least take the right measures to solve your issue with this wall.

I recommend you examine the slope of the vent pipe shown. Make sure it meets ~1/4" per foot. also, where it protrudes from the house, (and technically the entire run) make sure the seam is up, so water isn't given the chance to drip. At the protrusion, it should extend past the hole so that the water that drips from the end is not allowed to run down the wall. if it is running down the wall, it is kept to the surface via overlaps until it reaches the ground.

  • Thanks again. In my picture there is a gap between the wood. So if i understand correctly I need to caulk that gap, then apply flashing onto that wood directly then over the top of that black paper?
    – rys
    Jul 21 '19 at 2:28
  • To each their own. looking at that gap, its a big one. Can spray foam might be a nice addition, but you must cover it with a layer of housewrap or tar paper. The housewrap is cheap and manageable. Yes, you need to cover it, but make sure the top of your addition is UNDER the layer above it, and OVER the layer under it.
    – noybman
    Jul 21 '19 at 2:38

EDIT, due to new info: Thank you very much for the further investigation! I assumed too much and should've asked if there were any other siding penetrations above.

Anyway yes, a quick and easy fix is to apply a liberal amount of almond color (whatever comes closest) caulk that's fingered or forced into any gap at just the top and sides...so any water gathered at the bottom can still drip out and breath to evaporate.

Don't fill the back of the vent with caulk. Instead use a Foam Backer Rod or even thick weather-stripping to give the caulk something to seal onto. And still, probably do 2 applications of caulk, to make sure the 3-sides are filled and adequately thick.

A proper permanent fix is at the end, but 2 materials in an optional non-removal of the vent is to either install the Drip Cap mentioned below/initially or a piece of Step-Flashing to the top of the vent, which tucks under the siding. Step-Flashing is much more customizable.

Your vent was installed with the row above as an overhang to keep water out. Unfortunately, this only works with correct J-channel picture frames (just like a window) or J-channeled penetration boxes and not with the entirely wrong vent that protrudes as much as the siding itself and has no top and sides flashing flanges.

However, you're lucky. You can just cut the siding's locking lip out of the row above the vent to get the Drip Cap or Step-Flashing flange behind the siding. You still want a tight Z-shape to your flashing, which is why I think the Step-Flashing will work out best with possibly just household scissors. You'd still caulk the sides as a wind precaution, but the top flashing would really do everything needed.

Finally, the best option is to remove the siding and old vent, which seems to be a 1-piece construction. You want a 2-piece construction that has an installation flange where the vent flaps snap onto and holds the siding to the wall...see Instructions/Assembly here, not Installation Guide here for what I'm saying https://www.homedepot.com/p/Builders-Edge-4-in-Hooded-Vent-117-Bright-White-140116774117/100673014

Further, there are also 1-piece penetration boxes that have seamless J-channel built-in (backed picture frame of J-channel to cut your own hole into for whatever accessory), but only roofing and siding suppliers have those and may not sell to an individual...definitely try online or in person though, if it's what you might want.


I do still think you should do the below. As, water may still be running on top of the "black stuff" and will find its way in, if it hasn't started to already.

You are very correct that it's very wrong. Ideally, you should have a Drip Cap under the top J-channel. But, many installers just use the J-channel itself as the Drip Cap, since it's a little more uniform looking and of course faster and cheaper..."experts" cutting corners (literally in your case) because they know what they can get away with.

However, you can correct the inherited problem fairly easily for each window and door within the siding (I put Drip Cap everywhere possible). By, buying Drip Cap and either installing it correctly and pulling the siding panel free for a complete re-do or by cutting the Drip Cap's back off to just slip it under the J-channel.

Either way means you cut a tab into each end of the Drip Cap's bottom back corner, which is then bent down into the side J-channels to direct water harmlessly away from the top corners. Here's a great video demonstrating the proper process of J-channeling, top piece starts at about 12-min. How To Install J Channel (Vinyl Siding) https://www.youtube.com/watch?v=gmiN3BnOu3w

  • Do I need to remove any siding to do this?
    – rys
    Jul 19 '19 at 0:56
  • Only if you want to re-do it like a fresh install...you'd just free (not remove) the panel bottom and brace it out of your way to do your work. Otherwise no, for option 2 you would just be slipping the Drip Cap's remaining bottom slat (after you cut the back of the L-shape off) under the J-channel and then poking its tabs down into the side J-channels (tabs can be just an inch or you can go much more).
    – Iggy
    Jul 19 '19 at 1:45
  • Thanks a lot. I may try option 2. While slipping it under the J channel does it need to be secured to the J channel by some kind of adhesive or will it stay on its own due to the tabs and/or by leaving a bit of a lip from the L in place? Also, not even sure if this is the root cause of the leak :( but plan on fixing them all just in case
    – rys
    Jul 19 '19 at 2:12
  • Yep, the tabs and J=channel friction will hold it. But, if you have room for a bit of L, then that or a thin bead of caulk would only help.
    – Iggy
    Jul 19 '19 at 2:16
  • 1
    Thank you and I totally agree, as fully displayed with the new and 2nd picture and only slightly revealed in the 1st pic. But, this is just phase-1 and plan-A. The house is a very typical garbage job where the siding is the only waterproofing of any openings. While absolutely terrible it does work if the siding is done right. If, this fixes the cause for water intrusion then well enough and an air-leaky house won't rot around them.
    – Iggy
    Jul 20 '19 at 11:33

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