Vinyl J channel used at bottom holds water

Submitted by Ray Thornburg on Wed, 09/26/2012 - 08:30

When Vinyl J channel is used at the Bottom

Have you ever seen vinyl j channel used at the bottom of a wall and wondered what happens to the moisture trapped by the channel. Probably not..... that's what home inspectors are for... right. I see this problem more than I should even on new homes. Let's take a look at a pretty picture to start our discussion.


how vinyl j channel can hold water

    In this photo you can see how water flowing down the wall will be caught in the j channel where it will flow sideways until it finds an exit path. If the corner in this picture is not flashed correctly from underneath the J channel then moisture might penetrate the structure.



Actually the proper way to start horizontal vinyl is to use a metal starter strip. In this way no J is used.  However;  to use a starter strip you have to start with a whole piece.  Sometimes this isn't possible because installers want to line the siding up to be even with other siding for aesthetic purposes or because the siding is being ran vertically. 


inside view of vinyl j channel

    Here is the inside view of the vinyl j channel. You can see how water can be funneled sideways in this picture.





vinyl j channel holds water

    In this photo you can see an actual home where moisture damage is occurring. Water was being diverted to the door where it was being absorbed by the building materials. Inside trim and sheetrock and door jambs were moisture damaged. Not knowing the real reason for the moisture damage might make someone spend more money on ineffective remedies like replacing the door or adding a storm door for example. I happen to know that in this case another inspector had failed to advise his client about this installation deficiency. In this case using J channel at the bottom was unnecessary because they started with a whole piece which means they could have used starter strip instead.

The Solution

When vinyl J channel is used at the bottom like this proper flashing is essential especially at the corners. Also; 1/4 inch weep holes should be drilled about 12 inches apart into the J channel only. This will help keep the track dry and prevent accumulation of unwanted moisture. Siding manufactures differ in their recommendations regarding the spacing of the holes and the size. Page 28 of the Vinyl Siding Institute's installation manual is one such manual. Another is page 24 of the KP building products manual.

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Submitted by Ray Thornburg on Wed, 09/26/2012 - 08:30


Anonymous | Sun, 10/08/2023 - 22:42

Very true everyone has different installs on J channel with Board & Batten vinyl, even weeps on top J under soffit. Sider installed bottom J with weeps ontop of alum flashing that wrapped 2 stacked 2x4s. He couldn't raise the bottom J channel due to furring behind 1" raised insulation, kept above standimg water. I worry J, even with weep holes, won't drain & cause suction on aluminum wrapped studs. Should J at top of B&B also have weep holes? What are your thoughts?

Ray Thornburg | Fri, 10/13/2023 - 18:20

Should J at top of B&B have weep holes? That's hard to answer without seeing it. Mostly I would say if you look carefully you'll see how the water will flow. If it's high under the soffit then it's unlikely to receive any direct rain, but if it's somewhere rain falls it's a possiblity. Mostly it's an issue if flashing is not applied at the right locations. As long as flashing is applied where it's needed and the water has somewhere to go (weep out) it's ok. Hope this helps....

Anonymous | Wed, 06/03/2015 - 06:22

Ray you are spot on. We had vinyl siding installed on our second story. Our siding installer used J channels at the bottom of the siding where it interfaced with the first story roof and other areas. Upon recent persona inspection I observed and concluded that was not good as the channel acts as a dirt, debris and water trap. I carefully poured a little water in the channel and it was still there as of today, June 3. 2015, 48 hrs. later. Can the channel be dremel cut so the outer channel wall is totally removed so as to prevent debris collection as well as water drainage? Weep holes in that same wall would allow water to escape but debris would still accumulate. Also snow would be another source of moisture here in Cincinnati Ohio. I was going to hire a local house inspector who is experience in vinyl siding matters as we hope to sell the house soon. The low country is one of our top choices for downsizing and retirement living. I have a Summerville realty sending me email updates regarding listings in the area. Thanks for the manual links in your article. George Spite 513-919-2648

Ray Thornburg | Wed, 06/03/2015 - 16:17

Mr. Spite:

Thank You for reading my article. You should not totally remove the outer j channel as it acts to hold the siding in place. Weep holes are the way to go if you are having problems. Of course if you are having moisture penetration consider adding some flashing behind the j channel where it needs it. Most of the time the water drains out where the pieces are put together but occasionally it'll drain sideways where it'll cause moisture issues. Hope this helps.....

Anonymous | Sat, 04/27/2019 - 03:40

I just had to complete a $12,000 repair that included a rotted rim joist due partly to a J channel used around the bottom of my siding. According to my contractor my siding is no longer available, so getting a starter strip installed is not possible. I have drilled weep holes recommend by my inspector, but what are your thoughts about blocking water exit with caulk at the ends of the channel where the flashing will also end?

Ray Thornburg | Sun, 04/28/2019 - 19:58

Thank you for your question....unless your vinyl is unusual...another brands of starter strip may work. It goes behind the siding so you can't see it. If it is flashed correctly you shouldn't need the caulk...Sealants are never really considered a permanent solution but if all else is correct I guess it can't hurt. The use of sealants in unusual locations make it look like you had a problem but didn't fix it right. Remember though that some sealants don't stick to vinyl good enough to keep out water so it could just be a waste of time depending on the type of sealant used. Quad is good and sticks to brick, vinyl, metal and is elastomeric....but it is messy so be careful. The bead can't be smoothed out with your finger easily for instance. A sealant like this is often used at window to brick locations so as to allow for expansion, contraction of brick at those locations. Hope this helps....