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Community and Q&A

Wooden window trim joints

tannerc | Posted in General Questions on

Hey folks, I am planning to trim out the windows in my new construction with cedar mounted on rainscreen battens. Trim will be installed before and stand proud of the siding. Head trim will be given a metal drip cap. I’ve been grappling with and bugging the GBA community lately about siding joints and flashing details, but I believe this is just a bit different:

how should I join (or not join) my window trim? 

1. Like this FHB video where everything is pocket screwed tight together and then mounted in one go?

2. Or, given that I’ll be using wood instead of PVC, like this mock-up that I’ve just put together ( photo attached, side view, left side of the frame would be the top of the window). All portions that would be horizontal when on the wall have been sloped 15 degrees and all the pieces are given a roughly 1/16″ expansion gap. The pieces could all be mounted separately and not be fastened together. This method seems like it would be more consistent with my reading of Martin and Peter’s philosophy of keeping joints open and letting them drain and dry.

Thanks again, 

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  1. Expert Member
    Peter Yost | | #1

    Hi Tanner -

    Interesting. I did NOT gap my window trim; I gapped everything that came up to meet my window trim. I did seal the living daylights out of all my end grain before doing my window trim.

    18 years later, my only problems are where I have finger-jointed pre-primed trim. Those joints just do not hold up. But with all solid sawn, yours look great and will last.


  2. tannerc | | #2

    Great, thanks Peter! Just heard similar experiences from two carpenter friends. So you gapped the siding to trim joint, no caulk, correct?

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