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Community and Q&A

Drip Cap for New Windows

gtmsmith | Posted in General Questions on

Hey GBA – Looking for some advice here…

31 Year old home
2×4 construction
1×8 channel rustic cedar siding
S.E. PA 19382

I am replacing the siding and windows on two sides of the house and have a drip cap/trim question…

My existing windows are not trimmed. The siding is diagonal (I know, its terrible) and the siding goes right up to the edge of the window. The drip cap (can I even call it that its so small and tight to the window?) is on top of the window since there is no trim.

My new windows are Andersen 400 casement double pane and they have a continuous hydro formed vinyl exterior. These new windows will be trimmed with cedar. I think it will look nicer and it will allow me to match windows in the future where I wont be taking all the siding down. The distance or depth from the nailing fin to the outside of the frame of the window is 1.313″. I will be trimming the window with 5/4 x 6 cedar ripped in half (so the board will be 2.875″ wide and 1.063″ thick)

This then means the window vinyl frame will stick out from the trim 0.250″ and that will be a little ‘ledge’.

And the trim extends out from my siding 0.438″.

So the question; Do I put the drip cap on the window? Or the trim? Or both?

I have found zero examples of this online in all of my research. It seems most times when someone is trimming around a window the trim is the same thickness as the depth or amount of window sticking out… so they put the drip cap atop the trim of course…

Does my concern or question even make sense?

Thanks for you help!



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  1. Expert Member


    If the trim around the windows goes back to the sheathing, the head-flashing needs to go above the trim. If the trim is applied to the siding afterwards, the flashing goes on the window.

    A good installation includes bedding the flashing in a bead of caulking, and end-dams on the flashing.

  2. gtmsmith | | #2

    I will have end dams on my drip edge and be back caulking for sure.

    The wall will be bare, I will not apply the trim overtop of the siding. The trim will go on top of the WRB and the flexible flashing around the window and then I will install the siding up to the trim.

    So the window will stick out about 0.250" though still further than the trim... and you are saying that is 'ok'?

    I suppose I could always build the trim out even further so it is line-to-line with the outside of the window...

  3. Expert Member


    The ideal situation is that the trim is proud of the window so you can caulk the joint between the two, and the head trim (with its head-flashing) protects the top of the window.

    Most window manufacturers here have 1" to 1 1/4" of frame outside the flange, meaning 2"x trim works well.

    1. gtmsmith | | #7

      Certainly, that is why I am confused. I have always seen the trim proud but these windows extend from the nailing fin a bit more than what I have seen.

      Never seen 2" thick cedar trim...

  4. Expert Member
    Peter Engle | | #4

    The Andersen Series 400 windows are essentially self-flashing because of the continuous molded nailing fin. If you properly tape the fins to the WRB, no additional head flashing is required for the windows. Follow the Andersen installation specs diligently. The wood trim should have a head flashing above it, per code: "Flashings shall be installed above all projecting wood trim..."

    1. Patrick_OSullivan | | #5

      Peter, that's an interesting thought. Do you think there's not much benefit to adding a drip cap on trim for windows that fall into the category described? (Assume the trim is a composite, not wood.)

      1. Expert Member
        MALCOLM TAYLOR | | #6


        Head-flashing becomes more important with rain-screen cavities, but I take your point. Why isn't the head of a flanged window formed with end-dams and a protruding extrusion that mimics the shape of the head-flashing we have to apply separately?

    2. gtmsmith | | #8

      The andersen instructions actually show a drip cap on the window and not the trim

      ill try and attach here

      note 18 on the instructions show the drip cap on the window, then they show the trim and make no mention of a drip cap in the trim

      so confused!

      1. Expert Member
        MALCOLM TAYLOR | | #9


        That makes sense. Anderson are interested in protecting the windows. The drip-cap above the trim is part of the wall assembly - like any other piece of trim - not part of the window installation. If Anderson wants flashing over their window heads, I'd do that. You still need a way to stop water getting in between the trim and siding above. So it looks like two pieces are necessary.

