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Repairing Window Exterior Molding - grwold - 04-29-2025
I recently noticed some serious rot in the molding on a rear window.
[attachment=54480]
This window is only four years old, having been installed during a kitchen remodel. Apparently my contractor took a shortcut in wrapping the vinyl edging around the wooden molding, allowing water in.
[attachment=54481] [attachment=54482]
(both views from above, looking down the side of the window)
I will cut the rotted molding out to replace it, but am wondering what I can do to prevent water from impinging in the future. Lots of silicone caulk seems like a poor solution, both design-wise and for effectiveness. Maybe run a 1" eave, vinyl, tin or copper, across the top of the window? The current vinyl edging isn't just short on that left end, it's also composed of two pieces jointed together in the middle of the top run.
[attachment=54483]
Lastly, should I replace the one piece of molding with wood, or is there a better material to use, with which I should re-do all four sides?
[attachment=54484]
Greg
RE: Repairing Window Exterior Molding - jteneyck - 04-29-2025
I'm no pro at this, but I believe you need to use a Z shaped piece of flashing that goes up under the shingle and then over the top edge of the window molding. The vinyl trim goes over that. As for the molding itself, I'd replace it all with AZEK. Once you get the molding off, you should find a water barrier. If not, more trouble to deal with while you're at it.
AZEK and other PVC products will never rot. You can pre-make the molding as a unit, with glued corners, then install it as a unit. You can paint it with any vinyl safe color you want.
RE: Repairing Window Exterior Molding - grwold - 04-29-2025
(04-29-2025, 10:08 AM)jteneyck Wrote: I'm no pro at this, but I believe you need to use a Z shaped piece of flashing that goes up under the shingle and then over the top edge of the window molding. The vinyl trim goes over that. As for the molding itself, I'd replace it all with AZEK. Once you get the molding off, you should find a water barrier. If not, more trouble to deal with while you're at it.
AZEK and other PVC products will never rot. You can pre-make the molding as a unit, with glued corners, then install it as a unit. You can paint it with any vinyl safe color you want.
Thanks, John. Azek seems pretty common around here, and the big box stores all have the z flashing/z cap (is it odd that a local building supply store does not carry that?). Assuming there's a water barrier behind the existing molding, this ought to be relatively easy.
I appreciate the help!
RE: Repairing Window Exterior Molding - jteneyck - 04-30-2025
(04-29-2025, 07:54 PM)grwold Wrote: Thanks, John. Azek seems pretty common around here, and the big box stores all have the z flashing/z cap (is it odd that a local building supply store does not carry that?). Assuming there's a water barrier behind the existing molding, this ought to be relatively easy.
I appreciate the help!
Yeah, the place where I bought the vinyl siding from for my shed, a huge volume place, didn't sell those Z flashing pieces either. Strange indeed.
John
RE: Repairing Window Exterior Molding - EightFingers - 05-01-2025
What did the contractor say? Did you show him the picture?
RE: Repairing Window Exterior Molding - grwold - 05-01-2025
(05-01-2025, 11:06 AM)EightFingers Wrote: What did the contractor say? Did you show him the picture?
That's a long story. This is the latest in a series of issues with the guy's work.
The whole situation is sad, as he'd done a couple of good jobs for us before we brought him in for the kitchen. We still comment on the change in his work ethic & quality. We wonder and hope he's over whatever the cause was, but we are not in touch with him any longer.
RE: Repairing Window Exterior Molding - MstrCarpenter - 05-02-2025
(04-29-2025, 10:08 AM)jteneyck Wrote: I'm no pro at this, but I believe you need to use a Z shaped piece of flashing that goes up under the shingle and then over the top edge of the window molding. The vinyl trim goes over that. As for the molding itself, I'd replace it all with AZEK. Once you get the molding off, you should find a water barrier. If not, more trouble to deal with while you're at it.
AZEK and other PVC products will never rot. You can pre-make the molding as a unit, with glued corners, then install it as a unit. You can paint it with any vinyl safe color you want.
Yea, earlier this week I had to deal with rot under vinyl siding. The trim was wrapped with aluminum coil and it looked o.k. from a short distance but the installer relied on caulk to keep water out. (and not silicone or Butyl). The window sills were in a pool created by the alum. wrap, and the sheathing and framing were rotted to the foundation. The carpenter ants loved it.
You should have window flashing (the "Z" flashing) on top of the casing set in silicone or rubber caulk, flashing tape over the "Z" flashing to the sheathing, and the house wrap extending down over the flashing tape, and that can also be flash taped to the 1st layer of tape for good measure.
Ideally, the "Z" flashing should be left about 1/4" long on both ends so it can be bent down over the ends of the head casing. If you don't want to replace the casing again, I would skip the miters and use butt joints. The important detail is that the top of the side casings are beveled about 20° up under/behind the top casing and pushed into a bead of caulk so water won't wick into the seam. (The caulk isn't really to keep water out of the joint forever; it's to seal the open end grain pores so it doesn't suck water in.)
RE: Repairing Window Exterior Molding - Snipe Hunter - 05-03-2025
IMHO, there's only one right answer. Take off the siding and J-Channel and re-install it correctly. You'll have to get more J-Channel. I don't know why people still use wood trim. You might be able to install the new J without pulling the siding but it's usually more of a pain than removing and re-installing the siding. I'd check all the windows. Like said above, I don't see any Z flashing either so my guess is it wasn't flashed correctly either. I'd definitely be on the phone with the contractor. That's a botch job
RE: Repairing Window Exterior Molding - MstrCarpenter - 05-04-2025
That siding comes off from the very top down; a hook tool is useless on it. To replace a piece in a field it has to be cut in half lengthwise. To replace, there are teardrop shaped "repair clips" that get pulled down with monofiliment line which are then cut off.
On a repair like this, the "J" channel would be secured to the sides of the casing with 1/2" -3/4" #4 or #6 S.S. pan head tapping screws. There's enough room just under the bottom of courses for long driver bits. It's plural because I stab the screws through the sticky side of electrical tape then tape them onto the bits. Magnets don't play with stainless steel screws well and it's easier to swap tips than tape the screws on up on a ladder.
RE: Repairing Window Exterior Molding - grwold - 05-13-2025
So it's taken a bit, but I've identified the siding (which was on the house when I bought it) as CertainTeed Cedar Impressions D7 Straight Edge Perfection, in Forest color. CertainTeed's installation guide shows using J channel, including trimming & wrapping for rain, but does not mention Z flashing. Based on the other windows, the original installer didn't use Z flashing either. Is Z flashing, then, extra security, or should I trust CT?
I'll probably buy a half square of siding and new J channel. Among other things, the contractor who did this said, then, that our siding had been discontinued and he "got the last two boxes on the East coast." But still, it wasn't enough to do that wall with the new window, as there are places where the sheets butt against each other, some with clear caulk as a (now failed) sealant, rather than overlapping. So, a strip & re-install of the siding seems necessary.
Thanks to all for your input, especially Snipe & MstrCarpenter.