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Window caulking question

kevinjm4 | Posted in General Questions on

if it is relevant I have a rain screen assembly, w/ 3/4” thick plywood as my furring strips w/ Tyvek house wrap. And this is probably relevant too – I did make a way for the rain screen to vent out at the bottom of the window

On the vertical portion of the right side of the window, what you see there in one of the pictures is what jeldwen calls a mull groove filler, it’s a strip of vinyl that snaps into the groove that runs all the way around the window. Presumably this makes it easy to attach jeldwen custom trim; just snaps in place. My dilemma is this – do I even use those mill groove fillers, do I caulk the groove instead… of I don’t caulk but opt for the groove filler this is time consuming (not easy to install) and doesn’t seem waterproof anyways)  and I’m asking because without anything filling that groove, as you can see there’s almost no ‘meat’ for the caulk to stick to.

the bottom horizontal portion of the window does not have anything installed in the groove as you can see, as it would cover the week hole, I tried installing a strip while drilling a hole wherever the weep hole was, and it just didn’t drain that well as it gets trapped behind the mill groove filler strip.

a) what should I do with the vertical joints?
b) what should be done about the weep hole/bottom joint?and is caulking the bottom of window trim even necessary or not ideal at all given the venting provided already? The trim is flat at the base of the window for about 1”  and then slopes down – I will try and include a good picture of this.

and sorry for any sideways pictures – some seemed right others were sideways and I couldn’t fix…

thanks for any help.

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  1. Expert Member
    Akos | | #1

    You can go either way. The budget windows I get don't come with any fillter, I either caulk right over the groove or put metal flashing into the groove as needed.

    You never block weep holes as you can end up with your window frame filling with condensate. Caulk across the bottom but leave a gap where the holes are.

  2. kevinjm4 | | #2

    I’d probably feel more comfortable caulking rather than flashing here. So basically with these types of windows it’s just going to take a little more caulk... I’m thinking I will fill and smooth the groove - then I’m basically working w/ a normal window at that point. Caulk edge of window to edge of trim, leave top alone let metal flashing do its thing, and bottom don’t block weep holes.

    Just one thing maybe you didn’t notice but what about how I do have my rain screen able to vent right there - should I not caulk the bottom for this reason?

    1. Expert Member
      MALCOLM TAYLOR | | #3


      The main goal of a rain-screen, or any other cladding, is to prevent bulk-water intrusion, so that definitely takes priority over venting the cavity.

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