        1. Expert Member
          Peter Engle | | #10

          Yep, I was wrong. Andersen changed their installation instructions again. They definitely do require a drip cap above the window now. They used to consider the flashing tape to be the required "flashing" but not any more. If the trim is composite, I think technically a drip cap is not required above the trim, but it wouldn't hurt. If wood trim, a drip cap is required by code.

  5. gtmsmith | | #11

    Good point... I like the idea of composite trim and only needing a lick of paint every 5ish years or more but with the entire house being cedar, and a wooded lot, I wanted to keep some of the natural charm

  6. gtmsmith | | #12

    It was just suggested to me today that I could use Boral material as my window trim...

    put the drip cap over the window like Andersen says and then trim around the window with boral, and not put a drip cap on the Boral, but rip it at a slight angle for the top portion to drain a bit and then seal/caulk the edges. Seems to make sense to me...

    Also, Boral comes in 2" thick boards (which is ultimately only 1.5" thick) so it would protrude out from the framework of my window 3/16 (0.187")

    I wanted to use cedar... but I think i have something here...

  7. gtmsmith | | #13

    This is pretty frustrating...
    I thought you dont caulk the gap between the trim and drip cap
    Andersen has you plugging that gap with backer rod and caulk
    So where does the water go that is behind the siding or trim?

    1. Patrick_OSullivan | | #14

      Feel free to follow Andersen's instructions. Or feel free to do what seems to be more prudent. Of course, there's always the nagging warranty thing.

      Personally, I agree that that's a bad place for sealant (that's only going to fail at some point in the future anyway). But I'm not surprised Andersen suggests it. Their install guidelines still allow a "barrier method" (i.e. the bottom flange sealed) for the window install itself! I like my new Andersen windows, but I find the fact that they endorse an installation method that has huge potential to trap water to be absolutely baffling.

  8. gtmsmith | | #15

    So follow Andersens instructions...

    Then for my trim:

    If I use cedar to trim my windows, I then need a second drip cap on top of the top cedar board as well. Where the siding meets that top cedar board, I will have to flash things again, and NOT caulk that top portion...

    I am amazed I cannot find this scenario or even key words relating to this situation anywhere on the internet...

  9. Expert Member
    Peter Engle | | #16


    You don't caulk between the trim and the drip cap. You caulk between the window and the drip cap. That is not clear in the Andersen sketches, but that's the correct place for the caulk, so that water cannot run back under the drip cap. There should be a 1/8"-1/4" gap between the drip cap and the trim so that water can drain from behind the trim and so the trim doesn't sit in any water perched on the drip cap.
    Don't follow the "barrier method" instructions. Those are for wall designs that attempt to control all of the water at the outside face of the wall system, with no provision for water management behind the cladding. Those systems don't work.

    1. Patrick_OSullivan | | #17

      Hey Peter,

      Not sure if you meant to reply to me or gtmsmith. I was never suggesting to caulk between the trim and drip cap. I was commenting that I think Andersen's very clear suggestion to caulk between trim and *any part of the window* is silly and ill-advised. And I agree that their approval of the "barrier method" is asinine.

      I like my A series windows. But some of their installation instructions are at best questionable and at worst flat out wrong.

  10. gtmsmith | | #18

    Ok Marvin answered some of my questions/concerns... But there is still some anxiety over all of this haha...

    I now know that I am adding a drip edge to the top of my window and to the top edge of my cedar trim regardless how far one or the other is proud from the wall. The window will have a nice sloped and extended drip edge. The trim will just have an impervious edge folded over the trim a bit.

    I agree, Andersen's caulking/backer rod of all four sides doesnt make much sense today... or do they? If I have a drip edge on top of my trim above the window and a window drip edge, then does that trim drip edge get taped too? Right? So then water should never get behind the trim, thus never making it to the drip edge on the window... so why leave the window drip edge open to drain? Right?

    And if I am using a WRB that is draining, (Benjamin Obdyke Hydrogap WRB) completely closing the window in is 'ok', right?

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